[ptxdist] ffmpeg build/effect of ptxdist build environment

[<jon.bird@gd-ms.uk>]

Hi,

I have been attempting to build ffmpeg under ptxdist - which I appreciate is marked as broken but thought I'd have a go anyway.

I managed to build specific version called up by ptxdist (ffmpeg-r12314) however that is too old to suite my purposes so I am using a slightly newer version (from 2011 era). This all sails through quite nicely until the final link point at which it bails out with several hundred unresolved linker errors:

i686-atom-linux-gnu-gcc -Llibavcodec -Llibavdevice -Llibavfilter -Llibavformat -Llibavutil -Llibpostproc -Llibswscale -L/home/jon/projects/ptxdist/platform-i586/sysroot-target/usr/lib -Wl,--as-needed -Wl,--warn-common -Wl,-rpath-link,libpostproc -Wl,-rpath-link,libswscale -Wl,-rpath-link,libavfilter -Wl,-rpath-link,libavdevice -Wl,-rpath-link,libavformat -Wl,-rpath-link,libavcodec -Wl,-rpath-link,libavutil -o ffmpeg_g ffmpeg.o cmdutils.o -lavdevice -lavfilter -lavformat -lavcodec -lswscale -lavutil -L/home/jon/projects/ptxdist/platform-i586/sysroot-target/usr/lib -lSDL -lpthread -lm -pthread -lz -lm
ffmpeg.o: In function `ffmpeg_exit':
ffmpeg.c:(.text+0x673): undefined reference to `avio_close'
ffmpeg.c:(.text+0x67b): undefined reference to `avformat_free_context'
ffmpeg.o: In function `choose_pixel_fmt.isra.3':
...

Looking closely at the linker command line, I can't actually see anything wrong here and indeed the symbols it is after are definitely in the "av" libraries called up. In fact if you invoke this command outside the ptxdist build environment in the relevant build folder (ie. platform-i586/build-target/ffmpeg-0.8) then it works perfectly and creates a working executable.

So it's something inside the ptxdist environment that is causing this. Delving further, I dumped out the environment variables, wrapped it into a script and called it thus:

#!/bin/bash
# env.sh
export PTXCONF_SETUP_KERNELMIRROR=http://www.kernel.org/pub/linux
export PTXCONF_SETUP_ENV_WHITELIST=
export PTXDIST_LIB_DIR=/usr/local/lib/ptxdist-2012.12.1/scripts/lib
export PTXDIST_PATH_PLATFORMS_XLBSP=/home/jon/projects/ptxdist/platforms/xlbsp:/home/jon/projects/ptxdist/configs/i586-qemu/platforms/xlbsp:/usr/local/lib/ptxdist-2012.12.1/platforms/xlbsp:
...
i686-atom-linux-gnu-gcc -Llibavcodec/ -Llibavdevice -Llibavfilter -Llibavformat -Llibavutil ...

then runs as:

env -i ./env.sh

sure enough, it bails with the same linker errors. Stripping back the environment variables one by one the thing that seems to upset it is this:

export PTXDIST_CROSS_LDFLAGS="-L/home/jon/projects/ptxdist/platform-i586/sysroot-target/lib -L/home/jon/projects/ptxdist/platform-i586/sysroot-target/usr/lib -Wl,-rpath-link -Wl,/home/jon/projects/ptxdist/platform-i586/sysroot-target/lib -Wl,-rpath-link -Wl,/home/jon/projects/ptxdist/platform-i586/sysroot-target/usr/lib"

Here is where I'm stumped because this implies to me that the toolchain itself has been built to recognize this (ptxdist specific) environment variable and act on it in some way. Can anyone explain this?

This is all using ptxdist-2012.1, targeting x86.

Thanks,


Jon.

--
Jon Bird, CEng MBCS
Software Engineer
Electronic Systems
General Dynamics United Kingdom Ltd.
Castleham Road, St Leonards on Sea, East Sussex, TN38 9NJ

Telephone: +441424798278
Email: jon.bird@gd-ms.uk
Website: www.generaldynamics.uk.com


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