Module: libav
Branch: master
Commit: 3cba1ad76d362c994fa98fb686e04e20826fb579
Author: Henrik Gramner <hen...@gramner.com>
Committer: Anton Khirnov <an...@khirnov.net>
Date: Sun Dec 25 20:24:59 2016 +0100
x86inc: Avoid using eax/rax for storing the stack pointer
When allocating stack space with an alignment requirement that is larger
than the current stack alignment we need to store a copy of the original
stack pointer in order to be able to restore it later.
If we chose to use another register for this purpose we should not pick
eax/rax since it can be overwritten as a return value.
Signed-off-by: Anton Khirnov <an...@khirnov.net>
---
libavutil/x86/x86inc.asm | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/libavutil/x86/x86inc.asm b/libavutil/x86/x86inc.asm
index dca1f78..7941af3 100644
--- a/libavutil/x86/x86inc.asm
+++ b/libavutil/x86/x86inc.asm
@@ -385,7 +385,14 @@ DECLARE_REG_TMP_SIZE 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14
%ifnum %1
%if %1 != 0 && required_stack_alignment > STACK_ALIGNMENT
%if %1 > 0
+ ; Reserve an additional register for storing the original
stack pointer, but avoid using
+ ; eax/rax for this purpose since it can potentially get
overwritten as a return value.
%assign regs_used (regs_used + 1)
+ %if ARCH_X86_64 && regs_used == 7
+ %assign regs_used 8
+ %elif ARCH_X86_64 == 0 && regs_used == 1
+ %assign regs_used 2
+ %endif
%endif
%if ARCH_X86_64 && regs_used < 5 + UNIX64 * 3
; Ensure that we don't clobber any registers containing
arguments. For UNIX64 we also preserve r6 (rax)
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