[FFmpeg-devel] [PATCH 1/3] configure: Force mingw's ld to keep the reloc section

[Michael Niedermayer]

On Thu, Mar 10, 2016 at 07:57:53PM +0100, Hendrik Leppkes wrote:
> On Mon, Sep 21, 2015 at 6:41 AM, Alex Smith <alex.smith at warpsharp.info> wrote:
> > From: Alex Smith <alex.smith at warpsharp.info>
> >
> > Binutils will always strip the relocation information from executable
> > files even if it needs it (dynamicbase/ASLR).  We can work around this
> > by using the pic-executable flag combined with setting the correct entry
> > point since apparently ld forgets what that should be.  This problem
> > affects both 32 and 64-bit mingw-w64.
> >
> > We can combine the nxcompat/dynamicbase check because they were added to
> > binutils at the same time.
> >
> > Signed-off-by: Alex Smith <alex.smith at warpsharp.info>
> >
> > Conflicts:
> >         configure
> > ---
> >  configure | 13 +++++++++++--
> >  1 file changed, 11 insertions(+), 2 deletions(-)
> >
> > diff --git a/configure b/configure
> > index d2a25bb..d6ab35a 100755
> > --- a/configure
> > +++ b/configure
> > @@ -4367,8 +4367,6 @@ case $target_os in
> >              LIBTARGET=arm-wince
> >          fi
> >          enabled shared && ! enabled small && check_cmd $windres --version && enable gnu_windres
> > -        check_ldflags -Wl,--nxcompat
> > -        check_ldflags -Wl,--dynamicbase
> >          enabled x86_32 && check_ldflags -Wl,--large-address-aware
> >          shlibdir_default="$bindir_default"
> >          SLIBPREF=""
> > @@ -4392,6 +4390,17 @@ case $target_os in
> >          objformat="win32"
> >          ranlib=:
> >          enable dos_paths
> > +        check_ldflags -Wl,--nxcompat,--dynamicbase
> > +        # Lets work around some stupidity in binutils.
> > +        # ld will strip relocations from executables even though we need them
> > +        # for dynamicbase (ASLR).  Using -pie does retain the reloc section
> > +        # however ld then forgets what the entry point should be (oops) so we
> > +        # have to manually (re)set it.
> > +        if enabled x86_32; then
> > +            add_ldexeflags -Wl,--pic-executable,-e,_mainCRTStartup
> > +        elif enabled x86_64; then
> > +            add_ldexeflags -Wl,--pic-executable,-e,mainCRTStartup
> > +        fi
> >          ;;
> >      win32|win64)
> >          disable symver
> 
> This patch (the relocations part) broke debugging mingw-w64 ffmpeg
> builds with gdb, you can't set breakpoints anymore when its applied.
> It should either be reverted or made dependent on
> --enable/disable-debug (I would favor the first, honestly, since its a
> rather ugly hack in itself).

as i was the one applying it IIRC, i should probably comment ...
iam not against this being partially or fully revered/mode conditional
if it causes more problems than it does good.




> 
> Did the binutils/mingw guys ever comment anything useful on this issue?
> 
> - Hendrik
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-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

When the tyrant has disposed of foreign enemies by conquest or treaty, and
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