Debug - Revision history

Courmisch: /* How to make a back-trace */

2020-12-17T10:04:29Z

How to make a back-trace

← Older revision		Revision as of 10:04, 17 December 2020
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	(gdb) thread apply all bt		(gdb) thread apply all bt
	</pre>		</pre>

			There is also a dedicated [[Tutorial for gdb debug under Win32\|tutorial for GDB on Windows]].

	=== What does it look like? ===		=== What does it look like? ===

Courmisch: /* How to make a back-trace */

2020-12-17T10:01:48Z

How to make a back-trace

← Older revision		Revision as of 10:01, 17 December 2020
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	This depends heavily on which debugger you use, and which platform you run.		This depends heavily on which debugger you use, and which platform you run.
	The most common choice is the GNU debugger, a.k.a. <code>gdb</code>		The most common choice is the GNU debugger, a.k.a. <code>gdb</code>:

	<pre>		<pre>

Courmisch: /* What does it look like? */

2020-12-17T10:01:33Z

What does it look like?

← Older revision		Revision as of 10:01, 17 December 2020
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	This is a debug-friendly back-trace:		This is a debug-friendly back-trace:
	''Program received signal SIGSEGV, Segmentation fault.''		<pre>
	''[Switching to Thread 0xb22e9b90 (LWP 17982)]''		Program received signal SIGSEGV, Segmentation fault.
	''0xb7a965e8 in CDDAFormatTitle (p_access=0x842afe0, i_track=99 'c') at info.c:630''		[Switching to Thread 0xb22e9b90 (LWP 17982)]
	''630 info.c: No such file or directory.''		0xb7a965e8 in CDDAFormatTitle (p_access=0x842afe0, i_track=99 'c') at info.c:630
	'' in info.c''		630 info.c: No such file or directory.
	''(gdb) bt full''		in info.c
			(gdb) bt full
	#0 0xb7a965e8 in CDDAFormatTitle (p_access=0x842afe0, i_track=99 'c') at		#0 0xb7a965e8 in CDDAFormatTitle (p_access=0x842afe0, i_track=99 'c') at
	info.c:630		info.c:630
Line 73:		Line 74:
	#10 0xb7ddb09e in clone () from /lib/libc.so.6		#10 0xb7ddb09e in clone () from /lib/libc.so.6
	No symbol table info available.		No symbol table info available.
			</pre>

	And that is a not debug-friendly back-trace, which is indeed useless for developers:		And that is a not debug-friendly back-trace, which is indeed useless for developers:
	''Program received signal SIGSEGV, Segmentation fault.''		<pre>
	''[Switching to Thread -1342661712 (LWP 8792)]''		Program received signal SIGSEGV, Segmentation fault.
	''0xb7db65ab in __module_Need () from /usr/lib/libvlc.so.0''		[Switching to Thread -1342661712 (LWP 8792)]
	''(gdb) bt''		0xb7db65ab in __module_Need () from /usr/lib/libvlc.so.0
			(gdb) bt
	#0 0xb7db65ab in __module_Need () from /usr/lib/libvlc.so.0		#0 0xb7db65ab in __module_Need () from /usr/lib/libvlc.so.0
	#1 0xb7ec5c34 in ?? () from /usr/lib/libvlc.so.0		#1 0xb7ec5c34 in ?? () from /usr/lib/libvlc.so.0
Line 92:		Line 95:
	#10 0x00000003 in ?? ()		#10 0x00000003 in ?? ()
	#11 0x00000000 in ?? ()		#11 0x00000000 in ?? ()
			</pre>

	=== Is a backtrace enough to debug? ===		=== Is a backtrace enough to debug? ===

Courmisch: /* How to make a back-trace */

2020-12-17T10:00:02Z

How to make a back-trace

← Older revision		Revision as of 10:00, 17 December 2020
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	The most common choice is the GNU debugger, a.k.a. <code>gdb</code>		The most common choice is the GNU debugger, a.k.a. <code>gdb</code>

	~~{{{~~		<pre>
	# gdb --args ./vlc -Irc -vv		# gdb --args ./vlc -Irc -vv
	...		...
Line 32:		Line 32:
	...		...
	(gdb) thread apply all bt		(gdb) thread apply all bt
	~~}}}~~		</pre>

	=== What does it look like? ===		=== What does it look like? ===

Courmisch at 09:59, 17 December 2020

2020-12-17T09:59:43Z

← Older revision		Revision as of 09:59, 17 December 2020
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	~~When~~ compiling {{VLC}}, you can ~~compile~~ a debug ~~binary~~ using <code>--enable-debug</code> on the ./configure script.		While compiling {{VLC}}, you can make a debug build using <code>--enable-debug</code> on the ./configure script command line.

	Those debug ~~facts~~ are common to every programs, not ~~only~~ VLC.		Those debug factoids are common to every programs, not just VLC.

	== What it is used for ==		== 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~~		Of course, binaries compiled in debug mode will or should more-or-less behave like the release ones. Differences include:
	* ~~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~~		* Invalid internal states may cause assertion failure and crash the program with an explicit error, while the program would continue running in release version (and possibly crash later in weirder manner).
	* ~~binary backtraces~~ are meaningful in this mode since symbols are embedded in it.		* Binary back-traces are meaningful and usually more legible in this mode since symbols are embedded in the binaries.

			As such, the main purpose is for developers to make debug-friendly binaries and investigate crashes and other bugs.

	~~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 noted above, you basically just have to add <code>CFLAGS="-g" CXXFLAGS="-g" --enable-debug</code> parameters at the [[configure\|./configure]] stage.

	~~== How~~ to ~~enable it~~ ==		For stepping into code, better is to do <code>CFLAGS="-g -Og" CXXFLAGS="-g -Og"</code> also add <code>--disable-optimizations</code>. For more information see [[VLC configure help]].

	~~As said above, you basically just have to add <code>CFLAGS~~="-~~g" CXXFLAGS~~=~~"-g" --enable-debug</code> parameters at the [[configure\|./configure]] stage.~~		== Back-traces ==

	~~For stepping into code, better~~ is ~~to do <code>CFLAGS="-g -Og" CXXFLAGS="-g -Og"</code> also add <code>--disable-optimizations</code> and not use <code>--enable-release</code>. Replace <code>-Og</code> with <code>~~-~~O0</code> to prevent compiler from optimizing out variables. For more information see [[VLC configure help]]~~.		A back-trace is a snapshot of the process call-flow at a given time during execution.

	== ~~Backtraces~~ ==		=== How to make a back-trace ===

	~~A backtrace~~ is a ~~snapshot of~~ a ~~process at the time it is about to crash~~.		This depends heavily on which debugger you use, and which platform you run.
			The most common choice is the GNU debugger, a.k.a. <code>gdb</code>

			{{{
			# gdb --args ./vlc -Irc -vv
			...
			(gdb) run
			...
			(gdb) thread apply all bt
			}}}

	=== What does it look like? ===		=== What does it look like? ===

	~~Here~~ is a debug-friendly ~~backtrace~~:		This is a debug-friendly back-trace:
	''Program received signal SIGSEGV, Segmentation fault.''		''Program received signal SIGSEGV, Segmentation fault.''
	''[Switching to Thread 0xb22e9b90 (LWP 17982)]''		''[Switching to Thread 0xb22e9b90 (LWP 17982)]''
Line 63:		Line 74:
	No symbol table info available.		No symbol table info available.

	And ~~here~~ is a not debug-friendly ~~backtrace~~, ~~unuseful in fact.~~		And that is a not debug-friendly back-trace, which is indeed useless for developers:
	''Program received signal SIGSEGV, Segmentation fault.''		''Program received signal SIGSEGV, Segmentation fault.''
	''[Switching to Thread -1342661712 (LWP 8792)]''		''[Switching to Thread -1342661712 (LWP 8792)]''
Line 81:		Line 92:
	#10 0x00000003 in ?? ()		#10 0x00000003 in ?? ()
	#11 0x00000000 in ?? ()		#11 0x00000000 in ?? ()


	~~As you can see, developers can't cope with last backtrace.~~

	=== Is a backtrace enough to debug? ===		=== Is a backtrace enough to debug? ===
Line 91:		Line 99:

	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.		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.



	== See also ==		== See also ==

DoesItReallyMatter: +:Category:Building

2019-03-19T09:03:55Z

+Category:Building

← Older revision		Revision as of 09:03, 19 March 2019
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	* [[Tutorial for gdb debug under Win32\|Tutorial for GDB with Win32]]		* [[Tutorial for gdb debug under Win32\|Tutorial for GDB with Win32]]

			[[Category:Building]]
	[[Category:Coding]]		[[Category:Coding]]

Stephane-gourichon-lpad: Replace `-Og` with `-O0` to prevent compiler from optimizing out variables.

2017-03-10T14:55:22Z

Replace <code>-Og</code> with <code>-O0</code> to prevent compiler from optimizing out variables.

← Older revision		Revision as of 14:55, 10 March 2017
Line 16:		Line 16:
	As said above, you basically just have to add <code>CFLAGS="-g" CXXFLAGS="-g" --enable-debug</code> parameters at the [[configure\|./configure]] stage.		As said above, you basically just have to add <code>CFLAGS="-g" CXXFLAGS="-g" --enable-debug</code> parameters at the [[configure\|./configure]] stage.

	For stepping into code, better is to do <code>CFLAGS="-g -Og" CXXFLAGS="-g -Og"</code> also add <code>--disable-optimizations</code> and not use <code>--enable-release</code>. For more information see [[VLC configure help]].		For stepping into code, better is to do <code>CFLAGS="-g -Og" CXXFLAGS="-g -Og"</code> also add <code>--disable-optimizations</code> and not use <code>--enable-release</code>. Replace <code>-Og</code> with <code>-O0</code> to prevent compiler from optimizing out variables. For more information see [[VLC configure help]].

	== Backtraces ==		== Backtraces ==

Stephane-gourichon-lpad: Fix instructions about getting a meaningul backtrace. Not sure --disable-optimizations has any effect at all.

2017-03-10T12:54:24Z

Fix instructions about getting a meaningul backtrace. Not sure --disable-optimizations has any effect at all.

← Older revision		Revision as of 12:54, 10 March 2017
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	== How to enable it ==		== How to enable it ==

	As said above, you ~~basicly~~ just have to add <code>--enable-debug</code> ~~parameter~~ at the [[configure\|./configure]] stage. better is to also add <code>--disable-optimizations</code> and not use <code>--enable-release</code>.		As said above, you basically just have to add <code>CFLAGS="-g" CXXFLAGS="-g" --enable-debug</code> parameters at the [[configure\|./configure]] stage.

			For stepping into code, better is to do <code>CFLAGS="-g -Og" CXXFLAGS="-g -Og"</code> also add <code>--disable-optimizations</code> and not use <code>--enable-release</code>. For more information see [[VLC configure help]].

	== Backtraces ==		== Backtraces ==

Corbax: /* See also */

2013-10-01T12:53:47Z

Corbax: /* See also */

2013-10-01T12:46:05Z

← Older revision		Revision as of 12:53, 1 October 2013
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	== See also ==		== See also ==

	* [[~~Report_Bugs~~]]		* [[Report Bugs]]
	* VLC_report
	* [[Tutorial for gdb debug under Win32\|Tutorial for GDB with Win32]]		* [[Tutorial for gdb debug under Win32\|Tutorial for GDB with Win32]]

	[[Category:Coding]]		[[Category:Coding]]

← Older revision		Revision as of 12:46, 1 October 2013
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	== See also ==		== See also ==

	* ~~Report_bugs~~		* [[Report_Bugs]]
	* VLC_report		* VLC_report
	* [[Tutorial for gdb debug under Win32\|Tutorial for GDB with Win32]]		* [[Tutorial for gdb debug under Win32\|Tutorial for GDB with Win32]]

	[[Category:Coding]]		[[Category:Coding]]

Debug - Revision history

Courmisch: /* How to make a back-trace */

Courmisch: /* How to make a back-trace */

Courmisch: /* What does it look like? */

Courmisch: /* How to make a back-trace */

Courmisch at 09:59, 17 December 2020

DoesItReallyMatter: +:Category:Building

Stephane-gourichon-lpad: Replace -Og with -O0 to prevent compiler from optimizing out variables.

Stephane-gourichon-lpad: Fix instructions about getting a meaningul backtrace. Not sure --disable-optimizations has any effect at all.

Corbax: /* See also */

Corbax: /* See also */

Stephane-gourichon-lpad: Replace `-Og` with `-O0` to prevent compiler from optimizing out variables.