c3-lang/libffi

2020-10-27T07:02:36

Removing unnecessary instruction from ffi_call_unix64 (#588) unix64.S's `ffi_call_unix64` looks like it used to take six parameters, where the sixth said the number of SSE register arguments. However, currently the function only takes five parameters, and the number of SSE register arguments is encoded in the `struct register_args *` passed as the first parameter to `ffi_call_unix64`. This change removes an instruction that tries to use this missing sixth parameter as the number of SSE arguments. This fix should not change any behavior, nor fix any bugs, because a few instructions later the value moved from %r9d into %eax is overwritten by the correct value anyway. This change merely makes the code a tad less confusing, because currently the assembly moves from a register (r9) whose value is never set.

diff --git a/src/x86/unix64.S b/src/x86/unix64.S
index ee3c04f..89d7db1 100644
--- a/src/x86/unix64.S
+++ b/src/x86/unix64.S
@@ -84,7 +84,6 @@ L(UW1):
 
 	movq	%rdi, %r10		/* Save a copy of the register area. */
 	movq	%r8, %r11		/* Save a copy of the target fn.  */
-	movl	%r9d, %eax		/* Set number of SSE registers.  */
 
 	/* Load up all argument registers.  */
 	movq	(%r10), %rdi
@@ -93,7 +92,7 @@ L(UW1):
 	movq	0x18(%r10), %rcx
 	movq	0x20(%r10), %r8
 	movq	0x28(%r10), %r9
-	movl	0xb0(%r10), %eax
+	movl	0xb0(%r10), %eax	/* Set number of SSE registers.  */
 	testl	%eax, %eax
 	jnz	L(load_sse)
 L(ret_from_load_sse):