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[FFmpeg-devel] avutil/mem: Mark DECLARE_ASM_ALIGNED as visibility("hidden") for __GNUC__

Message ID CAFP8O3JdKU0adFXBgJjxP=Dg+PEDeEy7+0LQYE7Mks0VbADQhA@mail.gmail.com
State Superseded
Headers show

Commit Message

Fangrui Song March 7, 2019, 3:36 a.m. UTC 
On Wed, Mar 6, 2019 at 4:14 PM Carl Eugen Hoyos <ceffmpeg@gmail.com> wrote:

> 2019-02-21 2:37 GMT+01:00, Fāng-ruì Sòng <maskray-at-google.com@ffmpeg.org
> >:
> > Sorry if this doesn't attach to the correct thread as I didn't
> > subscribe to this list and don't know the Message-ID of the thread.
>
> The thread works fine here with gmail but your patch was corrupted,
> you have to attach it.
>
> Carl Eugen
>
>
Sorry. Here is the attached patch (git format-patch -1 --stdout).
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Patch

From 63d1c46c9796ca4a804cc89573c8f4613716b50d Mon Sep 17 00:00:00 2001
From: Fangrui Song <maskray@google.com>
Date: Wed, 20 Feb 2019 16:25:46 +0800
Subject: [PATCH] avutil/mem: Mark DECLARE_ASM_ALIGNED as visibility("hidden")
 for __GNUC__

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, when -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. 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.

Signed-off-by: Fangrui Song <i@maskray.me>
---
 libavutil/mem.h | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/libavutil/mem.h b/libavutil/mem.h
index 5fb1a02..9afeed0 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
@@ -110,7 +116,7 @@ 
     #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_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
-- 
2.20.1