Fixes for w64 ABI.

1 files changed, 10 insertions, 3 deletions

diff --git a/x86_64/README b/x86_64/README
index ae693be5..d04e5dfc 100644
--- a/x86_64/README
+++ b/x86_64/README
@@ -4,6 +4,8 @@ Up to 6 integer and pointer arguments are passed in registers. Nine
 registers, %rax, %rcx, %rdx, %rsi, %rdi and %r8-%r11 can be used
 freely. Integers and pointers are returned in %rax.
 
+At entry, it is required that %rsp == 8 (mod 16).
+
 Registers	May be		Argument
 		clobbered	number
 
@@ -51,14 +53,19 @@ Additional arguments are passed on the stack. "backing store" on the
 stack for the four register arguments is also required. %xmm6 to
 %xmm15 are callee-saved. The "long" type is just 32 bits.
 
-If we have five arguments, and push the additional callee-save
+If we have six arguments, and push the additional callee-save
 registers %rdi and %rsi on the stack, we get a stack frame like
 
+64(%rsp): Sixth argument
 56(%rsp): Fifth argument
 48(%rsp): Space for fourth argument
 40(%rsp): Space for third argument
 32(%rsp): Space for second argument
 24(%rsp): Space for first argument
 16(%rsp): Return address
-8(%rsp): Saved %rsi
-(%rsp) : Saved %rdi
+8(%rsp) : Saved %rdi
+(%rsp): Saved %rsi
+
+If, in addition, we use more than 6 %xmm registers, we push them 
+*after* %rdi (but before %rsi), so that they are stored at 16-byte
+aligned addresses.