Debugging in Scratchbox
Contents
1. Chapter 2 Debugging One has to use sbrsh as the CPU transparency method because QEMU does not support gdb Currently gdbserver supports the following platforms arm linux gnu 1386 linux gnu e ia64 linux gnu m68k linux gnu mips linux gnu powerpc linux gnu sh linux gnu Chapter 3 Example session 3 1 general In this chapter we have an example session of gdb and gdbserver usage in Scratchbox Chapter is divided to multiple sections so that it is easier to see what is going on It is strongly advised to go trough this example to understand how gdb and gdbserver act together in Scratchbox This chapter assumes that one has correctly setup scratchbox installation with working CPU tranparency 6 3 2 setup First one needs a program to debug sbox ARM debug test gt cp scratchbox packages hello c sbox ARM debug test gt cat hello c include lt stdio h gt int main void printf hello world n return 0 sbox ARM debug test gt gcc g hello c sbox ARM debug test gt a out hello world sbox ARM debug test gt 3 3 gdbserver First copy gdbserver to target filesystem sbox ARM debug test gt sb conf install gdb sbox ARM debug test gt file usr bin gdbserver usr bin gdbserver ELF 32 bit LSB executable ARM version 1 ARM sbox ARM debug test gt for GNU Linux 2 0 0 d Then just launch it with correct c2. Debugging in Scratchbox Lauri Arimo Debugging in Scratchbox by Lauri Arimo Copyright 2004 2005 Nokia This is an document about debugging in Scratchbox environment Revision history Version Author Description 2005 02 15 Savola Removed gdbserver workaround 2005 02 08 ISavola Scratchbox 1 0 updates 2004 11 08 Arimo Added some details 2004 09 30 lArimo nitial revision Table of Contents 1 Introduction resserenserenverenvnvenenserenserensenensereneesensesensnsensnserenserenserensesenseseneesensnsensnserensenenserenseseneesensnsensnsene 1 1 1 Purpose of this document ccicsscccdeecivenncs e aE EE E E T A E A 1 12 Scratchbox environment anere i ec ie EE E E ri cite 1 pA MILIMESE T 2 2 1 Debugging tools provided by scratchbox ii 2 I2eStacCinia torcia eee 2 PA a lo PREPRE E EE EAEE eee ea 2 DA BODSCEVELS wii ia Deme E iaia 3 3 Example SESSION IRR 5 31 general z oeste deque eehi e i a eet BRAG Seine i E AR 5 32 SOUP ae 5 BDU PADSELVET sess at Bes ne REND RON EPIRI 5 EE EN NN NE 6 35agdb and corefiles 5 epatis ep Ei ee pREpAEURI sen 7 4 Graphical frontend T S 9 sae rh ese EE 9 4 2 SD DD i titi REAPER UR ei EHE RAO eres 9 jn r 10 iii Chapter 1 I
3. Gdbserver usage is described in more depth in the next chapter To use gdbserver you need to use the target remote ip port command in gdb To make debugging with gdb possible one should compile binaries with g flag so that debugging symbols are included in the binaries It is possible to use stripped binary with gdbserver and tell to gdb where to look for debug symbols with the symbol file path to file command This is explained in the Chapter 3 chapter Scratchbox s gdb has also been patched so that one should be able to read x86 and ARM core files on host machine This is a good way to find out what went wrong in the first place 2 4 gdbserver Gdbserver is a program that allows you to run gdb on a different machine than the one which is running the program being debugged This means that one can run binaries for different architecture on target device via Scratchbox s CPU trancparency feature Actual debugging can then be handled on host with the gdb provided by the toolchain To use gdbserver one has to first install it on the target It can be done using the following command sbox ARM gt sb conf install gdb Launching gdbserver is easy sbox ARM gt gdbserver lt ip gt lt port gt lt program gt lt arguments gt This will make gdbserver listen for TCP connections from host lt ip gt at port lt port gt It is also possible to attach gdbserver to an already running process with the attach lt pid gt option
4. U General Public License and you are elcome to change it and or distribute copies of it under certain conditions zOQ0Q0 o c c 3 1 ype show copying to see the conditions here is absolutely no warranty for GDB Type show warranty for details his GDB was configured as host i686 pc linux gnu target arm linux 3 1 3 1 warning core file may not match specified executable fil vr Core was generated by Program terminated with signal 11 Segmentation fault Reading symbols from lib libc so 6 done Loaded symbols for lib libc so 6 Reading symbols from lib ld linux so 2 done Loaded symbols 0 0x000083b0 13 gdb bt 0 0x000083b0 1 0x0000838c gdb for lib ld linux so 2 in a p 0x0 at segfault c 13 int y p in a p 0x0 at segfault c 13 in main at segfault c 7 Chapter 3 Example session Chapter 4 Graphical frontends 4 1 General It s possible to use some graphical frontend for scratchbox s gdb Perhaps the most popular of these is DDD The Data Display Debugger which can be used as frontend for many different debuggers The trick is to tell the frontend to use Scratchbox s gdb In this document DDD is used as an example Other frontends should work with same principles 4 2 DDD The Data Display Debugger DDD is a popular graphical user interface to UNIX debuggers such as GDB DBX XDB JDB and others Besides usual front end features
5. does not use CPU transparency for example when using an x86 target or when the CPU transparency method is QEMU Otherwise the script tries to execute the target binary usr bin strace If you want to use strace while using sbrsh for CPU transparency you can install strace on your target with the following command sbox ARM gt sb conf install strace Note Host strace can be used with QEMU because QEMU directs the target command s syscalls to the host kernel Strace can be used in two ways Either by running a new binary e g strace bin Is or by tracing existing process by specifying its process id e g strace p 4352 Other really useful flags are f to follow forks o to write output to file and e which can be used to filter output Detailed information can be found on strace s man page Chapter 2 Debugging 2 3 gdb GDB is a source level debugger capable of breaking programs at any specific line displaying variable values and determining where errors occurred gdb needs to be configured separately for each toolchain This is why it s built with the toolchains see Scratchbox toolchains 7 The user should not have to worry about this Scratchbox will put right version of gdb to the PATH One can find correct version of gdb from the scratchbox compilers lt compilername gt arch_tools bin directory If you plan to debug a binary for some other architecture than x86 you need to use gdbserver to run the binary
6. ing ran by gdbserver sbox ARM debug test gt gdb GNU gdb 6 1 Copyright 2004 Free Software Foundation Inc GDB is free software covered by the GNU General Public License and you are welcome to change it and or distribute copies of it under certain conditions ype show copying to see the conditions 3 here is absolutely no warranty for GDB Type show warranty for details This GDB was configured as host i686 pc linux gnu target arm linux gdb file a out Reading symbols from a out done gdb target remote 172 16 6 54 4444 Remote debugging using 172 16 6 54 4444 Chapter 3 Example session 0x40000d00 in gdb cont Continuing Program exited normally gdb One can set breakpoints etc before running program with cont After the program exits one has to restart gdbserver before new session 3 5 gdb and corefiles Scratchbox s gdb can handle corefiles for x86 and ARM targets Program must be compiled with debugging symbols ie g switch if some meaningful output is wanted sbox ARM debug test gt cat segfault c int a int p int main void int p 0 null pointer return a p int a int p int y p return y Sbox ARM debug test gt gcc g segfault c sbox ARM debug test gt a out sbox ARM debug test gt gdb a out core NU gdb 6 1 opyright 2004 Free Software Foundation Inc DB is free software covered by the GN
7. ntroduction 1 1 Purpose of this document This document introduces some tools that can be used for debugging and are provided with Scratchbox Focus is on describing differences between usage on native systems and Scratchbox This is not complete user manual for debugging tools although some good reference pointers are given Reader is assumed to have good Linux knowledge and some experience in debugging Good place to start gathering common knowledge about debugging in Linux environment is paper written by Movial 1 1 2 Scratchbox environment Scratchbox 2 is a cross compilation toolkit designed to make embedded Linux application development easier Due to the nature of Scratchbox there can be binaries for different architectures This mean that specially configured tools are needed for efficient debugging Chapter 2 Debugging 2 1 Debugging tools provided by scratchbox Scratchbox provides following debugging tools by default strace A system call tracer 3 gdb The GNU Debugger 4 gdbserver Remote Server for the GNU Debugger 5 2 2 strace Strace is a system call tracer i e a debugging tool which prints out a trace of all system calls made by another process program The program to be traced need not be recompiled for this so you can use it on binaries for which you don t have source In Scratchbox strace is used through a wrapper The wrapper uses a host version of strace when the compilation target
8. ommunication info and correct program with arguments sbox ARM debug test gt gdbserver 172 16 6 66 4444 a out Chapter 3 Example session Process a out created pid 642 Listening on port 4444 Gdbserver is now waiting connections from 172 16 6 66 to port 4444 It will wait until interrupted or successful connection is made After connection program execution goes as the gdb commands Below is one possible output sbox ARM debug test gt gdbserver 172 16 6 66 4444 a out Process a out created pid 642 Listening on port 4444 Remote debugging from host 172 16 6 66 hello world Child exited with retcode 0 Child exited with status 0 GDBserver exiting sbox ARM debug test gt Quite simple eh 3 4 gdb Check that correct gdb is in PATH sbox ARM debug test gt gdb v GNU gdb 6 1 Copyright 2004 Free Software Foundation Inc GDB is free software covered by the GNU General Public License and you are welcome to change it and or distribute copies of it under certain conditions ype show copying to see the conditions 3 here is absolutely no warranty for GDB Type show warranty for details 3 his GDB was configured as host i686 pc linux gnu target arm linux Sbox ARM debug test gt Launch gdb load correct symbols from a file and connect to the gdbserver Remember to use cont instead of run when starting the program This is because program is already be
9. such as viewing source texts and breakpoints DDD provides an interactive graphical data display where data structures are displayed as graphs Using DDD you can reason about your application by watching its data not just by viewing it execute lines of source code To launch DDD with Scratchbox s gdb use following command ddd debugger scratchbox login gdb More information about debugging with DDD can be found from 8 References 1 Debugging linux applications http www movial fi client data file movial_debugging_linux_applications pdf 2 Scratchbox website http scratchbox org 3 strace A system call tracer http www devchannel org article pl sid 03 10 24 2057246 4 gdb The GNU Debugger http sources redhat com gdb current onlinedocs gdb_toc html 5 gdbserver Remote Server for the GNU Debugger http sources redhat com gdb current onlinedocs gdb_18 html SEC 146 6 Scratchbox toolchains http scratchbox org documentation docbook installdoc html Ricardo Kekki 7 Installing Scratchbox http scratchbox org documentation docbook toolchain html Rahkonen Valtteri 8 DDD Data Display Debugger http www gnu org software ddd manual 10
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