Patch version 6: - Added support for all `cextern` symbols. - Added attribute_mcmodel_small attribute to other DECLARE_ASM* macros. - Used DECLARE_ASM* macros for symbols that are being accessed from assembly but still marked with non-ASM DECLARE macros.
On Tue, May 6, 2025 at 4:25 PM 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, hardcoded assembly (external asm files, as well as inline > assembly) 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 > --- > libavcodec/ac3dsp.h | 4 +- > libavcodec/cabac.h | 4 +- > libavcodec/h263dsp.h | 3 +- > libavcodec/sbrdsp.h | 3 +- > libavcodec/x86/constants.c | 4 +- > libavcodec/x86/constants.h | 79 +++++++++++++++++---------------- > libavutil/attributes.h | 6 +++ > libavutil/attributes_internal.h | 16 +++++++ > libavutil/mem_internal.h | 16 ++++--- > 9 files changed, 84 insertions(+), 51 deletions(-) > > diff --git a/libavcodec/ac3dsp.h b/libavcodec/ac3dsp.h > index b1b2bced8f..914824025f 100644 > --- a/libavcodec/ac3dsp.h > +++ b/libavcodec/ac3dsp.h > @@ -25,11 +25,13 @@ > #include <stddef.h> > #include <stdint.h> > > +#include "libavutil/mem_internal.h" > + > /** > * Number of mantissa bits written for each bap value. > * bap values with fractional bits are set to 0 and are calculated > separately. > */ > -extern const uint16_t ff_ac3_bap_bits[16]; > +EXTERN_ASM_VAR(const uint16_t, ff_ac3_bap_bits)[16]; > > typedef struct AC3DSPContext { > /** > diff --git a/libavcodec/cabac.h b/libavcodec/cabac.h > index 38d06b2842..70730e4059 100644 > --- a/libavcodec/cabac.h > +++ b/libavcodec/cabac.h > @@ -29,7 +29,9 @@ > > #include <stdint.h> > > -extern const uint8_t ff_h264_cabac_tables[512 + 4*2*64 + 4*64 + 63]; > +#include "libavutil/mem_internal.h" > + > +EXTERN_ASM_VAR(const uint8_t, ff_h264_cabac_tables)[512 + 4*2*64 + 4*64 + > 63]; > #define H264_NORM_SHIFT_OFFSET 0 > #define H264_LPS_RANGE_OFFSET 512 > #define H264_MLPS_STATE_OFFSET 1024 > diff --git a/libavcodec/h263dsp.h b/libavcodec/h263dsp.h > index 2dccd23392..fd107e7546 100644 > --- a/libavcodec/h263dsp.h > +++ b/libavcodec/h263dsp.h > @@ -20,8 +20,9 @@ > #define AVCODEC_H263DSP_H > > #include <stdint.h> > +#include "libavutil/mem_internal.h" > > -extern const uint8_t ff_h263_loop_filter_strength[32]; > +EXTERN_ASM_VAR(const uint8_t, ff_h263_loop_filter_strength)[32]; > > typedef struct H263DSPContext { > void (*h263_h_loop_filter)(uint8_t *src, int stride, int qscale); > diff --git a/libavcodec/sbrdsp.h b/libavcodec/sbrdsp.h > index 09b2cbfc10..8ce467c0fb 100644 > --- a/libavcodec/sbrdsp.h > +++ b/libavcodec/sbrdsp.h > @@ -23,6 +23,7 @@ > > #include <stdint.h> > #include "aac_defines.h" > +#include "libavutil/mem_internal.h" > > typedef struct SBRDSPContext { > void (*sum64x5)(INTFLOAT *z); > @@ -43,7 +44,7 @@ typedef struct SBRDSPContext { > int kx, int m_max); > } SBRDSPContext; > > -extern const INTFLOAT AAC_RENAME(ff_sbr_noise_table)[][2]; > +EXTERN_ASM_VAR(const INTFLOAT, AAC_RENAME(ff_sbr_noise_table))[][2]; > > void AAC_RENAME(ff_sbrdsp_init)(SBRDSPContext *s); > void ff_sbrdsp_init_arm(SBRDSPContext *s); > diff --git a/libavcodec/x86/constants.c b/libavcodec/x86/constants.c > index c5f3c6428e..ed0d456d99 100644 > --- a/libavcodec/x86/constants.c > +++ b/libavcodec/x86/constants.c > @@ -46,7 +46,7 @@ DECLARE_ALIGNED(32, const ymm_reg, ff_pw_256) = { > 0x0100010001000100ULL, 0x010 > > 0x0100010001000100ULL, 0x0100010001000100ULL }; > DECLARE_ALIGNED(32, const ymm_reg, ff_pw_512) = { > 0x0200020002000200ULL, 0x0200020002000200ULL, > > 0x0200020002000200ULL, 0x0200020002000200ULL }; > -DECLARE_ALIGNED(16, const xmm_reg, ff_pw_1019) = { > 0x03FB03FB03FB03FBULL, 0x03FB03FB03FB03FBULL }; > +DECLARE_ASM_ALIGNED(16, const xmm_reg, ff_pw_1019) = { > 0x03FB03FB03FB03FBULL, 0x03FB03FB03FB03FBULL }; > DECLARE_ALIGNED(32, const ymm_reg, ff_pw_1023) = { > 0x03ff03ff03ff03ffULL, 0x03ff03ff03ff03ffULL, > > 0x03ff03ff03ff03ffULL, 0x03ff03ff03ff03ffULL}; > DECLARE_ALIGNED(32, const ymm_reg, ff_pw_1024) = { > 0x0400040004000400ULL, 0x0400040004000400ULL, > @@ -70,7 +70,7 @@ DECLARE_ALIGNED(32, const ymm_reg, ff_pb_2) = { > 0x0202020202020202ULL, 0x020 > > 0x0202020202020202ULL, 0x0202020202020202ULL }; > DECLARE_ALIGNED(32, const ymm_reg, ff_pb_3) = { > 0x0303030303030303ULL, 0x0303030303030303ULL, > > 0x0303030303030303ULL, 0x0303030303030303ULL }; > -DECLARE_ALIGNED(32, const xmm_reg, ff_pb_15) = { > 0x0F0F0F0F0F0F0F0FULL, 0x0F0F0F0F0F0F0F0FULL }; > +DECLARE_ASM_ALIGNED(32, const xmm_reg, ff_pb_15) = { > 0x0F0F0F0F0F0F0F0FULL, 0x0F0F0F0F0F0F0F0FULL }; > 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/libavcodec/x86/constants.h b/libavcodec/x86/constants.h > index 4a55adb5b3..c2e0fd8f02 100644 > --- a/libavcodec/x86/constants.h > +++ b/libavcodec/x86/constants.h > @@ -23,49 +23,50 @@ > > #include <stdint.h> > > +#include "libavutil/mem_internal.h" > #include "libavutil/x86/asm.h" > > -extern const ymm_reg ff_pw_1; > -extern const ymm_reg ff_pw_2; > -extern const xmm_reg ff_pw_3; > -extern const ymm_reg ff_pw_4; > -extern const xmm_reg ff_pw_5; > -extern const xmm_reg ff_pw_8; > -extern const xmm_reg ff_pw_9; > -extern const uint64_t ff_pw_15; > -extern const xmm_reg ff_pw_16; > -extern const xmm_reg ff_pw_18; > -extern const xmm_reg ff_pw_20; > -extern const xmm_reg ff_pw_32; > -extern const uint64_t ff_pw_53; > -extern const xmm_reg ff_pw_64; > -extern const uint64_t ff_pw_128; > -extern const ymm_reg ff_pw_255; > -extern const ymm_reg ff_pw_256; > -extern const ymm_reg ff_pw_512; > -extern const ymm_reg ff_pw_1023; > -extern const ymm_reg ff_pw_1024; > -extern const ymm_reg ff_pw_2048; > -extern const ymm_reg ff_pw_4095; > -extern const ymm_reg ff_pw_4096; > -extern const ymm_reg ff_pw_8192; > -extern const ymm_reg ff_pw_m1; > +EXTERN_ASM_VAR(const ymm_reg, ff_pw_1); > +EXTERN_ASM_VAR(const ymm_reg, ff_pw_2); > +EXTERN_ASM_VAR(const xmm_reg, ff_pw_3); > +EXTERN_ASM_VAR(const ymm_reg, ff_pw_4); > +EXTERN_ASM_VAR(const xmm_reg, ff_pw_5); > +EXTERN_ASM_VAR(const xmm_reg, ff_pw_8); > +EXTERN_ASM_VAR(const xmm_reg, ff_pw_9); > +EXTERN_ASM_VAR(const uint64_t, ff_pw_15); > +EXTERN_ASM_VAR(const xmm_reg, ff_pw_16); > +EXTERN_ASM_VAR(const xmm_reg, ff_pw_18); > +EXTERN_ASM_VAR(const xmm_reg, ff_pw_20); > +EXTERN_ASM_VAR(const xmm_reg, ff_pw_32); > +EXTERN_ASM_VAR(const uint64_t, ff_pw_53); > +EXTERN_ASM_VAR(const xmm_reg, ff_pw_64); > +EXTERN_ASM_VAR(const uint64_t, ff_pw_128); > +EXTERN_ASM_VAR(const ymm_reg, ff_pw_255); > +EXTERN_ASM_VAR(const ymm_reg, ff_pw_256); > +EXTERN_ASM_VAR(const ymm_reg, ff_pw_512); > +EXTERN_ASM_VAR(const ymm_reg, ff_pw_1023); > +EXTERN_ASM_VAR(const ymm_reg, ff_pw_1024); > +EXTERN_ASM_VAR(const ymm_reg, ff_pw_2048); > +EXTERN_ASM_VAR(const ymm_reg, ff_pw_4095); > +EXTERN_ASM_VAR(const ymm_reg, ff_pw_4096); > +EXTERN_ASM_VAR(const ymm_reg, ff_pw_8192); > +EXTERN_ASM_VAR(const ymm_reg, ff_pw_m1); > > -extern const ymm_reg ff_pb_0; > -extern const ymm_reg ff_pb_1; > -extern const ymm_reg ff_pb_2; > -extern const ymm_reg ff_pb_3; > -extern const ymm_reg ff_pb_80; > -extern const ymm_reg ff_pb_FE; > -extern const uint64_t ff_pb_FC; > +EXTERN_ASM_VAR(const ymm_reg, ff_pb_0); > +EXTERN_ASM_VAR(const ymm_reg, ff_pb_1); > +EXTERN_ASM_VAR(const ymm_reg, ff_pb_2); > +EXTERN_ASM_VAR(const ymm_reg, ff_pb_3); > +EXTERN_ASM_VAR(const ymm_reg, ff_pb_80); > +EXTERN_ASM_VAR(const ymm_reg, ff_pb_FE); > +EXTERN_ASM_VAR(const uint64_t, ff_pb_FC); > > -extern const xmm_reg ff_ps_neg; > +EXTERN_ASM_VAR(const xmm_reg, ff_ps_neg); > > -extern const ymm_reg ff_pd_1; > -extern const ymm_reg ff_pd_16; > -extern const ymm_reg ff_pd_32; > -extern const ymm_reg ff_pd_64; > -extern const ymm_reg ff_pd_8192; > -extern const ymm_reg ff_pd_65535; > +EXTERN_ASM_VAR(const ymm_reg, ff_pd_1); > +EXTERN_ASM_VAR(const ymm_reg, ff_pd_16); > +EXTERN_ASM_VAR(const ymm_reg, ff_pd_32); > +EXTERN_ASM_VAR(const ymm_reg, ff_pd_64); > +EXTERN_ASM_VAR(const ymm_reg, ff_pd_8192); > +EXTERN_ASM_VAR(const ymm_reg, ff_pd_65535); > > #endif /* AVCODEC_X86_CONSTANTS_H */ > diff --git a/libavutil/attributes.h b/libavutil/attributes.h > index 04c615c952..dfc35fa31e 100644 > --- a/libavutil/attributes.h > +++ b/libavutil/attributes.h > @@ -40,6 +40,12 @@ > # define AV_HAS_BUILTIN(x) 0 > #endif > > +#ifdef __has_attribute > +# define AV_HAS_ATTRIBUTE(x) __has_attribute(x) > +#else > +# define AV_HAS_ATTRIBUTE(x) 0 > +#endif > + > #ifndef av_always_inline > #if AV_GCC_VERSION_AT_LEAST(3,1) > # define av_always_inline __attribute__((always_inline)) inline > diff --git a/libavutil/attributes_internal.h > b/libavutil/attributes_internal.h > index bc85ce77ff..c557fa0af0 100644 > --- a/libavutil/attributes_internal.h > +++ b/libavutil/attributes_internal.h > @@ -19,6 +19,7 @@ > #ifndef AVUTIL_ATTRIBUTES_INTERNAL_H > #define AVUTIL_ATTRIBUTES_INTERNAL_H > > +#include "config.h" > #include "attributes.h" > > #if (AV_GCC_VERSION_AT_LEAST(4,0) || defined(__clang__)) && > (defined(__ELF__) || defined(__MACH__)) > @@ -33,4 +34,19 @@ > > #define EXTERN extern attribute_visibility_hidden > > +/** > + * 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__) && AV_HAS_ATTRIBUTE(model) > +# define attribute_mcmodel_small __attribute__((model("small"))) > +#else > +# define attribute_mcmodel_small > +#endif > + > #endif /* AVUTIL_ATTRIBUTES_INTERNAL_H */ > diff --git a/libavutil/mem_internal.h b/libavutil/mem_internal.h > index c027fa51c3..c621fa861f 100644 > --- a/libavutil/mem_internal.h > +++ b/libavutil/mem_internal.h > @@ -29,6 +29,7 @@ > #endif > > #include "attributes.h" > +#include "attributes_internal.h" > #include "macros.h" > > /** > @@ -78,16 +79,19 @@ > > #if defined(__DJGPP__) > #define DECLARE_ALIGNED_T(n,t,v) alignas(FFMIN(n, 16)) t v > - #define DECLARE_ASM_ALIGNED(n,t,v) alignas(FFMIN(n, 16)) t av_used v > - #define DECLARE_ASM_CONST(n,t,v) alignas(FFMIN(n, 16)) static > const t av_used v > + #define DECLARE_ASM_ALIGNED(n,t,v) alignas(FFMIN(n, 16)) t av_used > attribute_mcmodel_small v > + #define DECLARE_ASM_CONST(n,t,v) alignas(FFMIN(n, 16)) static > const t av_used attribute_mcmodel_small v > + #define EXTERN_ASM_VAR(t,v) extern t attribute_mcmodel_small v > #elif defined(_MSC_VER) > #define DECLARE_ALIGNED_T(n,t,v) __declspec(align(n)) t v > - #define DECLARE_ASM_ALIGNED(n,t,v) __declspec(align(n)) t v > - #define DECLARE_ASM_CONST(n,t,v) __declspec(align(n)) static const > t v > + #define DECLARE_ASM_ALIGNED(n,t,v) __declspec(align(n)) t > attribute_mcmodel_small v > + #define DECLARE_ASM_CONST(n,t,v) __declspec(align(n)) static const > t attribute_mcmodel_small v > + #define EXTERN_ASM_VAR(t,v) extern t attribute_mcmodel_small v > #else > #define DECLARE_ALIGNED_T(n,t,v) alignas(n) t v > - #define DECLARE_ASM_ALIGNED(n,t,v) alignas(n) t av_used v > - #define DECLARE_ASM_CONST(n,t,v) alignas(n) static const t av_used > v > + #define DECLARE_ASM_ALIGNED(n,t,v) alignas(n) t av_used > attribute_mcmodel_small v > + #define DECLARE_ASM_CONST(n,t,v) alignas(n) static const t av_used > attribute_mcmodel_small v > + #define EXTERN_ASM_VAR(t,v) extern t attribute_mcmodel_small v > #endif > > #if HAVE_SIMD_ALIGN_64 > -- > 2.49.0.987.g0cc8ee98dc-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".
