Re: [FFmpeg-devel] [PATCH 2/2] libavcodec: Set hidden visibility on global symbols accessed from x86_64 assembly

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Thomas Guillem:
> DECLARE_ALIGNED, DECLARE_ASM_ALIGNED, and DECLARE_ASM_CONST will include
> attribute_visibility_hidden.
> 
> ld: error: relocation R_X86_64_PC32 cannot be used against symbol 'ff_h264_cabac_tables'; recompile with -fPIC
>>>> defined in /home/tom/work/git/vlc-android/vlc/contrib/x86_64-linux-android/lib/libavcodec.a(cabac.o)
>>>> referenced by cabac.h:187 (libavcodec/x86/cabac.h:187)
>>>>               h264_cabac.o:(ff_h264_decode_mb_cabac) in archive /home/tom/work/git/vlc-android/vlc/contrib/x86_64-linux-android/lib/libavcodec.a
> ---
>  libavcodec/ac3dsp.h        |  3 +-
>  libavcodec/cabac.h         |  3 +-
>  libavcodec/h263dsp.h       |  3 +-
>  libavcodec/x86/constants.h | 81 +++++++++++++++++++-------------------
>  libavutil/mem.h            |  6 +--
>  libswscale/x86/rgb2rgb.c   |  2 +-
>  6 files changed, 51 insertions(+), 47 deletions(-)
> 
> diff --git a/libavcodec/ac3dsp.h b/libavcodec/ac3dsp.h
> index a23b11526e..f8c03a7c23 100644
> --- a/libavcodec/ac3dsp.h
> +++ b/libavcodec/ac3dsp.h
> @@ -23,12 +23,13 @@
>  #define AVCODEC_AC3DSP_H
>  
>  #include <stdint.h>
> +#include "libavutil/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 const uint16_t attribute_visibility_hidden ff_ac3_bap_bits[16];
>  
>  typedef struct AC3DSPContext {
>      /**
> diff --git a/libavcodec/cabac.h b/libavcodec/cabac.h
> index 38d06b2842..356aa368d0 100644
> --- a/libavcodec/cabac.h
> +++ b/libavcodec/cabac.h
> @@ -28,8 +28,9 @@
>  #define AVCODEC_CABAC_H
>  
>  #include <stdint.h>
> +#include "libavutil/internal.h"
>  
> -extern const uint8_t ff_h264_cabac_tables[512 + 4*2*64 + 4*64 + 63];
> +extern const uint8_t attribute_visibility_hidden 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 1abea3ca8c..514a148fb1 100644
> --- a/libavcodec/h263dsp.h
> +++ b/libavcodec/h263dsp.h
> @@ -20,8 +20,9 @@
>  #define AVCODEC_H263DSP_H
>  
>  #include <stdint.h>
> +#include "libavutil/internal.h"
>  
> -extern const uint8_t ff_h263_loop_filter_strength[32];
> +extern const uint8_t attribute_visibility_hidden 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/x86/constants.h b/libavcodec/x86/constants.h
> index 85da38b7b9..c84b0d4324 100644
> --- a/libavcodec/x86/constants.h
> +++ b/libavcodec/x86/constants.h
> @@ -22,51 +22,52 @@
>  #define AVCODEC_X86_CONSTANTS_H
>  
>  #include <stdint.h>
> +#include "libavutil/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_42;
> -extern const uint64_t ff_pw_53;
> -extern const xmm_reg  ff_pw_64;
> -extern const uint64_t ff_pw_96;
> -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 const ymm_reg attribute_visibility_hidden  ff_pw_1;
> +extern const ymm_reg attribute_visibility_hidden  ff_pw_2;
> +extern const xmm_reg attribute_visibility_hidden  ff_pw_3;
> +extern const ymm_reg attribute_visibility_hidden  ff_pw_4;
> +extern const xmm_reg attribute_visibility_hidden  ff_pw_5;
> +extern const xmm_reg attribute_visibility_hidden  ff_pw_8;
> +extern const xmm_reg attribute_visibility_hidden  ff_pw_9;
> +extern const uint64_t attribute_visibility_hidden ff_pw_15;
> +extern const xmm_reg attribute_visibility_hidden  ff_pw_16;
> +extern const xmm_reg attribute_visibility_hidden  ff_pw_18;
> +extern const xmm_reg attribute_visibility_hidden  ff_pw_20;
> +extern const xmm_reg attribute_visibility_hidden  ff_pw_32;
> +extern const uint64_t attribute_visibility_hidden ff_pw_42;
> +extern const uint64_t attribute_visibility_hidden ff_pw_53;
> +extern const xmm_reg attribute_visibility_hidden  ff_pw_64;
> +extern const uint64_t attribute_visibility_hidden ff_pw_96;
> +extern const uint64_t attribute_visibility_hidden ff_pw_128;
> +extern const ymm_reg attribute_visibility_hidden  ff_pw_255;
> +extern const ymm_reg attribute_visibility_hidden  ff_pw_256;
> +extern const ymm_reg attribute_visibility_hidden  ff_pw_512;
> +extern const ymm_reg attribute_visibility_hidden  ff_pw_1023;
> +extern const ymm_reg attribute_visibility_hidden  ff_pw_1024;
> +extern const ymm_reg attribute_visibility_hidden  ff_pw_2048;
> +extern const ymm_reg attribute_visibility_hidden  ff_pw_4095;
> +extern const ymm_reg attribute_visibility_hidden  ff_pw_4096;
> +extern const ymm_reg attribute_visibility_hidden  ff_pw_8192;
> +extern const ymm_reg attribute_visibility_hidden  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 const ymm_reg attribute_visibility_hidden  ff_pb_0;
> +extern const ymm_reg attribute_visibility_hidden  ff_pb_1;
> +extern const ymm_reg attribute_visibility_hidden  ff_pb_2;
> +extern const ymm_reg attribute_visibility_hidden  ff_pb_3;
> +extern const ymm_reg attribute_visibility_hidden  ff_pb_80;
> +extern const ymm_reg attribute_visibility_hidden  ff_pb_FE;
> +extern const uint64_t attribute_visibility_hidden ff_pb_FC;
>  
> -extern const xmm_reg  ff_ps_neg;
> +extern const xmm_reg attribute_visibility_hidden  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_8192;
> -extern const ymm_reg  ff_pd_65535;
> +extern const ymm_reg attribute_visibility_hidden  ff_pd_1;
> +extern const ymm_reg attribute_visibility_hidden  ff_pd_16;
> +extern const ymm_reg attribute_visibility_hidden  ff_pd_32;
> +extern const ymm_reg attribute_visibility_hidden  ff_pd_8192;
> +extern const ymm_reg attribute_visibility_hidden  ff_pd_65535;
>  

This is total overkill; the visibility pragma exists for a reason.

>  #endif /* AVCODEC_X86_CONSTANTS_H */
> diff --git a/libavutil/mem.h b/libavutil/mem.h
> index d91174196c..88fea4bfe7 100644
> --- a/libavutil/mem.h
> +++ b/libavutil/mem.h
> @@ -113,9 +113,9 @@
>      #define DECLARE_ASM_ALIGNED(n,t,v)  t av_used __attribute__ ((aligned (FFMIN(n, 16)))) v
>      #define DECLARE_ASM_CONST(n,t,v)    static const t av_used __attribute__ ((aligned (FFMIN(n, 16)))) v
>  #elif defined(__GNUC__) || defined(__clang__)
> -    #define DECLARE_ALIGNED(n,t,v)      t __attribute__ ((aligned (n))) v
> -    #define DECLARE_ASM_ALIGNED(n,t,v)  t av_used __attribute__ ((aligned (n))) v
> -    #define DECLARE_ASM_CONST(n,t,v)    static const t av_used __attribute__ ((aligned (n))) v
> +    #define DECLARE_ALIGNED(n,t,v)      attribute_visibility_hidden t __attribute__ ((aligned (n))) v
> +    #define DECLARE_ASM_ALIGNED(n,t,v)  attribute_visibility_hidden t av_used __attribute__ ((aligned (n))) v
> +    #define DECLARE_ASM_CONST(n,t,v)    attribute_visibility_hidden static const t av_used __attribute__ ((aligned (n))) v

You can't simply change the semantics of public defines; furthermore,
attribute_visibility_hidden should not be public. If these macros are to
be changed, then you need to modify mem.h to only define them in case
HAVE_AV_CONFIG_H is not defined (HAVE_AV_CONFIG_H is defined when
building our libraries). Then the macros from mem_internal.h will be
used and these can be modified.
(Furthermore, adding the attribute to DECLARE_ASM_CONST is pointless, as
it is already static.)

>  #elif defined(_MSC_VER)
>      #define DECLARE_ALIGNED(n,t,v)      __declspec(align(n)) t v
>      #define DECLARE_ASM_ALIGNED(n,t,v)  __declspec(align(n)) t v
> diff --git a/libswscale/x86/rgb2rgb.c b/libswscale/x86/rgb2rgb.c
> index b325e5dbd5..100f608d04 100644
> --- a/libswscale/x86/rgb2rgb.c
> +++ b/libswscale/x86/rgb2rgb.c
> @@ -70,7 +70,7 @@ DECLARE_ASM_CONST(8, uint64_t, mul15_hi)     = 0x0210021002100210ULL;
>  DECLARE_ASM_CONST(8, uint64_t, mul16_mid)    = 0x2080208020802080ULL;
>  
>  DECLARE_ALIGNED(8, extern const uint64_t, ff_bgr2YOffset);
> -DECLARE_ALIGNED(8, extern const uint64_t, ff_w1111);
> +attribute_visibility_hidden DECLARE_ALIGNED(8, extern const uint64_t, ff_w1111);
>  DECLARE_ALIGNED(8, extern const uint64_t, ff_bgr2UVOffset);
>  
>  #define BY ((int)( 0.098*(1<<RGB2YUV_SHIFT)+0.5))

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