I uploaded a new patch (v3) that addresses these concerns. On Thu, Feb 27, 2025 at 5:14 PM Michael Niedermayer <mich...@niedermayer.cc> wrote:
> On Wed, Feb 26, 2025 at 07:44:37PM +0000, Pranav Kant via ffmpeg-devel > wrote: > > By default, all globals in C/C++ compiled by clang are allocated > > in non-large data sections. See [1] for background on code models. > > For PIC (Position independent code), this is fine as long as binary is > > small but as binary size increases, users maybe want to use medium/large > > code models (-mcmodel=medium) which moves data in to large sections. > > As data in these large sections cannot be accessed using PIC code > > anymore (as it may be too far away), compiler ends up using a different > > instruction sequence when building C/C++ code -- using GOT to access > > these globals (which can be relaxed by linker at link time if binary > > ends up being smaller). However, assembly files continue to access these > > globals defined in C/C++ files using older (and invalid instruction > > sequence). So, we mark all such globals with an attribute that forces > > them to be allocated in small sections allowing them to validly be > > accessed from the assembly code. > > > > This patch should not have any affect on builds that use small code > > model, which is the default mode. > > > > [1] > https://eli.thegreenplace.net/2012/01/03/understanding-the-x64-code-models > > > > Signed-off-by: Pranav Kant <p...@google.com> > > --- > > libavcodec/ac3dsp.c | 2 ++ > > libavcodec/cabac.c | 2 ++ > > libavcodec/x86/constants.c | 8 ++++++++ > > libavutil/attributes_internal.h | 15 +++++++++++++++ > > 4 files changed, 27 insertions(+) > > This produces many warnings: > > CC libavcodec/svq1.o > In file included from libavcodec/svq1.h:40, > from libavcodec/svq1.c:35: > ./libavutil/attributes_internal.h:43:5: warning: "ARCH_X86_64" is not > defined, evaluates to 0 [-Wundef] > 43 | #if ARCH_X86_64 && defined(__ELF__) && __has_attribute(model) > | ^~~~~~~~~~~ > > [...] > > -- > Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB > > If you fake or manipulate statistics in a paper in physics you will never > get a job again. > If you fake or manipulate statistics in a paper in medicin you will get > a job for life at the pharma industry. > _______________________________________________ > ffmpeg-devel mailing list > ffmpeg-devel@ffmpeg.org > https://ffmpeg.org/mailman/listinfo/ffmpeg-devel > > To unsubscribe, visit link above, or email > ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe". > _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
