[FFmpeg-devel] [PATCH 2/2] checkasm: x86: properly save rdx/edx in checked_call()

Henrik Gramner henrik at gramner.com
Sun Aug 16 18:40:57 CEST 2015

If the return value doesn't fit in a single register rdx/edx can in some
cases be used in addition to rax/eax.

Doesn't affect any of the existing checkasm tests but might be useful later.

Also comment the relevant code a bit better.
 tests/checkasm/x86/checkasm.asm | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/tests/checkasm/x86/checkasm.asm b/tests/checkasm/x86/checkasm.asm
index 377fd37..da19aa2 100644
--- a/tests/checkasm/x86/checkasm.asm
+++ b/tests/checkasm/x86/checkasm.asm
@@ -145,10 +145,15 @@ cglobal checked_call, 2,15,16,max_args*8+8
     or  r14, r5
+    ; Call fail_func() with a descriptive message to mark it as a failure
+    ; if the called function didn't preserve all callee-saved registers.
+    ; Save the return value located in rdx:rax first to prevent clobbering.
     jz .ok
     mov  r9, rax
+    mov r10, rdx
     lea  r0, [error_message]
     call fail_func
+    mov rdx, r10
     mov rax, r9
@@ -182,9 +187,11 @@ cglobal checked_call, 1,7
     or   r3, r5
     jz .ok
     mov  r3, eax
+    mov  r4, edx
     lea  r0, [error_message]
     mov [esp], r0
     call fail_func
+    mov  edx, r4
     mov  eax, r3
     add  esp, max_args*4

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