| Message ID | CAFP8O3LXFVbGwk+=P-MhG9cs5bJHZhhzhfNpJi52uErFQ5d8aQ@mail.gmail.com |
|---|---|
| State | Superseded |
| Headers | show |
2019-02-20 10:13 GMT+01:00, Fāng-ruì Sòng <maskray-at-google.com@ffmpeg.org>: > Inline asm code assumes these DECLARE_ASM_ALIGNED declared global > constants are non-preemptive, e.g. > > libavcodec/x86/cabac.h > "lea "MANGLE(ff_h264_cabac_tables)", %0 \n\t" > > On ELF platforms, if -Wl,-Bsymbolic > -Wl,--version-script,libavcodec/libavcodec.ver are removed from the > linker command line, the symbol will be considered preemptive and fail Why is it a good idea to remove them from the linker command line? > to link to a DSO: > > ld.lld: error: relocation R_X86_64_PC32 cannot be used against > symbol ff_h264_cabac_tables; recompile with -fPIC > > It is better to express the intention explicitly and mark such global > constants hidden (non-preemptive). It also improves portability as no > linker magic is required. > > DECLARE_ASM_CONST uses the "static" specifier to indicate internal > linkage. The visibility annotation is unnecessary. > > Also remove __clang__ as clang pretends to be gcc 4.2 and defines __GNUC__ The word "also" indicates here that this should be an independent patch. Carl Eugen
On Wed, Feb 20, 2019 at 8:03 PM Fāng-ruì Sòng <maskray-at-google.com@ffmpeg.org> wrote: > --- a/libavutil/mem.h > +++ b/libavutil/mem.h > > +#if defined(__GNUC__) && !(defined(_WIN32) || defined(__CYGWIN__)) > + #define DECLARE_HIDDEN __attribute__ ((visibility ("hidden"))) > +#else > + #define DECLARE_HIDDEN > +#endif libavutil/mem.h is a public header so any defines added should have appropriate prefixes (yes, the existing defines violate this which is something that should be addressed, but that's a different issue). Alternatively maybe those macros should be moved to some internal header because I don't really see any value of having inline asm support macros public.
On Thu, Mar 14, 2019 at 9:59 AM Henrik Gramner <henrik@gramner.com> wrote: > > On Wed, Feb 20, 2019 at 8:03 PM Fāng-ruì Sòng > <maskray-at-google.com@ffmpeg.org> wrote: > > --- a/libavutil/mem.h > > +++ b/libavutil/mem.h > > > > +#if defined(__GNUC__) && !(defined(_WIN32) || defined(__CYGWIN__)) > > + #define DECLARE_HIDDEN __attribute__ ((visibility ("hidden"))) > > +#else > > + #define DECLARE_HIDDEN > > +#endif > > libavutil/mem.h is a public header so any defines added should have > appropriate prefixes (yes, the existing defines violate this which is > something that should be addressed, but that's a different issue). Do you have suggestions on the naming? av_declare_hidden? > Alternatively maybe those macros should be moved to some internal > header because I don't really see any value of having inline asm > support macros public. That would change too many files. I'd rather not do that in this patch.
diff --git a/libavutil/mem.h b/libavutil/mem.h index 5fb1a02dd9..47abe2c8e9 100644 --- a/libavutil/mem.h +++ b/libavutil/mem.h @@ -100,6 +100,12 @@ * @param v Name of the variable */ +#if defined(__GNUC__) && !(defined(_WIN32) || defined(__CYGWIN__)) + #define DECLARE_HIDDEN __attribute__ ((visibility ("hidden"))) +#else + #define DECLARE_HIDDEN +#endif + #if defined(__INTEL_COMPILER) && __INTEL_COMPILER < 1110 || defined(__SUNPRO_C) #define DECLARE_ALIGNED(n,t,v) t __attribute__ ((aligned (n))) v #define DECLARE_ASM_ALIGNED(n,t,v) t __attribute__ ((aligned (n))) v @@ -108,9 +114,9 @@ #define DECLARE_ALIGNED(n,t,v) t __attribute__ ((aligned (FFMIN(n, 16)))) v #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__) +#elif defined(__GNUC__) #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
Inline asm code assumes these DECLARE_ASM_ALIGNED declared global constants are non-preemptive, e.g. libavcodec/x86/cabac.h "lea "MANGLE(ff_h264_cabac_tables)", %0 \n\t" On ELF platforms, if -Wl,-Bsymbolic -Wl,--version-script,libavcodec/libavcodec.ver are removed from the linker command line, the symbol will be considered preemptive and fail to link to a DSO: ld.lld: error: relocation R_X86_64_PC32 cannot be used against symbol ff_h264_cabac_tables; recompile with -fPIC It is better to express the intention explicitly and mark such global constants hidden (non-preemptive). It also improves portability as no linker magic is required. DECLARE_ASM_CONST uses the "static" specifier to indicate internal linkage. The visibility annotation is unnecessary. Also remove __clang__ as clang pretends to be gcc 4.2 and defines __GNUC__ Signed-off-by: Fangrui Song <maskray@google.com> --- libavutil/mem.h | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) + #define DECLARE_ASM_ALIGNED(n,t,v) t av_used __attribute__ ((aligned (n))) DECLARE_HIDDEN v #define DECLARE_ASM_CONST(n,t,v) static const t av_used __attribute__ ((aligned (n))) v #elif defined(_MSC_VER) #define DECLARE_ALIGNED(n,t,v) __declspec(align(n)) t v