User Manual - Frama-C
Contents
1. GTK 15 GtkSourceView 15 h 17 help 17 help 17 Installation 15 Interactive version 16 Journal 31 journal disable 31 journal enable 31 INDEX 47 Index journal name 31 keep comments 18 keep switch 24 kernel debug 17 kernel h 17 kernel help 17 kernel verbose 17 Lablgtk 15 lib entry 27 libdir 18 load 30 30 load module 22 35 load script 22 31 35 machdep 24 main 27 Native compiled 15 16 obfuscate 18 OCaml compiler 15 OcamlGraph 16 ocode 18 Options 16 overflow 27 Plug in Dynamic 21 22 35 External 21 22 Internal 21 21 Static 21 22 pp annot 23 Pragma UNROLL 24 print 18 24 print lib path 18 22 print plugin path 18 22 print share path 18 22 Project 29 quiet 17 INDEX safe arrays 28 30 save 30 30 simplify cfg 24 time 18 type check 25 ulevel 24 30 unsafe arrays 28 30 unspecified access 28 verbose 17 version 17 37 with all static 21 with no plugin 21 482. 2010 of Frama C However the development of Frama C is still ongoing features described here may still evolve in the future Acknowledgements We gratefully thank all the people who contributed to this document Patrick Baudin Micka l Delahaye Philippe Hermann and Benjamin Monate Inttp frama c cea fr Chapter 1 Introduction This is Frama C s user manual Frama C is an open source platform dedicated to the static analysis of source code written in the C programming language The Frama C platform gathers several static analysis techniques into a single collaborative framework This manual gives an overview of Frama C for newcomers and serves as a reference for ex perimented users It only describes those platform features that are common to all analyzers Thus it does not cover use of the analyzers provided in the Frama C distribution Value Anal ysis Slicing Each of these analyses has its own specific documentation 3 Furthermore the development of new analyzers is described in the Plug in Development Guide 4 1 1 About this document Appendix A references all the changes made to this document between successive Frama C releases In the index page numbers written like 1 reference the defining sections for the corresponding entries while other numbers like 1 are less important references Most important paragraphs are displayed inside a gray box like this one A plug in developer must foll
3. Specifications can be written in a dedicated language ACSL ANSI ISO C Specification Lan guage 2 The specifications can be partial concentrating on one aspect of the analyzed program at a time The most structured sections of your existing design documents can also be considered as formal specifications For instance the list of global variables that a function is supposed to read or write to is a formal specification Frama C can compute this information automatically from the source code of the function allowing you to verify that the code satisfies this part of the design document faster and with less risks than a code review 2 3 Frama C as a tool for C programs Frama C analyses C programs The C source code is assumed to follow the C99 ISO standard C comments may contain ACSL annotations 2 used as specifications to be interpreted by Frama C The subset of ACSL currently interpreted in Frama C is described in 1 Furthermore each analyzer may define the subsets of C and ACSL that it understands as well as introduce specific limitations and hypotheses Please refer to each plug in s documentation 2 4 Frama C as an Extensible Platform Frama C is extensible 12 2 5 FRAMA C AS A COLLABORATIVE PLATFORM It is is organized with a plug in architecture comparable to that of the Gimp or Eclipse each analyzer comes in the form of a plug n and is connected to the platform itself or kernel Several ready
4. The following options allow to customize the normalization annot forces Frama C to interpret ACSL annotations This option is set by default and is only found in its opposite form no annot which prevents interpretation of ACSL annotations constfold performs a syntactic folding of constant expressions For instance the expression 1 2 1s replaced by 3 continue annot error just emits a warning and discards the annotation when it fails to type check instead of generating an error errors in C are still fatal keep switch preserves switch statements in the source code Without this option they are transformed into if statements An experimental plug in may forgot the treatment of the switch construct and require this option not to be used Other plug ins may prefer this option to be used because it better preserves the structure of the original program machdep lt machine architecture name gt defines the target platform The default value is a x86 32bits platform Analyzers may take into account the endianness of the target the size and alignment of elementary data types and other architecture compilation parameters The machdep option provides a way to define all these parameters consis tently in a single step The list of supported platforms can be obtained by typing frama c machdep help simplify cfg allows Frama C to remove break continue and switch statements This op tion is automatically set by some plug ins tha
5. also a link to an advanced bugs reporting page that allows you to write a more detailed report The different fields of these forms shall be filled in English as precisely as possible in order for the maintenance team to understand and track the problem down easily Below are some recommendations for this purpose Category select as appropriate Reproducibility select as appropriate Severity select the level of severity Levels are shown in increasing order of severity Profile or Platform OS and OS Version enter your hardware and OS characteristics Product Version and Product Build this can be obtained through the command frama c version see Section 3 3 2 Summary give a brief one line description of the nature of your bug Description first explain the actual behavior that is what you actually observe on your system Then describe your expected behavior of Frama C that is the results you expect instead A bug is sometimes due to a misunderstanding of the tool s behaviour or a misunderstanding of its results so providing both behaviors is an essential part of the report Please do clearly separate both parts in the description Steps to reproduce provide everything necessary for a maintainer to reproduce the bug input files commands used sequence of actions etc If the bug appears through the Frama C GUI it may be useful to attach the generated journal see Section 7 3 Beware that this journal does not repl
6. are evaluated For instance This occurs with the following piece of code nt ia j gt FP 1 amp i i p nou 1 e i i p j In this code it is unclear in which order the elements of the right hand side of the last assignment are evaluated Indeed the variable j can get any value as i and p are aliased The unspecified access option aims at warn against such ambiguous situations 28 Chapter 7 zeneral Kernel Services This chapter presents some important services offered by the Frama C platform 7 1 Projects A Frama C project groups together one source code with the states parameters results etc of the Frama C kernel and analyzers In one Frama C session several projects may exist at the same time while there is always one and only one so called current project in which analyses are performed Thus projects help to structure a code analysis session into well defined entities For instance it is possible to perform one analysis on the same code with different parameters and to compare the obtained results It is also possible to extract a program p from an initial program p and to compare the results of an analysis run separately on p and p 7 1 1 Creating Projects A new project is created in the following cases e at initialization time a default project is created or e via an explicit user action in the GUI or e a source code transforming analysis has been made The analyzer then cre
7. generated Please refer to the specific documentation of each plug in in order to get the exact form of alarms the Console page displays messages to users in a textual way That is the very same output than the one shown in batch mode 8 2 Menu Bar The menu bar is organised as follows File Menu proposes items for managing the current session Item Set C source files allows to change the analyzed files of the current project Item Save session saves all the current projects into a file If the use never chooses such a file a dialog box is opened for choosing one Item Save session as saves all current projects into a file chosen from a dialog box Item Load Session opens a previously saved session This fully resets the current session see Section 7 1 3 Item Quit exits Frama C without saving Project Menu displays the existing projects allowing you to set the current one You can also perform miscellaneous operations over projects creating from scratch duplicating renaming removing saving etc Analyses Menu provides items for configuring and running plug ins e Item Configure and run analyses opens the dialog box shown Figure 8 2 that allows to set all Frama C parameters and to re run analyses according to changes 34 8 2 MENU BAR Customize parameters then click on Execute kernel b Finder gt Postdominators and postdominators gt from analysis gt impact gt inout b jes
8. ins it finds if the option dynlink is set That is the normal behavior you have to use its opposite form no dynlink in order to not load any dynamic plug in When loading dynamic plug ins Frama C searches for them in directories indicated by frama c print plugin path see Section 3 4 2 Frama C can locate plug ins in additional directories by using the option add path lt paths gt Yet another solution to load a dynamic plug in is to set the load module lt files gt or load script lt files gt options using in both cases a comma separated list of file names without any extension The former option loads the specified OCaml object files into the Frama C runtime while the latter tries to compile the source files before linking them to the Frama C runtime In general dynamic plug ins must be compiled with the very same OCaml compiler than Frama C was and against a consistent Frama C installation Loading will fail and a warning will be emitted at launch if this is not the case The load script option requires the OCaml compiler that was used to compile Frama C to be available and the Frama C compiled library to be found see Section 3 4 1 With the extension exe on Windows OS 22 Chapter 5 Preparing the Sources This chapter explains how to specify the source files that form the basis of an analysis project and describes options that influence parsing 5 1 Pre processing the Source Files The list of files to anal
9. the Bug Tracking System see Chapter 9 5 Frama C exits abnormally on an unknown error Please report a bug report on the Bug Tracking System see Chapter 9 19 Chapter 4 Working with Plug ins The Frama C platform has been designed to support third party plug ins In the present chapter we present how to configure compile install run and update such extensions This chapter does not deal with the development of new plug ins see the Plug in Development Guide 4 It does not deal with usage of plug ins which is the purpose of individual plug in manuals 4 1 The Plug in Taxonomy It is possible to distinguish 2 x 2 kinds of plug ins internal vs external plug ins and static vs dynamic plug ins These different kinds are explained below internal vs external Internal plug ins are those distributed within the Frama C kernel while external plug ins are those distributed independently of the Frama C kernel They only differ in the way they are installed see Sections 4 2 and 4 3 static vs dynamic Static plug ins are statically linked into a Frama C executable see Sec tion 3 2 while dynamic plug ins are loaded by an executable when it is run Despite only being available on some environments see Section 3 1 dynamic plug ins are more flexible as explained in Section 4 4 4 2 Installing Internal Plug ins Internal plug ins are automatically installed with the Frama C kernel If you use a source di
10. to use analyses are included in the Frama C distribution This manual covers the set of features common to all plug ins It does not cover use of the plug ins that come in the Frama C distribution Value Analysis Functional Dependencies etc Each of these analyses has its own specific documentation 3 Additional plug ins can be provided by third party developers and installed separately from the kernel 2 5 Frama C as a Collaborative Platform Frama C s analyzers collaborate with each other Each plug in may interact with other plug ins of his choosing The kernel centralizes information and conducts the analysis This makes for robustness in the development of Frama C while allowing a wide functionality spectrum For instance the Slicing plug in uses the results of the Value Analysis plug in and of the Functional Dependencies plug in Analyzers may also exchange information through ACSL annotations 2 A plug in that needs to make an assumption about the behavior of the program may express this assumption as an ACSL property Because ACSL is the lingua franca of all plug ins another plug in can later be used to establish the property With Frama C it will be possible to take advantage of the complementarity of existing analysis approaches It will be possible to apply the most sophisticated techniques only on those parts of the analyzed program that require them The low level constructs can for instance effectively be h
11. versions of Frama C obey a number of command line options Any option that exists in these two modes has the same meaning in both For instance the batch version can be made to launch the value analysis on the foo c file with the command frama c val foo c Although the GUI allows to select files and to launch the value analysis http ocamlgraph 1lri fr On Windows OS the usual extension exe is added to each file name For a single analysis project Multiple projects can only be handled in the interactive version or program matically see Section 7 1 16 3 3 FRAMA C COMMAND LINE AND GENERAL OPTIONS interactively the command frama c gui val foo c can be used to launch the value analysis on the file foo c and starts displaying the results immediately in the GUI Any option requiring an argument may use the following format option_name value If the option s argument is a string that is neither an integer nor a float etc the following format is also possible option_name value This last format must be used when value starts with a minus sign Most parameterless options have an opposite option often written by prefixing the option name with no For instance the option unicode for using the Unicode character set in messages has an opposite option no unicode for limiting the messages to ACSII Plug ins options with a name of the form lt plug in name gt lt option name gt have their opposite option named l
12. 1L 66 isize ulg ifile size NR erc outbuf tmp 17 unsigned char int unsigned short crc 65535UL gt 82 Trace stderr actual ld read ld ifile size isize 83 fprintf stderr s file size changed while zipping n ermo h 84 progname ifname stat h amp else 85 C undefined sequence prenda lS slici i E tmp 18 outcnt Y Slicing E gm qe 88 Write the crc and uncompressed size Activate on outbuf tmp 18 unsigned char crc 65535UL 255UL 89 put_long crc 90 put long isize UE if outcnt 16384U flush outbuf ne header by ten lt RE tiene er arie aye undefined sequence 92 E 2 A O tmp 19 outcnt 93 flush_outbuf Y Impact Plug ins View outent e Tetum oK Set sel outbuf tmp 19 unsigned char int unsigned short crc amp 65535UL dE E Enable Tr gt IG gt O Slicing after impact Information Messages Console O Follow focus Function zip Y Metrics Statement 163 line 73 in demos gzip 1 2 4 zip c Meas sloc la f if I Messages View goto a Ptr Fet P Cyclo Y Occurrence er 7 El Figure 8 1 Initial View From top to bottom the window is made of several separate sub parts namely The Menu Bar organizes the highest level functions of the tool into structured categories Plug ins may also add their
13. IX commands The OCaml compiler is required both for compiling Frama C from source and for compiling additional plug ins Version 3 10 2 or higher must be used Support of some plug ins in native compilation mode see Section 3 2 requires the so called native dynamic linking feature of OCaml It is only available in the most recent versions of OCaml at least 3 11 0 and only on a subset of supported platforms Gtk related packages GTK version 2 4 or higher GtkSourceView version 2 x Gnome Canvas version 2 x as well as LablGtk version 2 14 or higher are required for building the Graphical User Interface GUI of Frama C http www gnu org software make http caml inria fr http www gtk org nttp projects gnome org gtksourceview http library gnome org devel libgnomecanvas http wwwfun kurims kyoto u ac jp soft 1s1 lablgtk html 15 CHAPTER 3 GETTING STARTED OcamlGraph package Frama C will make use of OcamlGraph if already installed in version 1 4 or higher Otherwise Frama C will install a local and compatible version of this package by itself This dependency is thus non mandatory for Frama C 3 2 One Framework Four Executables Frama C installs four executables namely e frama c native compiled batch version e frama c byte bytecode batch version e frama c gui native compiled interactive version e frama c gui byte bytecode interactive version The differe
14. W possible targets of every pointer in the analyzed C program And lastly being available as a Frama C plug in increases your work s visibility among existing industrial users of Frama C The development of new plug ins is described in the Plug in Development Guide 4 14 Chapter 3 Getting Started This chapter describes how to install Frama C and what this installation provides 3 1 Installation The Frama C platform is distributed as source code Binaries are also available for popular architectures All distributions include the Frama C kernel and a base set of open source plug ins It is usually easier to install Frama C from one of the binary distributions than from the source distribution The pre compiled binaries include many of the required libraries and other dependencies whereas installing from source requires these dependencies already to have been installed The dependencies of the Frama C kernel are as follows Each plug in may define its own set of additional dependencies Instructions for installing Frama C from source may be found in the file INSTALL of the source distribution A C pre processor is required for using Frama C By default Frama C tries to use gcc C E I as pre processing command but this command can be customized see Sec tion 5 1 A Unix like compilation environment is mandatory and shall have at least the tool GNU make version 3 81 or higher as well as various POS
15. ace nor contain the input files that must be added to the bug report too see below French is also possible for private entries You can also have a look at the associated Frama C wiki http bts frama c com dokuwiki doku php id mantis frama c start 37 CHAPTER 9 REPORTING ERRORS Report Issue Frama C Bug Tracking System SeaMonkey File Edit View Go Bookmarks Tools Window Help GP Se IM http bts frama c com bug_report_page php a NINA Logged in as puccetti puccetti reporter 2009 09 15 16 18 CEST Details Advanced Report E public private check to report more issues Mantis 1 1 6 7 Copyright 2000 2008 Mantis Graup benjamin monategicea fr Figure 9 1 The BTS Bugs Reporting Page 38 Additional Information any extra information that might help the maintainer Industrial set it to true if you have a maintenance contract with the Frama C development team Upload File click on the Browse button to select a file for uploading Typically this is an archive that contains all files necessary for reproducing your problem It can include C source files shell scripts to run Frama C with your options and environment a Frama C journal etc Please check the size of the archive in order to to keep it manageable leave out any object code or executable files that can be easily rebuilt automatically by a shell script for instance View Status set it to private if your bu
16. allation instructions External plug ins are always dynamic plug ins by default On systems where native dynamic linking is not supported a new executable called frama c lt plug in name gt is automatically generated when an external plug in is compiled This executable contains the Frama C kernel all the static plug ins previously installed and the external plug in On systems where native dynamic linking is available this executable is not necessary for normal use but it may be generated with the command make static External dynamic plug ins may be configured and compiled with the Frama C kernel by using the option enable external lt path to plugin gt This option may be passed several times 4 4 Using Plug ins All Frama C plug ins define the following set of common options lt plug in shortname gt help or lt plug in shortname gt h prints out the list of options of the given plug in lt plug in shortname gt verbose lt n gt sets the level of verbosity to some positive integer n A value of 0 means no information messages Default is 1 lt plug in shortname gt debug lt n gt sets the debug level to a positive integer n The higher this number the more debug messages are printed Debug messages do not have to be understandable by the end user This option s default is O no debugging message Please refer to each plug in s documentation for specific options At launch Frama C loads all dynamic plug
17. arious metrics examples are the number of comments per line of code and the depth of nested control structures This kind of syntactic analysis can be implemented in Frama C but it is not the focus of the project Others may be familiar with heuristic bug finding tools These tools take more of an in depth look at the source code and try to pinpoint dangerous constructions and likely bugs locations in the code where an error might happen at run time These heuristic tools do not find all such bugs and sometimes they alert the user for constructions which are in fact not bugs Frama C is closer to these heuristic tools than it is to software metrics tools but it has two important differences with them it aims at being correct that is never to remain silent for a location in the source code where an error can happen at run time And it allows its user to manipulate functional specifications and to prove that the source code satisfies these specifications Frama C is not the only correct static analyzer out there but analyzers of the correct family are less widely known and used Software metrics tools do not guarantee anything about the behavior of the program only about the way it is written Heuristic bug finding tools can be very useful but because they do not find all bugs they can not be used to prove the absence of bugs in a program Frama C on the other hand can guarantee that there are no bugs in a program no bugs meaning either
18. ates a new project based on the original project and containing the modified source code typical example is code slicing which tries to simplify a program by preserving a specified behaviour 7 1 2 Using Projects The list of existing projects of a given session is visible in the graphical mode through the Project menu see Section 8 2 Among other actions on projects duplicating renaming removing savingetc this menu allows the user to switch between different projects during the same session In the batch mode it is not possible to handle a multi project session there is no way to switch from one project to another one through the command line 29 CHAPTER 7 GENERAL KERNEL SERVICES 7 1 3 Saving and Loading Projects A session can be saved to disk and reloaded by using the options save lt file gt and load lt file gt respectively Saving is performed when Frama C exits without error T he same oper ations are available through the GUI When saving all existing projects are dumped into an unique non human readable file When loading the following actions are done in sequence 1 all the existing projects of the current session are deleted 2 all the projects stored in the file are loaded 3 the saved current project is restored 4 Frama C is replayed with the parameters of the saved current project except for those parameters explicitely set in the current session Consider for instance the follo
19. er 3 4 2 Variable FRAMAC PLUGIN 0 0 0 00 00 004 debo Variable FRAMAD SHARE vou cocos ee aaa ee ee ee ee ea a CONTENTS Working with Plug ins 4 1 The Plug in Taxonomy 2 se u 2 4 144 eh de week a 4 2 Installing Internal Plug ins 2 22 04 4 3 Installing External Plug ins 2 20 a 44 Using Plug ins 1 ee 5 Preparing the Sources 5 1 Pre processing the Source Files CE nme een 5 2 Merging the Source Code files 5 3 Normalizing the Source Code 5 4 Testing the Source Code Preparation e 6 Analysis Options FL OM O deso eR eee AAA 02 toma AMO IE 7 General Kernel Services do EMO sppde gre rADR ee SED pd dd Creating Projects 2 se ewe eh ee Re ra Ile Woe POCO zo 8 4 ee eee ee ios der 7 1 3 Saving and Loading Projects 7 2 Dependencies between Analyses nr fo JOAO a e Bt Re eh wee RE dr 8 Graphical User Interface 8 1 Frama C Main Window 8 2 Menu Bar ee a a Sd 9 Reporting Errors A Changes Bibliography List of Figures Index 21 21 21 22 22 23 23 24 24 25 27 27 27 29 29 29 29 30 30 31 33 33 34 37 41 43 45 47 Foreword This is the user manual of Frama C The content of this document corresponds to the version Boron 20100401 April 13
20. fa a Frama C ES File Project Analyses Help Menu Bar 4 Ba E35 E33 A Toolbar le icin 2 mp 14 OUTCNT E q pews file Occuneoce Impact Silein ll pa E jdemos gzip 1 2 4 zip c ip h outbuf tmp 14 unsigned char p pa A pe ca u e a di 64 put byte uch deflate flags extra flags Le ERE if outcnt 163844 flush outbuf 65 put byte OS CODE 05 identifier b Izw c tmp 15 p E ai aro p 67 if save orig name ls E E if tmp 15 break 68 char p basename ifname Don t save the directory part D trees c A i 69 do b unizh c l Normalized Source Code View y ritos Original Source Code View gt unlzw c File Tree header_bytes Long outcnt 72 ki I 0 deflate b unpack c if outcnt lt unsigned int 16384 2 73 header bytes long outcnt gt unzip c undefined sequence 74 i tmp 16 outcnt 75 void deflate D util c p_ ps outent v ZIp c outbuf tmp 16 unsigned char crc 65535UL 255UL 77 if defined NO SIZE CHECK amp amp defined RECORD I0 file read 78 Check input size but not in VMS variable record lengths mess it up Ze undefined sequence 79 and not on MSDOS diet in TSR mode reports an incorrect file size s tmp_17 outcnt 80 ss at er zip outent 81 if ifile size
21. frama Software Analyzers User Manual 2 4 4 1 0 a ne 1 o 0 kes 2 jul np MEN duc fi Sa list Frama C User Manual Release Boron 20100401 Loic Correnson Pascal Cuoq Armand Puccetti and Julien Signoles CEA LIST Software Reliability Laboratory Saclay F 91191 2009 CEA LIST CONTENTS Contents Foreword 7 1 Introduction 9 1 1 About this document oe we kG RR RA ee a RESETE lila OUI score he na ihn tete sahen ehe 9 2 Overview 11 2 1 What is FAMA circa arar rra 11 2 2 Frama C as a Static Analysis Tool o 2 2 CC Eon onen 11 2 2 1 Frama C as a Lightweight Semantic Extractor Tool 12 2 2 2 Frama C for Formal Verification of Critical Software 12 2 3 Frama C as a tool for C programs 2 2 HH En 12 2 4 Frama C as an Extensible Platform 12 2 5 Frama C as a Collaborative Platform EEE nn a 13 2 6 Frama C as a Development Platform 2 2222 2 a Emm a 13 3 Getting Started 15 Oe MENUO ee ee HRS RE PER 15 3 2 One Framework Four Executables 2 2222 CE En m nn 16 3 3 Frama C Command Line and General Options 16 Bok ed Help once nenn nn a a ora 17 3 32 Fama Versi n una oH Aw eee RO RE en 17 poe Verbosity and Debugging Levels o sas sia won u Sa 17 Dae RUC UE ciar aka iur 18 3 3 5 Inputs and Outputs of source code 3 4 Environment Variables 2 2 2 Co aoao a a a a 34 1 Variable PRAMAC LTE o sss dae ek ha wee a
22. g should not be visible by others users Only yourself and the Frama C developers will be able to see your bug report Report Stay tick if this report shall remain open for further additions After submitting the report you will be notified by e mail about its progress and enter inter active mode on the BTS if necessary 39 Appendix A Changes This chapter summarizes the changes in this documentation between each Frama C release First we list changes of the last release e Preparing the Sources document usage of the C standard library delivered with Frama C e Graphical User Interface simplified and updated according to the new implemen tation e Getting Started document environment variables altogether e Getting Started document all the ways to getting help e Getting Started OcamlGraph 1 4 instead 1 3 will be used if previously installed e Getting Started GtkSourceView 2 x instead of 1 x is now required for building the GUI e Getting Started documentation of the option float digits e Preparing the Sources documentation of the option continue annot error e Using plug ins new option dynlink e Journalisation a journal is generated only whenever Frama C crashes on the GUI e Configure new option with no plugin e Configure option with all static set by default when native dynamic loading is not available Beryllium 20090902 e First public release 41 BIBLIOGRAPHY Bibliograp
23. hy 1 Patrick Baudin Pascal Cuoq Jean Christophe Filli tre Claude March Benjamin Monate Yannick Moy and Virgile Prevosto ACSL ANSI ISO C Specification Language Version 1 4 Frama C Beryllium implementation October 2009 2 Patrick Baudin Jean Christophe Filli tre Claude March Benjamin Monate Yannick Moy and Virgile Prevosto ACSL ANSI ISO C Specification Language preliminary de sign V1 4 preliminary edition October 2008 Lo 13 Pascal Cuoq and Virgile Prevosto Frama C s value analysis plug in October 2009 http frama c cea fr download value analysis Beryllium 20090902 pdf 4 o Julien Signoles Loic Correnson and Virgile Prevosto Frama C Plug in Development Guide September 2009 http frama c cea fr download plugin developer Beryllium 20090902 pdf 43 LIST OF FIGURES List of Figures A SIE 33 8 2 The Analysis Configuration Window a e 39 9 1 The BTS Bugs Reporting Page nn 38 45 absolute valid range 27 ACSL 12 13 23 24 add path 22 annot 24 Batch version 16 Bytecode 16 C pre processor 15 C99 ISO standard 12 constfold 24 continue annot error 24 cpp command 23 cpp extra args 23 datarootdir 18 debug 17 dynlink 22 enable external 22 float digits lt n gt 18 frama c 16 frama c gui 16 33 frama c gui byte 16 33 frama c byte 16 FRAMAC_LIB 18 FRAMAC_PLUGIN 18 FRAMAC_SHARE 18
24. idden from them by high level specifications verified by other adapted plug ins Note that the sound collaboration of plug ins on different parts of a same program that require different modelizations of C is work in progress At this time a safe restriction for using plug in collaboration is to limit the analyzed program and annotations to those C and ACSL constructs that are understood by all involved plug ins 2 6 Frama C as a Development Platform Frama C may be used for developing new analyses The collaborative and extensible approach of Frama C allows powerful plug ins to be written with relatively little effort There are a number of reasons for a user of Frama C also to be interested in writing his her own plug in e acustom plug in can emit very specific queries for the existing plug ins and in this way obtain information which is not easily available through the normal user interface e acustom plug in has more latitude for finely tuning the behavior of the existing analyses e some analyses may offer specific opportunities for extension If you are a researcher in the field of static analysis using Frama C as a testbed for your ideas is a choice to consider You may benefit from the ready made parser for C programs with ACSL annotations The results of existing analyses may simplify the problems that are orthogonal to those you want to consider in particular the Value Analysis provides sets of 13 CHAPTER 2 OVERVIE
25. ll analyzers should treat the function function_name as the entry point of the program lib entry indicates that analyzers should not assume globals to have their initial values at the beginning of the analysis This option together with the specification of an entry point f can be used to analyze the function f outside of a calling context even if it is not the actual entry point of the analyzed code 6 2 Customizing Analyzers The descriptions of the analysis options follow For the first two the description comes from the Value Analysis manual 3 Furthermore these options are very likely to be modified in future versions of Frama C absolute valid range m M specifies that the only valid absolute addresses for reading or writing are those comprised between m and M inclusive This option currently allows to specify only a single interval although it could be improved to allow several intervals in a future version no overflow instructs the analyzer to assume that integers are not bounded and that the analyzed program s arithmetic is exactly that of mathematical integers This option should only be used for codes that do not depend on specific sizes for integer types and do not rely on overflows For instance the following program is analyzed as non terminating in this mode void main void int x 1 while x return 2T CHAPTER 6 ANALYSIS OPTIONS The option no overflow should only be ac
26. lysis since the parameters have not been changed Consider now the two following commands frama c save foo sav ulevel 5 unsafe arrays val foo c frama c load foo sav safe arrays 30 7 3 JOURNALISATION The first commands produces the very same result than above However when loading Frama C knows that one parameter changed Thus it discards the saved results of the value analysis and recomputed it on the same source code by using the parameter ulevel 5 safe arrays and the default value of each other parameter In the same way results of one analysis A may depend on results of another one Aa So whenever results of Aa change Frama C automatically discards results of A For instance slicing results depend on value analysis results Thus the slicing results are discarded whenever the value analysis ones are 7 3 Journalisation Journalisation logs each operation that modifies some parameters or results into a file called a journal Observational operations like viewing the set of possibles values of a variable in the GUI are not logged By default the name of the journal is frama_c_journal ml but it can be modified by using the option journal name A journal is a valid Frama C dynamic plug in Thus it can be loaded by using the option load script see Section 4 4 The journal replays the very same results than the ones computed in the original session Journals are usually used for the three differen
27. nces between these versions are described below native compiled vs bytecode native executables contain machine code while bytecode executables contain machine independent instructions which are run by a bytecode in terpreter The native compiled version is usually ten times faster than the bytecode one The bytecode version supports dynamic loading on all architectures and is able to provide better debugging information Use the native compiled version unless you have a reason to use the bytecode one batch vs interactive The interactive version allows to use a GUI to select the set of files to analyze position options launch analyses browse the code and observe analysis results at one s convenience see Chapter 8 for details With the batch version all settings and actions must be provided on the command line This is not possible for all plug ins nor is it always easy for beginners Modulo the limited user interactions the batch version allows the same analyses as the interactive version A batch analysis session consists in launching Frama C in a terminal Results are printed on the standard output The task of analysing some C code being iterative and error prone Frama C provides functionalities to set up an analysis project observe preliminary results and progress until a complete and satisfactory analysis of the desired code is obtained 3 3 Frama C Command Line and General Options The batch and interactive
28. no possibility of a run time error or even no deviation from the functional specification the program is supposed to adhere to This of course requires more work from the user than heuristic bug finding tools usually do but some 11 CHAPTER 2 OVERVIEW of the analyses provided by Frama C require comparatively little intervention from the user and the collaborative approach proposed in Frama C allows the user to get some impressive results 2 2 1 Frama C as a Lightweight Semantic Extractor Tool Frama C analyzers may be useful for better understanding a C program by extracting semantic information from its code The C language has been in use for a long time and numerous programs today make use of C routines This ubiquity is due to historical reasons and to the fact that C is well adapted for a significant number of applications e g embedded code However the C language exposes many notoriously awkward constructs Many Frama C plug ins are able to reveal what the analyzed C code actually does Equipped with Frama C you can for instance e observe sets of possible values for the variables of the program at each point of the execution e slice the original program into simplified ones e navigate the dataflow of the program from definition to use or from use to definition 2 2 2 Frama C for Formal Verification of Critical Software Frama C allows to verify that source code complies with provided formal specifications
29. ow them very carefully 1 2 Outline The remainder of this manual is organized in several chapters Chapter 2 provides a general overview of the platform Chapter 3 describes the basic elements for starting the tool in terms of installation and commands Chapter 4 explains how to work with plug ins Chapter 5 presents the options of the source code pre processor Chapter 6 gives some general options for parametrising analyzers Chapter 7 introduces general services offered by the platform CHAPTER 1 INTRODUCTION Chapter 8 gives a detailed description of the graphical user interface of Frama C Chapter 9 explains how to report errors via the Frama C s Bug Tracking System 10 Chapter 2 Overview 2 1 What 1s Frama C Frama C is a platform dedicated to the static analysis of source code written in C The Frama C platform gathers several static analysis techniques into a single collaborative extensible framework The collaborative approach of Frama C allows static analyzers to build upon the results already computed by other analyzers in the framework Thanks to this approach Frama C provides very sophisticated tools such as a slicer and dependency analysis 2 2 Frama C as a Static Analysis Tool Static analysis of source code is the science of computing synthetic information about the source code without executing it To most programmers static analysis means measuring the source code with respect to v
30. own entries in the Analyses menu 33 CHAPTER 8 GRAPHICAL USER INTERFACE The Toolbar gives access to the main functions of the tool Their are usually present in one menu of the menu bar Plug ins may also add their own entries here The File Tree provides a tree like structure of the source files involved in the current analy sis as well as the functions they contain Plug ins may also display specific information for each file and or function The normalized and original source code views display the source code of the current selected element of the file tree and its normalised code see Section 5 3 Left clicking on an object statement left value etc in the normalized source code view displays information about it in the Information page of the Messages View and displays the corresponding object of the original source view while right clicking on them open a contextual menu Items of this menu depends of the kind of the selected object and of available plug ins Only the normalized source view is interactive the original one is not The Plug ins View shows specific interface of plug ins The interface of each plug in can be hidden The Messages View contains three different pages namely the Information page which provides brief details on the currently selected object the Messages page shows most important messages especially all the alarms that the Frama C kernel or plug ins
31. r verbose O debug 0 In the same way that verbose resp debug sets the level of verbosity resp debugging the options kernel verbose resp kernel debug and lt plug in name gt verbose resp lt plug in name gt debug set the level of verbosity resp debugging of the kernel and par ticular plug ins While both the global level of verbosity resp debugging and a specific one are modified the specific one applies For instance verbose O slicing verbose 1 runs Frama C quietly except for the slicing plug in 17 CHAPTER 3 GETTING STARTED 3 3 4 Getting time The option time lt file gt appends user time and date to the given log lt file gt at exit 3 3 5 Inputs and Outputs of source code The following options deal with inputs and outputs of analyzed source code print causes Frama C s representation for the analyzed source files to be printed as a single C program see Section 5 3 ocode lt file name gt redirects all output code to the designated file float digits lt n gt displays n digits when printing floats Defaults to 12 keep comments keeps C comments in lined in the code obfuscate can only be used alone to obfuscate C code Once done Frama C exits 3 4 Environment Variables Different environment variables may be set to customize Frama C 3 4 1 Variable FRAMAC_LIB External plug ins see Section 4 3 or scripts see Section 4 4 are compiled against the Frama C compiled lib
32. rary The Frama C option print lib path prints the path to this library The default path to this library may be set when configuring Frama C by using the configure option libdir After Frama C installation you can also set the environment variable FRAMAC_LIB to change this path 3 4 2 Variable FRAMAC_PLUGIN Dynamic plug ins see Section 4 4 are searched in a default directory The Frama C option print plugin path prints the path to this directory It can be changed by setting the environment variable FRAMAC_PLUGIN 3 4 3 Variable FRAMAC_SHARE Frama C looks for all its other data installed manuals configuration files C modelization libraries etc in a single directory The Frama C option print share path prints this path The default path to this library may be set when configuring Frama C by using the configure option datarootdir After Frama C installation you can also set the environment variable FRAMAC_SHARE to change this path 18 3 5 EXIT STATUS 3 5 Exit Status When exiting Frama C has one of the following status O Frama C exits normally without any error 1 Frama C exits because an user input was invalid 2 Frama C exits because the user kills it usually via Ctrl C 3 Frama C exits because the user tries to use an unimplemented feature Please report a feature request on the Bug Tracking System see Chapter 9 4 Frama C exits on an internal error Please report a bug report on
33. ry is bundled with Frama C and in stalled in the sub directory libc of the directory D printed by frama c print share path It contains standard C headers some ACSL specifications and definitions for some library functions You may use the following command frama c cpp extra args ID libc nostdinc D libc fc_runtime c lt input file gt Note that this standard library is customized for 32 bits little endian architecture For other configurations you have to manually edit the file D 1ibc __fc_machdep h 23 CHAPTER 5 PREPARING THE SOURCES 5 2 Merging the Source Code files After pre processing Frama C parses type checks and links the source code It also performs these operations for the ACSL annotations optionally present in the program Together these steps form the merging phase of the creation of an analysis project Frama C aborts whenever any error occurs during one of these steps However users can use the option continue annot error in order to continue after emiting a warning when an ACSL annotation fails to type check 5 3 Normalizing the Source Code After merging the project files Frama C performs a number of local code transformations in the normalization phase These transformations aim at making further work easier for the analyzers Analyses take place exclusively on the normalized version of the source code The normalized version may be printed by using the option print see Section 3 3 5
34. sie gt Itl to acsl gt metrics b occurrence pdg scope gt security gt semantic callgraph gt semantic constant folding gt slicing gt sparecode b syntactic callgraph b users gt value analysis b wp Figure 8 2 The Analysis Configuration Window e Item Compile and run an ocaml script allows you to run an OCaml file as a dynamic plug in in a similar way to the option load script see Section 4 4 e Item Load and run an ocaml module allows you to run a pre compiled OCaml file as a dynamic plug in in a similar way to the option load module see Section 4 4 e Other items are plug in specific The toolbar also provides a button Stop which halts the running analyses and restores Frama C in the last enable valid configuration Debug Menu is only visible in debugging mode and provides access to tools for helping to debug Frama C and their plug ins Help Menu provides help items 35 Chapter 9 Reporting Errors If Frama C crashes or behaves abnormally you are invited to bug report via the Frama C Bugs Tracking System BTS located at http bts frama c com Opening a BTS account is required for such a task Bug reports can be marked as public or private Public bug reports can be read by anyone and are indexed by search engines Private bug reports are only shown to Frama C developers Reporting a new issue open a webpage similar to the one shown Figure 9 1 This page has
35. stribution of Frama C it is possible to disable resp force the in stallation of a plug in of name lt plug in name gt by passing the configure script the option disable lt plug in name gt resp enable lt plug in name Disabling a plug in means it is neither compiled nor installed Forcing the compilation and installation of a plug in against configure s autodetection based default may cause the entire Frama C configuration to fail You can also use the option with no plugin in order to disable all plug ins Internal dynamic plug ins may be linked statically This is achieved by passing configure the option with lt plug in name gt static It is also possible to force all dynamic plug ins to be linked statically with the option with all static This option is set by default on systems unsupporting native dynamic loading 21 CHAPTER 4 WORKING WITH PLUG INS 4 3 Installing External Plug ins For installing an external plug in Frama C must be properly installed first In particu lar frama c print share path and must return the share directory of Frama C see Sec tion 3 4 3 while frama c print lib path must return the directory where the Frama C compiled library is installed see Section 3 4 1 The standard way for installing an external plug in from source is to run the sequence of commands make amp amp make install possibly preceded by configure Please refer to each plug in s documentation for inst
36. t cannot handle these kinds of statements This option is set by default ulevel lt n gt unrolls all loops n times This is a purely syntactic operation Loops can be unrolled individually by inserting the UNROLL pragma just before the loop state ment Do not confuse this option with plug in specific options that may also be called unrolling 3 Below is a typical example of use loop pragma UNROLL LOOP 10 for i 0 i lt 9 i 24 5 4 TESTING THE SOURCE CODE PREPARATION 5 4 Testing the Source Code Preparation If the steps up to normalization succeed the project is then ready for analysis by any Frama C plug in It is possible to test that the source code preparation itself succeeds by running Frama C without any option frama c lt input files gt If you need to use some options for pre processing or normalizing the source code you can use the option type check for the same purpose For instance frama c cpp command gcc C E I x c type check filel src file2 i 25 Chapter 6 Analysis Options The analysis options described in this chapter provide hypotheses that influence directly the behavior of analyzers For this reason the user must understand them and the interpretation the plug ins he uses have of them 6 1 Entry Point The following options define the entry point of the program and related initial conditions main lt function_name gt specifies that a
37. t plug in name gt no lt option name gt For instance the opposite of option ltl acceptance is 1t1 no acceptance 3 3 1 Getting Help The options of the Frama C kernel i e those which are not specific to any plug in can be printed out through either the option kernel help or kernel h The options of a plug in are displayed by using either the option lt plug in name gt help or lt plug in name gt h Furthermore either the option help or h or help lists all available plug ins 3 3 2 Frama C Version The current version of the Frama C kernel can be obtained with the option version This option also prints the different paths where Frama C searches objects when required 3 3 3 Verbosity and Debugging Levels The Frama C kernel and plug ins usually output messages either in the GUI or in the console Their levels of verbosity may be set by using the option verbose lt level gt By default this level is 1 Setting 1t to O limits the output to warnings and error messages while setting 1t to a number greater than 1 displays additional informative message progress of the analyses etc In the same fashion debugging messages may be printed by using the option debug lt level gt By default this level is 0 no debugging message is printed By contrast with standard messages debugging messages may refer to the internals of the analyzer and may not be understandable by non developers The option quiet is a shortcut fo
38. t purposes described thereafter e Replay easily a given set of analysis operations in order to reach a certain state Once the final state is reached further analyses can be performed normally Beware that journals may be source dependent and thus can not necessarily be reused on different source codes to perform the same analyses e Act as a macro language for plug in developers They can perform some wished actions on the GUI to generate a journal and then adapt it to perform a more general but similar task e Debugging In the GUI a journal is always generated even when an error occurs The output journal usually contains information about this error T hus it provides an easy way to reproduce the very same error Consequently it is advised to attach the journal when reporting an error in the Frama C BTS see Chapter 9 By default a journal is generated upon exit of the session only whenever Frama C crashes in graphical mode In all other cases no journal is generated This behaviour may be customized by using the option journal enable resp journal disable that generates resp does not generate a journal upon exit of the session 31 Chapter 8 Graphical User Interface Running frama c gui or frama c gui byte displays the Frama C Graphical User Interface GUD 8 1 Frama C Main Window Upon launching Frama C in graphical mode on some C files the following main window is displayed figure 8 1
39. tivated when it is guaranteed that the sizes of integer types do not change the concrete semantics of the analyzed code Beware voluntary overflows that are a deliberate part of the implemented algorithm are easy enough to recognize and to trust during a code review Unwanted overflows on the other hand are rather difficult to spot using a code review The next example illustrates this difficulty Consider the function abs that computes the absolute value of its int argument int abs int x 4 lt 20 er e return x 3 With the no overflow option the result of this function is a positive integer for what ever integer passed to it as an argument This property is not true for a conventional ar chitecture where abs MININT overflows and returns MININT Without the no overflow option on the other hand the value analysis detects that the value returned by this function abs may not be a positive integer if MININT is among the arguments The option no overflow may be modified or suppressed in a later version of the plug in unsafe arrays is useful when the source code manipulates arrays within structures It assumes that accesses in the array are always within the correct bounds No warnings are then emitted about possible out of bounds The opposite option called safe arrays is set by default unspecified access may be used to check when the evaluation of an expression depends on the order in which its sub expressions
40. wing command frama c load foo sav val It loads all projects saved in the file foo sav Then it runs the value analysis in the new current project if and only if it was not already computed at save time Recommendation 7 1 Saving the result of a time consuming analysis before trying to use it in different settings may be a good idea Beware that all the existing projects are deleted even if an error occurs when reading the file T hus in the GUI do not hesitate to save the existing projects in some file before loading another file 7 2 Dependencies between Analyses Usually analyses do have parameters see Chapter 6 Whenever values of parameters changes results of the analyses may change In order to not display inconsistent results according to the current value of parameters Frama C automatically discards results of an analysis when one of the analysis parameters changes Consider the two following commands frama c save foo sav ulevel 5 unsafe arrays val foo c frama c load foo sav Frama C runs the value analysis plug in on the file foo c where loops are unrolled 5 times option ulevel see Section 5 3 For computing its result the value analysis assumes that accesses in the array are always within the correct bound option unsafe arrays see Sec tion 6 2 Just after Frama C saves the results on file foo sav and exists At loading time Frama C knows that it is not necessary to redo the value ana
41. yse must be provided on the command line An alternative is to choose the files interactively in the GUI Files with the i suffix are assumed to be already pre processed C files Frama C pre processes the other files with the following command gcc C E I The option cpp command may be used to change the default pre processing command If patterns 41 and 2 do not appear in the provided command the pre processor is invoked in the following way lt cmd gt o lt output file gt lt input file gt In this command lt output file gt is chosen by Frama C while lt input file gt is one of the filenames provided by the user It is also possible to use the patterns 1 and 2 in the command as place holders for the input files and the output file respectively Here are some examples for using this option frama c cpp command gcc C E I x c filet sre file2 i frama c cpp command gcc C E I o 2 1 filel c file2 i frama c cpp command cp 1 42 filel c file2 i frama c cpp command cat 1 gt 2 filel c file2 i frama c cpp command CL exe C E 1 gt 2 filel c file2 i Additionally the option cpp extra args allows the user to extend the pre processing com mand By default ACSL annotations are not pre processed Pre processing them requires to use gcc as pre processor and to put the option pp annot on the Frama C command line An experimental incomplete specific C standard libra
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