[FFmpeg-cvslog] avutil: Fix linking x86 asm constants with Clang in MSVC mode

[Martin Storsjö]

ffmpeg | branch: master | Martin Storsjö <martin at martin.st> | Thu Jun 12 12:06:15 2025 +0300| [fb65ecbc9b805571e5ff707b935c343803137e54] | committer: Martin Storsjö

avutil: Fix linking x86 asm constants with Clang in MSVC mode

This fixes building with Clang in MSVC mode, for x86, which was
broken in 6e49b8699657b808b7dc80033f2c3f2d0e029fa3 (in Nov 2024);
previously it failed with undefined symbols for the constants
defined with DECLARE_ASM_CONST, accessed via inline assembly.

Before 57861911a34e1c33796be97f2b2f44e05fffd647, there was an
    #elif defined(__GNUC__) || defined(__clang__)
case before the
    #elif defined(_MSC_VER)
case for defining DECLARE_ASM_CONST, which included av_used.
(This case included the explicit "defined(__clang__)" since
f637046d3134a331e4b5a7243ac3dfb92735b8a5.)

After 57861911a34e1c33796be97f2b2f44e05fffd647, it used the
generic definition of DECLARE_ASM_CONST that also included
av_used - which also worked for Clang in MSVC mode. But after
6e49b8699657b808b7dc80033f2c3f2d0e029fa3, Clang in MSVC mode
ended up using the MSVC specific variant which lacked the
av_used declaration, causing linker errors due to undefined
symbols.

Signed-off-by: Martin Storsjö <martin at martin.st>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=fb65ecbc9b805571e5ff707b935c343803137e54
---

 libavutil/mem_internal.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libavutil/mem_internal.h b/libavutil/mem_internal.h
index d58881d09c..78adc4f407 100644
--- a/libavutil/mem_internal.h
+++ b/libavutil/mem_internal.h
@@ -82,8 +82,8 @@
     #define DECLARE_ASM_CONST(n,t,v)    alignas(FFMIN(n, 16)) static const t av_used 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 av_used v
+    #define DECLARE_ASM_CONST(n,t,v)    __declspec(align(n)) static const t av_used 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