I added it to attributes_internal.h. The existing attribute in attributes_internal.h (attribute_visibility_hidden) is also being used with DECLARE_ALIGNED macros (see libavcodec/sbrdsp_template.c). My new macro is similar in nature.
On Wed, Feb 26, 2025 at 11:44 AM Pranav Kant <p...@google.com> 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(+) > > diff --git a/libavcodec/ac3dsp.c b/libavcodec/ac3dsp.c > index 730fa70fff..d16b6c24c3 100644 > --- a/libavcodec/ac3dsp.c > +++ b/libavcodec/ac3dsp.c > @@ -25,6 +25,7 @@ > > #include "config.h" > #include "libavutil/attributes.h" > +#include "libavutil/attributes_internal.h" > #include "libavutil/common.h" > #include "libavutil/intmath.h" > #include "libavutil/mem_internal.h" > @@ -104,6 +105,7 @@ static void ac3_update_bap_counts_c(uint16_t > mant_cnt[16], uint8_t *bap, > mant_cnt[bap[len]]++; > } > > +attribute_mcmodel_small > DECLARE_ALIGNED(16, const uint16_t, ff_ac3_bap_bits)[16] = { > 0, 0, 0, 3, 0, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 16 > }; > diff --git a/libavcodec/cabac.c b/libavcodec/cabac.c > index 7d41cd2ae6..b8c6db29a2 100644 > --- a/libavcodec/cabac.c > +++ b/libavcodec/cabac.c > @@ -24,11 +24,13 @@ > * Context Adaptive Binary Arithmetic Coder. > */ > > +#include "libavutil/attributes_internal.h" > #include "libavutil/error.h" > #include "libavutil/mem_internal.h" > > #include "cabac.h" > > +attribute_mcmodel_small > DECLARE_ASM_ALIGNED(1, const uint8_t, ff_h264_cabac_tables)[512 + 4*2*64 > + 4*64 + 63] = { > 9,8,7,7,6,6,6,6,5,5,5,5,5,5,5,5, > 4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4, > diff --git a/libavcodec/x86/constants.c b/libavcodec/x86/constants.c > index bc7f2b17b8..347b7dd1d3 100644 > --- a/libavcodec/x86/constants.c > +++ b/libavcodec/x86/constants.c > @@ -18,17 +18,21 @@ > * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA > 02110-1301 USA > */ > > +#include "libavutil/attributes_internal.h" > #include "libavutil/mem_internal.h" > #include "libavutil/x86/asm.h" // for xmm_reg > #include "constants.h" > > +attribute_mcmodel_small > DECLARE_ALIGNED(32, const ymm_reg, ff_pw_1) = { > 0x0001000100010001ULL, 0x0001000100010001ULL, > > 0x0001000100010001ULL, 0x0001000100010001ULL }; > DECLARE_ALIGNED(32, const ymm_reg, ff_pw_2) = { > 0x0002000200020002ULL, 0x0002000200020002ULL, > > 0x0002000200020002ULL, 0x0002000200020002ULL }; > DECLARE_ASM_ALIGNED(16, const xmm_reg, ff_pw_3) = { > 0x0003000300030003ULL, 0x0003000300030003ULL }; > +attribute_mcmodel_small > DECLARE_ASM_ALIGNED(32, const ymm_reg, ff_pw_4) = { > 0x0004000400040004ULL, 0x0004000400040004ULL, > > 0x0004000400040004ULL, 0x0004000400040004ULL }; > +attribute_mcmodel_small > DECLARE_ASM_ALIGNED(16, const xmm_reg, ff_pw_5) = { > 0x0005000500050005ULL, 0x0005000500050005ULL }; > DECLARE_ALIGNED(16, const xmm_reg, ff_pw_8) = { > 0x0008000800080008ULL, 0x0008000800080008ULL }; > DECLARE_ASM_ALIGNED(16, const xmm_reg, ff_pw_9) = { > 0x0009000900090009ULL, 0x0009000900090009ULL }; > @@ -49,6 +53,7 @@ DECLARE_ALIGNED(32, const ymm_reg, ff_pw_256) = { > 0x0100010001000100ULL, 0x010 > DECLARE_ALIGNED(32, const ymm_reg, ff_pw_512) = { > 0x0200020002000200ULL, 0x0200020002000200ULL, > > 0x0200020002000200ULL, 0x0200020002000200ULL }; > DECLARE_ALIGNED(16, const xmm_reg, ff_pw_1019) = { > 0x03FB03FB03FB03FBULL, 0x03FB03FB03FB03FBULL }; > +attribute_mcmodel_small > DECLARE_ALIGNED(32, const ymm_reg, ff_pw_1023) = { > 0x03ff03ff03ff03ffULL, 0x03ff03ff03ff03ffULL, > > 0x03ff03ff03ff03ffULL, 0x03ff03ff03ff03ffULL}; > DECLARE_ALIGNED(32, const ymm_reg, ff_pw_1024) = { > 0x0400040004000400ULL, 0x0400040004000400ULL, > @@ -66,13 +71,16 @@ DECLARE_ALIGNED(32, const ymm_reg, ff_pw_m1) = { > 0xFFFFFFFFFFFFFFFFULL, 0xFFF > > DECLARE_ALIGNED(32, const ymm_reg, ff_pb_0) = { > 0x0000000000000000ULL, 0x0000000000000000ULL, > > 0x0000000000000000ULL, 0x0000000000000000ULL }; > +attribute_mcmodel_small > DECLARE_ALIGNED(32, const ymm_reg, ff_pb_1) = { > 0x0101010101010101ULL, 0x0101010101010101ULL, > > 0x0101010101010101ULL, 0x0101010101010101ULL }; > DECLARE_ALIGNED(32, const ymm_reg, ff_pb_2) = { > 0x0202020202020202ULL, 0x0202020202020202ULL, > > 0x0202020202020202ULL, 0x0202020202020202ULL }; > +attribute_mcmodel_small > DECLARE_ALIGNED(32, const ymm_reg, ff_pb_3) = { > 0x0303030303030303ULL, 0x0303030303030303ULL, > > 0x0303030303030303ULL, 0x0303030303030303ULL }; > DECLARE_ALIGNED(32, const xmm_reg, ff_pb_15) = { > 0x0F0F0F0F0F0F0F0FULL, 0x0F0F0F0F0F0F0F0FULL }; > +attribute_mcmodel_small > DECLARE_ALIGNED(32, const ymm_reg, ff_pb_80) = { > 0x8080808080808080ULL, 0x8080808080808080ULL, > > 0x8080808080808080ULL, 0x8080808080808080ULL }; > DECLARE_ALIGNED(32, const ymm_reg, ff_pb_FE) = { > 0xFEFEFEFEFEFEFEFEULL, 0xFEFEFEFEFEFEFEFEULL, > diff --git a/libavutil/attributes_internal.h > b/libavutil/attributes_internal.h > index 3df1ee6af3..0c40e6461f 100644 > --- a/libavutil/attributes_internal.h > +++ b/libavutil/attributes_internal.h > @@ -31,4 +31,19 @@ > # define FF_VISIBILITY_POP_HIDDEN > #endif > > +/** > + * Some globals defined in C files are used from hardcoded asm that > assumes small > + * code model (that is, accessing these globals without GOT). This is a > problem > + * when FFMpeg is built with medium code model (-mcmodel=medium) which > allocates > + * all globals in a data section that's unreachable with PC relative > instructions > + * (small code model instruction sequence). We mark all such globals with > this > + * attribute_mcmodel_small to ensure assembly accessible globals continue > to be > + * allocated in sections reachable from PC relative instructions. > + */ > +#if ARCH_X86_64 && defined(__ELF__) && __has_attribute(model) > +# define attribute_mcmodel_small __attribute__(model("small")) > +#else > +# define attribute_mcmodel_small > +#endif > + > #endif /* AVUTIL_ATTRIBUTES_INTERNAL_H */ > -- > 2.48.1.658.g4767266eb4-goog > > _______________________________________________ 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".
