WWW-www.enlightenment.org pushed a commit to branch master. http://git.enlightenment.org/website/www-content.git/commit/?id=6ea39bb7b9ac7d23012f6ec85a6c0ea6df3f5c04
commit 6ea39bb7b9ac7d23012f6ec85a6c0ea6df3f5c04 Author: Andrew Williams <[email protected]> Date: Fri Oct 20 08:36:06 2017 -0700 Wiki page enlightenment_debugging changed with summary [refactoring contrib pages] by Andrew Williams --- pages/contrib/enlightenment_debugging.txt | 238 ++++++++++++++++++++++++++++++ 1 file changed, 238 insertions(+) diff --git a/pages/contrib/enlightenment_debugging.txt b/pages/contrib/enlightenment_debugging.txt new file mode 100644 index 00000000..f68da329 --- /dev/null +++ b/pages/contrib/enlightenment_debugging.txt @@ -0,0 +1,238 @@ +~~Title: Enlightenment debugging~~ +==== Enlightenment Debugging ==== + +<note important> +//Please also see [[docs-efl-debug]]. This should probably be merged with this page.// +</note> + +This tutorial aims at providing a comprehensive and reproducible documentation to debug Enlightenment. It is divided in two sections: + + * [[#Debugging_Enlightenment_using_GDB|GDB]] + * [[#Valgrind|Valgrind]] + +Before debugging make sure your debug symbols are enabled, if not, go to the [[/docs-efl-start#Enable_debug_symbols_Optional|Enable debug symbols]] section. + +=== Debugging Enlightenment using GDB === + +In order to use GDB, we will simulate a crash in Enlightenment. + +Start by running Enlightenment on a machine. Then switch to another tty (CTRL+ALT+F1 for tty1). + +At that point, 2 processes are interesting, ''enlightenment'' and ''enlightenment_start''. Indeed, ''enlightenment'' is traced by ''enlightenment_start''. + +Then setup SEGV to segfault enlightenment. + +<code c> +kill -SIGSEGV $(pidof enlightenment) +</code> + +''enlightenment_start'' will open a pop-up named Enlightenment Error. This pop-up indicates that Enlightenment segfaulted and allows to recover or log out but also detaches from the child process (Enlightenment) and let advanced users use GDB to debug it. + +<code bash> +#gdb on the running enlightenment process +gdb enlightenment $(pidof enlightenment) +</code> + +After a bit a prompt is available, if you want, you can save the traces in a log: + +<code bash> +#save the traces in log.txt +set logging file log.txt +set logging on +</code> + +== Backtrace == + +Use the backtrace command to get information about frames to know where the segfault is coming from. + +<code bash> +(gdb) bt +#0 0xb7d539f8 in select () from /lib/tls/libc.so.6 +#1 0xb7dff66a in _XEnq () from /usr/X11R6/lib/libX11.so.6 +#2 0xb7dffa7e in _XRead () from /usr/X11R6/lib/libX11.so.6 +#3 0xb7e01795 in _XReadEvents () from /usr/X11R6/lib/libX11.so.6 +#4 0xb7defa88 in XNextEvent () from /usr/X11R6/lib/libX11.so.6 +#5 0x0809b698 in e_alert_show ( + text=0x80a34f0 "This is very bad. Enlightenment has segfaulted.\nThis + is not meant to happen and is likely a + sign of a\nbug in Enlightenment + or the libraries it relies on.\n\nYou can gdb attach to this process + now to try"...) + at e_alert.c:136 +#6 0x0808f706 in e_sigseg_act (x=11, info=0x80a9fb0, data=0x80aa030) + at e_signals.c:54 +#7 <signal handler called> +#8 0xb7d539f8 in select () from /lib/tls/libc.so.6 +#9 0xb7f814ee in _ecore_main_select (timeout=0) + at ecore_main.c:338 +#10 0xb7f819ba in _ecore_main_loop_iterate_internal (once_only=0) + at ecore_main.c:575 +#11 xb7f81a2b in ecore_main_loop_begin () at ecore_main.c:79 +#12 0x08059bb3 in main (argc=1, argv=0xbffff144) at e_main.c:551 +</code> + +As you can see in the stack trace, GDB finds the segfault in libc and pops to the main function in e_main. But it doesn't seem credible to have a bug in libc or x, the important thing is Enlightenment has its own segfault handler which is very explicit on frame 5. + +The e_sigseg_act() function at frame 6 is called directly from the kernel when the program segfaults, meaning enlightenment causes the segfault. So, the segfault comes from the select function (a libc function) at frame 8 called in _e_core_main_select_function at frame 9. + +== Go in a frame == + +So, the reason of segfault seems to be at frame 9, when ''select'' function is called. Let's go to frame 9: + +<code bash> +fr 9 +#9 0xb7f814ee in _ecore_main_select (timeout=0) at ecore_main.c:338 +338 ret = select(max_fd + 1, &rfds, &wfds, &exfds, t); +(gdb) l +333 } +334 } +335 #ifndef WIN32 +336 if (_ecore_signal_count_get()) return -1; +337 #endif +338 ret = select(max_fd + 1, &rfds, &wfds, &exfds, t); +339 if (ret < 0) +340 { +341 if (errno == EINTR) return -1; +342 } +</code> + +The first command **//fr 9//** gives useful information: name of the file, number of the line, the function called, ... The second command **//l//** lists the code around the called function. Another useful command allows to print the variables, the parameters, helping you to find out the problem, a wrong parameter, a null pointer... + +<code bash> +(gdb) p ret +$1 = -4 +(gdb) p rfds +$2 = {__fds_bits = {1280, 0 <repeats 31 times>}} +(gdb) p wfds +$3 = {__fds_bits = {0 <repeats 32 times>}} +(gdb) p exfds +$4 = {__fds_bits = {0 <repeats 32 times>}} +</code> + +GDB is important to start debugging, it will help you to resize the problem even if sometimes is not enough. + +---- + +=== Valgrind === + +Valgrind aims at finding memory problems but for that Enlightenment needs to be run through Valgrind. + +== Prerequisites == + +This tutorial will present 3 different ways to run enlightenment through Valgrind: + + * Remote debugging + * Xephyr invocation + * Xinit invocation + +The easiest way is certainly Xephyr because it allows to target a window on a X server host, sadly Xephyr doesn't yet support OpenGL and any issue that may be related to it will need to use the Xinit version. + +== Remote Debugging == + +Enlightenment_start launcher will handle setting up environment variables, paths, and launching any other required services before Enlightenment starts. Fortunately, there are some options in enlightenment_start that allow to run Enlightenment through Valgrind: + +<code bash> +$enlightenment_start --help +Options: + -valgrind[=MODE] + Run enlightenment from inside valgrind, mode is OR of: + 1 = plain valgrind to catch crashes (default) + 2 = trace children (thumbnailer, efm slaves, ...) + 4 = check leak + 8 = show reachable after processes finish. + all = all of above + -massif + Run enlightenment from inside massif valgrind tool. + -callgrind + Run enlightenment from inside callgrind valgrind tool. + -valgrind-log-file=<FILENAME> + Save valgrind log to file, see valgrind's --log-f +</code> + +First of all, get the IP address of your host machine and connect to it, then +on the distant machine, launch X: + +<code bash> +#launch X on tty1 +sudo X -ac :1 & +</code> + +For example, if you want to check leak and save traces in a log file: + +<code bash> +export DISPLAY=:1 +enlightenment_start -valgrind=4 -valgrind-log-file=log.txt +</code> + +At that point, Enlightenment should have started on your host machine. If the session is closed then the summary of Valgrind should look like: + +<code bash> +==1488== +==1488== HEAP SUMMARY: +==1488== in use at exit: 4,479,487 bytes in 24,302 blocks +==1488== total heap usage: 336,239 allocs, 311,937 frees, 88,068,674 bytes allocated +==1488== +==1488== LEAK SUMMARY: +==1488== definitely lost: 825 bytes in 15 blocks +==1488== indirectly lost: 39 bytes in 2 blocks +==1488== possibly lost: 384 bytes in 1 blocks +==1488== still reachable: 4,478,239 bytes in 24,284 blocks +==1488== suppressed: 0 bytes in 0 blocks +==1488== Rerun with --leak-check=full to see details of leaked memory +==1488== +==1488== For counts of detected and suppressed errors, rerun with: -v +==1488== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0) +</code> + +== Valgrind Invocation - Xinit == + +Create a file called .xinitrc-debug in your home with the following content: + +<code bash> +#!/bin/sh + +ulimit -c unlimited + +log_file="$HOME/enlightenment-xinit-debug-valgrind.log" +#path of you installation +enlightenment_install_path=/usr/local + +#set vars +LD_LIBRARY_PATH="$enlightenment_install_path/lib" +PATH="$enlightenment_install_path/bin:$PATH" + +#log to file +echo "using installation at $enlightenment_install_path" +echo "LD_LIBRARY_PATH=$LD_LIBRARY_PATH" > $log_file +echo "PATH=$enlightenment_install_path/bin: ... " >> $log_file + +#start e with valgrind +$enlightenment_install_path/bin/enlightenment_start -valgrind 2>&1 | tee -a "$log_file" +</code> + +You can now start a debugging session, after X was closed if it is not the case log out: + +<code bash> +/usr/bin/xinit ~/.xinitrc-debug -- :1 -nolisten tcp +</code> + +== Valgrind Invocation - Xephyr == + +Xephyr is a display server implementing the X11 display server protocol which targets a window on a X Server host. So, for this it is important that X is launched, you can even do it in your usual window manager under X. + +Of course, you need to install Xephyr. + +<code bash> +Xephyr -ac -br -noreset -screen 800x600 :1 +</code> + + *ac: disable access control restrictions + *br: create root window with black background + *noreset: don't reset after last client exists + *screen 800x600: Specify screen characteristics + +A black screen should now be displayed, and the interesting thing for us is that you can launch a window manager on it with Valgrind in addition: + +<code bash> +DISPLAY=:1 enlightenment_start -valgrind +</code> \ No newline at end of file --
