Debug
When compiling VLC media player, you can compile a debug binary using --enable-debug on the ./configure script.
Those debug facts are common to every programs, not only VLC.
Contents |
What it is used for
Of course, the binary compiled in debug mode will or should behave like the release one (more or less). Differences are
- developers can cause VLC to crash when it reached a suspicious state for development purpose, while release version will not in the same suspicious state
- binary backtraces are meaningful in this mode since symbols are embedded in it.
So its main usage is for developers to use debug-friendly binaries and to reproduce a crash and get its backtrace.
How to enable it
As said above, you basicly just have to add --enable-debug parameter at the ./configure stage. better is to also add --disable-optimizations and not use --enable-release.
Backtraces
A backtrace is a snapshot of a process at the time it is about to crash.
What does it look like?
Here is a debug-friendly backtrace:
Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0xb22e9b90 (LWP 17982)]
0xb7a965e8 in CDDAFormatTitle (p_access=0x842afe0, i_track=99 'c') at info.c:630
630 info.c: No such file or directory.
in info.c
(gdb) bt full
#0 0xb7a965e8 in CDDAFormatTitle (p_access=0x842afe0, i_track=99 'c') at
info.c:630
psz_name = <value optimized out>
config_varname = <value optimized out>
p_cdda = <value optimized out>
psz_mrl = 0x8277238 "cddax:///dev/sr0@T99"
#1 0xb7a94b0f in CDDAReadBlocks (p_access=0x842afe0) at access.c:264
psz_title = <value optimized out>
go_on = <value optimized out>
p_block = <value optimized out>
p_cdda = (cdda_data_t *) 0x84323c0
i_blocks = 20
__func__ = "CDDAReadBlocks"
[...]
#6 0xb6acfe9c in Demux (p_demux=0x833dcb0) at ../../include/vlc_stream.h:189
p_sys = (demux_sys_t *) 0x842eca8
i_pos = <value optimized out>
p_block = (block_t *) 0x859f380
#7 0xb7f34bae in MainLoop (p_input=0x8429c08) at input/input.c:538
b_force_update = 0
i_ret = <value optimized out>
i_type = 138588128
val = {i_int = 1064861644, b_b..........= 0 '\0', h = 0 '\0'}}
i_intf_update = 1214500117823853
#8 0xb7f362b2 in Run (p_input=0x8429c08) at input/input.c:444
No locals.
#9 0xb7e7917b in start_thread () from /lib/libpthread.so.0
No symbol table info available.
#10 0xb7ddb09e in clone () from /lib/libc.so.6
No symbol table info available.
And here is a not debug-friendly backtrace, unuseful in fact.
Program received signal SIGSEGV, Segmentation fault. [Switching to Thread -1342661712 (LWP 8792)] 0xb7db65ab in __module_Need () from /usr/lib/libvlc.so.0 (gdb) bt #0 0xb7db65ab in __module_Need () from /usr/lib/libvlc.so.0 #1 0xb7ec5c34 in ?? () from /usr/lib/libvlc.so.0 #2 0xb5487553 in ?? () from /usr/lib/vlc/stream_out/libstream_out_transcode_plugin.so #3 0x00000009 in ?? () #4 0xb7ec3c74 in ?? () from /usr/lib/libvlc.so.0 #5 0x0854bef8 in ?? () #6 0x08525a00 in ?? () #7 0xb7efaf04 in ?? () from /usr/lib/libvlc.so.0 #8 0xb7dce493 in __vlc_object_release () from /usr/lib/libvlc.so.0 #9 0x0000006f in ?? () #10 0x00000003 in ?? () #11 0x00000000 in ?? ()
As you can see, developers can't cope with last backtrace.
Is a backtrace enough to debug?
It is not enough for someone else than you to fix a bug. At least, you really should describe what you were doing, how to reproduce the bug if you can, etc.
If you try to fix a bug with someone else or if you are asking help on your backtrace, better is really to use an up-to-date VLC source-code. Otherwise, say so and maybe give the commit ID/VLC tag you are working on.
