[FFmpeg-devel] [PATCH] lavf/wavdec.c: Fix unresolved symbols on Mac and VS2015 Update 3

Matt Oliver protogonoi at gmail.com
Fri Dec 16 02:41:21 EET 2016


On 16 December 2016 at 09:54, Hendrik Leppkes <h.leppkes at gmail.com> wrote:

> On Thu, Dec 15, 2016 at 8:43 PM, Matthew Wolenetz <wolenetz at chromium.org>
> wrote:
> >>
> >> This seems like a rather odd issue to be toolchain specific. Can you
> >> please provide a configure command line that would result in a broken
> >> build?
> >
> >
> > I believe the link-time failures occurred with configs like these:
> >
> > IIRC, on Mac, Chromium build hit this with:
> >
> >    -
> >    https://cs.chromium.org/chromium/src/third_party/
> ffmpeg/chromium/config/Chromium/mac/x64/config.h?rcl=0&l=4
> >
> > On Windows, one or both of the following hit this:
> >
> >    -
> >    https://cs.chromium.org/chromium/src/third_party/
> ffmpeg/chromium/config/Chromium/win/ia32/config.h?rcl=0&l=4
> >    -
> >    https://cs.chromium.org/chromium/src/third_party/
> ffmpeg/chromium/config/Chromium/win/x64/config.h?rcl=0&l=4
> >
> > DCE is needed for FFmpeg compilation, this should get fixed by Steve
> >> Lhomme's
> >> configure patch.
> >> I find it hard to understand why wavdec.c would be the only file
> >> showing this issue...
> >
> >
> > Notably, windows still hit this (VS2015 Update 3 19.00.24213.1) *even
> with
> > -O2.*
> >
> >
>
> You are using a custom build system, there is no way to verify any
> issues for us unless you can provide a configure commandline that
> fails on our own build-system.
>
> The patches do look like they are trying to avoid the use of DCE - and
> as Carl already pointed out, quite a lot of our code relies on DCE
> being performed by the compiler/linker, so fixing it in one or two
> isolated spots wouldn't really fix anything but your own customized
> specific build, and make our code-base less consistent within itself.
> DCE generally works fine with Visual Studio, and I do not know of any
> configure setup that makes it fail - of course with the exception of
> using --disable-optimizations, as that turns everything of for MSVC
> right now, including DCE, which makes the build impossible.


Debug builds and lto still have issues with DCE with msvc and icl. Also in
an original email that mentioned a similar problem
https://lists.ffmpeg.org/pipermail/ffmpeg-devel/2016-April/193454.html
people also mentioned issues with clang and gold compilers due to DCE. As
per the linked email thread though I dont think adding patches to fix 1 or
2 cases of DCE issues should be excepted, instead we need to work out a
global solution to the issues with DCE.


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