Module: xenomai-forge Branch: next Commit: 65a9418f245c2138aa1bfb2d69975da3dbb6b0bd URL: http://git.xenomai.org/?p=xenomai-forge.git;a=commit;h=65a9418f245c2138aa1bfb2d69975da3dbb6b0bd
Author: Philippe Gerum <r...@xenomai.org> Date: Fri Jul 12 15:41:13 2013 +0200 slackspot: provide README with basic usage --- utils/slackspot/README | 84 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 84 insertions(+), 0 deletions(-) diff --git a/utils/slackspot/README b/utils/slackspot/README new file mode 100644 index 0000000..f1e94c8 --- /dev/null +++ b/utils/slackspot/README @@ -0,0 +1,84 @@ +== SLACKSPOT + +We desperately needed a way to help spotting code locations causing +spurious relaxes of real-time threads, at source level. + +Combining SIGXCPU receipts and the backtrace() utility directly from +the application code used to be the recommended way of doing this, but +this fell short of being really handy, simply because that debug +feature had to be implemented in an ad hoc manner within each new +application. + +With the advent of the copperplate library, with most RTOS APIs moving +to user-space on top of the POSIX skin, we really want a better, more +efficient approach to debug those issues over the Cobalt core, and we +want it available for any application in a snap, implemented once for +all. + +The approach chosen combines dedicated kernel support exporting trace +information about spurious relaxes through the debug/relax vfile, and +a userland utility called "slackspot", which parses the vfile output +to display the program backtrace, so that we can locate the offending +code easily. + +The motivation to centralize tracing information about relaxes +directly into kernel space is fourfold: + +- it allows to gather all the trace data into a single location and +keep it safe there, with no external log file involved. + +- enabling the tracing does not impose any requirement on the +application (aside of being compiled with debug symbols for best +interpreting that information). We only need a kernel config switch +for this (i.e. CONFIG_XENO_OPT_DEBUG_TRACE_RELAX). + +- the data is collected and can be made available exactly the same +way regardless of the application emitting the relax requests, or +whether it is still alive when the trace data are displayed. + +- the kernel is able to provide accurate and detailed trace +information, such as the relative offset of instructions causing relax +requests within dynamic shared objects, without having to guess it +roughly from /proc/pid/maps, or relying on ldd's --function-relocs +feature, which both require to run on the target system to get the +needed information. Instead, we allow a build host to use a +cross-compilation toolchain later to extract the source location, from +the raw data the kernel has provided on the target system. + +Here is a typical debugging session, involving a target board running +the Xenomai application, and a host system, providing the +cross-compilation toolchain used to build that application. We use the +netcat utility to pull the trace data over the wire from the target, +and process it locally on our debug host: + +target> netcat -l -p <port> -c < /proc/xenomai/debug/relax + +host> nc <target-ip> <port> | CROSS_COMPILE=ppc_6xx- ./slackspot --path=/opt/rootfs/MPC5200/lib:$HOME/frags/relax --filter thread=Task* + +Thread[828] "Task 2" started by /relax: + #0 0xfff00000 ??? + #1 0x000001bb ??? + #2 0x00064393 _IO_file_doallocate() in ??:? + #3 0x00073d6f _IO_doallocbuf() in ??:? + #4 0x00072d87 _IO_file_overflow() in ??:? + #5 0x00075f83 __overflow() in ??:? + #6 0x0006997b putchar() in ??:? + #7 0x100017db task2_func() in /home/rpm/frags/relax/relax.c:23 + #8 0x000078d7 rt_task_trampoline() in /home/rpm/git/xenomai-forge/src/native/task.c:115 + #9 0x00005a6b start_thread() in pthread_create.c:? + #10 0x000d389f __clone() in ??:? + +Thread[828] "Task 2" started by /relax (4 times): + #0 0x000c443f write() in ??:? + #1 0x00072553 _IO_file_write() in ??:? + #2 0x000721cf _IO_file_seek() in ??:? + #3 0x000724c7 _IO_do_write() in ??:? + #4 0x00072c2f _IO_file_sync() in ??:? + #5 0x00064a4f _IO_fflush() in ??:? + #6 0x100017eb task2_func() in /home/rpm/frags/relax/relax.c:24 + #7 0x000078d7 rt_task_trampoline() in /home/rpm/git/xenomai-forge/src/native/task.c:115 + #8 0x00005a6b start_thread() in pthread_create.c:? + #9 0x000d389f __clone() in ??:? + +Looks like someone is doing silly things both at lines 23 and 24 from +relax.c. Isn't this nice? _______________________________________________ Xenomai-git mailing list Xenomai-git@xenomai.org http://www.xenomai.org/mailman/listinfo/xenomai-git
