[FFmpeg-cvslog] x86: h264: Don' t keep data in the redzone across function calls on 64 bit unix

Martin Storsjö git at videolan.org
Tue Jun 10 18:48:19 CEST 2014

ffmpeg | branch: master | Martin Storsjö <martin at martin.st> | Mon Feb 20 11:24:35 2012 +0200| [570d4b21863b6254d6bbca9c528bede471bb4478] | committer: Martin Storsjö

x86: h264: Don't keep data in the redzone across function calls on 64 bit unix

We know that the called function (ff_chroma_inter_body_mmxext)
doesn't touch the redzone, and thus will be kept intact - thus,
this doesn't fix any bug per se.

However, valgrind's memcheck tool intentionally assumes that the
redzone is clobbered on every function call and function return
(see a long comment in valgrind/memcheck/mc_main.c). This avoids
false positives in that tool, at the cost of an extra stack pointer

The other alternative would be a valgrind suppression for this issue,
but that's an extra burden for everybody that wants to run libavcodec
within valgrind.

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

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=570d4b21863b6254d6bbca9c528bede471bb4478

 libavcodec/x86/h264_deblock.asm |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/libavcodec/x86/h264_deblock.asm b/libavcodec/x86/h264_deblock.asm
index 8a9fdf6..61642a0 100644
--- a/libavcodec/x86/h264_deblock.asm
+++ b/libavcodec/x86/h264_deblock.asm
@@ -821,10 +821,10 @@ cglobal deblock_v_chroma_8, 5,6
 ;                          int8_t *tc0)
 cglobal deblock_h_chroma_8, 5,7
-%if UNIX64
-    %define buf0 [rsp-24]
-    %define buf1 [rsp-16]
-%elif WIN64
+%if ARCH_X86_64
+    ; This could use the red zone on 64 bit unix to avoid the stack pointer
+    ; readjustment, but valgrind assumes the red zone is clobbered on
+    ; function calls and returns.
     sub   rsp, 16
     %define buf0 [rsp]
     %define buf1 [rsp+8]
@@ -840,7 +840,7 @@ cglobal deblock_h_chroma_8, 5,7
     movq  m0, buf0
     movq  m3, buf1
     TRANSPOSE8x4B_STORE PASS8ROWS(t5, r0, r1, t6)
-%if WIN64
+%if ARCH_X86_64
     add   rsp, 16

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