[Buildroot] [PATCH] ffmpeg: improve linking avoiding -ldrm to be appended when -lavutil is linked

[Giulio Benetti <giulio.benetti@micronovasrl.com>]

Il 30/01/2019 17:01, Giulio Benetti ha scritto:
> Upstream ffmpeg patch[1] has a drawback. Linking against libavutil
> results in appending -ldrm to library list in linker command tail, but
> in shared linking this is no needed at all since shared linking is
> transparent about library dependecies, hence -ldrm in this case is not
> needed.
> 
> Add patch to avoid this behaviour by:
> - Introducing new variable "privatelibs" that is assigned to
>    "Libs.private:" when creating various .pc files.
> - Move $LIBDRM from extralibs_avutil to privatelibs_avutil
> 
> [1]
> https://git.ffmpeg.org/gitweb/ffmpeg.git/commit/c50dc77ac708e98d02da7c422a6b9cbf9f565aa5
> 
> Signed-off-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
> ---
>   ...BDRM-to-Libs.private-instead-of-Libs.patch | 59 +++++++++++++++++++
>   1 file changed, 59 insertions(+)
>   create mode 100644 package/ffmpeg/0002-configure-add-LIBDRM-to-Libs.private-instead-of-Libs.patch
> 
> diff --git a/package/ffmpeg/0002-configure-add-LIBDRM-to-Libs.private-instead-of-Libs.patch b/package/ffmpeg/0002-configure-add-LIBDRM-to-Libs.private-instead-of-Libs.patch
> new file mode 100644
> index 0000000000..f19c74f228
> --- /dev/null
> +++ b/package/ffmpeg/0002-configure-add-LIBDRM-to-Libs.private-instead-of-Libs.patch
> @@ -0,0 +1,59 @@
> +From e34be93d478ad510960d03549572805a0430144c Mon Sep 17 00:00:00 2001
> +From: Giulio Benetti <giulio.benetti@micronovasrl.com>
> +Date: Sun, 21 Oct 2018 22:43:39 +0200
> +Subject: [PATCH] configure: add LIBDRM to Libs.private instead of Libs
> +
> +Currently LIBDRM is appended to Libs: in libavutil.pc. This causes
> +every program linking with avutil to link with -ldrm in both shared and
> +static linking cases. In shared linking case it makes no sense, since
> +-ldrm is a dependency of libavutil and is transparent while linking with
> +libavutil
> +
> +- Add privatelibs_avutil variable for explicit private libraries to be
> +  appended to Libs.private:
> +- Add $LIBDRM to privatelibs_avutil.
> +
> +Signed-off-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
> +---
> + configure                     | 3 ++-
> + ffbuild/pkgconfig_generate.sh | 3 ++-
> + 2 files changed, 4 insertions(+), 2 deletions(-)
> +
> +diff --git a/configure b/configure
> +index 9fe7760822..0996d8a85d 100755
> +--- a/configure
> ++++ b/configure
> +@@ -7096,7 +7096,8 @@ source_path=${source_path}
> + LIBPREF=${LIBPREF}
> + LIBSUF=${LIBSUF}
> +
> +-extralibs_avutil="$LIBRT $LIBDRM $LIBM"
> ++extralibs_avutil="$LIBRT $LIBM"
> ++privatelibs_avutil="$LIBDRM"
> + extralibs_avcodec="$extralibs"
> + extralibs_avformat="$extralibs"
> + extralibs_avdevice="$extralibs"
> +diff --git a/ffbuild/pkgconfig_generate.sh b/ffbuild/pkgconfig_generate.sh
> +index e5de6716d2..b86486a107 100755
> +--- a/ffbuild/pkgconfig_generate.sh
> ++++ b/ffbuild/pkgconfig_generate.sh
> +@@ -13,6 +13,7 @@ name=lib${shortname}
> + fullname=${name}${build_suffix}
> + comment=$2
> + libs=$(eval echo \$extralibs_${shortname})
> ++privatelibs=$(eval echo \$privatelibs_${shortname})
> + deps=$(eval echo \$${shortname}_deps)
> +
> + for dep in $deps; do
> +@@ -39,7 +40,7 @@ Requires: $($shared || echo $requires)
> + Requires.private: $($shared && echo $requires)
> + Conflicts:
> + Libs: -L\${libdir} $rpath -l${fullname#lib} $($shared || echo $libs)
> +-Libs.private: $($shared && echo $libs)
> ++Libs.private: $($shared && echo $libs) ${privatelibs}
> + Cflags: -I\${includedir}
> + EOF
> +
> +--
> +2.17.1
> +
> 

This patch applied to 3.4.x version and wasn't vital since it didn't 
create build failure.
FFmpeg will upstream patches only for security bugs, so this patch 
doesn't make sense.
I set it rejected on Patchwork.

Best regards
-- 
Giulio Benetti
CTO

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