[FFmpeg-devel] [PATCH] Add -fno-common to PE32 CFLAGS

[Ramiro Polla]

2009/4/13 M?ns Rullg?rd <mans at mansr.com>:
> Ramiro Polla <ramiro.polla at gmail.com> writes:
>> On Mon, Apr 13, 2009 at 5:31 PM, Baptiste Coudurier
>> <baptiste.coudurier at gmail.com> wrote:
>>> On 4/13/2009 12:48 PM, Baptiste Coudurier wrote:
>>>> On 4/8/2009 6:42 PM, Ramiro Polla wrote:
>>>>> Some time ago Art Clarke sent a patch to unconditionally add
>>>>> -fno-common to mingw32 builds because of a bug in GCC. Instead of
>>>>> applying the patch, the documentation was updated to reflect this bug
>>>>> and the workaround.
>>>>>
>>>>> The bug details can be found here:
>>>>> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37216
>>>>>
>>>>> I finally took some time to investigate what combination of
>>>>> gcc+binutils triggers the bug. Just like Brian Dessent mentions in
>>>>> comment #6, the bug appears with binutils starting November 2007. The
>>>>> gcc version doesn't matter as long as it puts data in .comm. binutils
>>>>> 2.18 doesn't show this bug, but it has other shortcomings which make
>>>>> it not fit for building FFmpeg.
>>>>>
>>>>> With current mingw32 binutils floating around the web, all builds will
>>>>> crash at some point in some optimizations (maybe Baptiste can give us
>>>>> a sample that really crashes, I haven't seen them yet, but there are
>>>>> lots of reports).
>>>>>
>>>>> So is it ok to unconditionally include this flag with attached patch
>>>>> (and a very descriptive log message) before binutils is fixed?
>>>>
>>>> Yes, please many bug reports on windows because of this, shared libs are
>>>> just broken without it.
>>>>
>>>> You might remove it for OS/2 though according to Dave Yeo.
>>>
>>> I think you could also only add it for shared libs. I don't recall it
>>> was needed for static builds.
>>
>> The bug on gcc+binutils shows itself independent of being in a .dll or
>> in the .exe itself, so I assume this bug doesn't appear on static
>> FFmpeg builds purely by luck.
>>
>> I updated the patch removing the flag from OS/2 as suggested by Dave Yeo.
>>
>> The commit message would be:
>> "win32, dos: Work around a bug in the GNU toolchain.
>> The bug[1] is exposed when gcc decides to put some data in a common
>> section (i.e. data that will be used by more than one object). It will
>> suggest the data to be aligned, but binutils >= 2.19 will fail to
>> properly align it. Thus if the data requires any alignment greater
>> than 4, the application will crash.
>> The workaround prevents gcc from putting data in a common section,
>> instead putting it in a properly aligned section.
>>
>> [1] http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37216"
>>
>> I'll commit this if I get an explicit ok from the build system
>> maintainers, because I don't want them bugging us later on if they
>> don't like this hack. And if they're not ok with it, then please
>> suggest an alternative solution.
>>
>> Ramiro Polla
>>
>> Index: configure
>> ===================================================================
>> --- configure (revision 18499)
>> +++ configure (working copy)
>> @@ -1634,6 +1634,7 @@
>> ? ? ? ? ?SHFLAGS='-shared -Wl,--output-def,$$(@:$(SLIBSUF)=.def) -Wl,--out-implib,$(SUBDIR)lib$(SLIBNAME:$(SLIBSUF)=.dll.a) -Wl,--enable-runtime-pseudo-reloc -Wl,--enable-auto-image-base'
>> ? ? ? ? ?objformat="win32"
>> ? ? ? ? ?enable dos_paths
>> + ? ? ? ?check_cflags -fno-common
>> ? ? ? ? ?if ! enabled x86_64; then
>> ? ? ? ? ? ? ?check_cpp_condition _mingw.h "(__MINGW32_MAJOR_VERSION > 3) || (__MINGW32_MAJOR_VERSION == 3 && __MINGW32_MINOR_VERSION >= 15)" ||
>> ? ? ? ? ? ? ? ? ?die "ERROR: MinGW runtime version must be >= 3.15."
>> @@ -1652,6 +1653,7 @@
>> ? ? ? ? ?SHFLAGS='-shared -Wl,--enable-auto-image-base'
>> ? ? ? ? ?objformat="win32"
>> ? ? ? ? ?enable dos_paths
>> + ? ? ? ?check_cflags -fno-common
>> ? ? ? ? ?;;
>> ? ? ?*-dos|freedos|opendos)
>> ? ? ? ? ?disable ffplay ffserver
>> @@ -1659,6 +1661,7 @@
>> ? ? ? ? ?network_extralibs="-lsocket"
>> ? ? ? ? ?objformat="coff"
>> ? ? ? ? ?enable dos_paths
>> + ? ? ? ?check_cflags -fno-common
>> ? ? ? ? ?;;
>> ? ? ?linux)
>> ? ? ? ? ?enable dv1394
>
> OK

Applied.