qbe

commit 84f1e2950b3ab41523f25d205c99e9d8afd7ebba
parent 706d6beca6218caf76f0107d15e79a8f3af1646a
Author: Michael Forney <mforney@mforney.org>
Date:   Sun, 19 Apr 2020 16:31:55 -0700

arm64: Make sure SP stays aligned by 16

According to the ARMv8 overview document

  However if SP is used as the base register then the value of the stack
  pointer prior to adding any offset must be quadword (16 byte) aligned,
  or else a stack alignment exception will be generated.

This manifests as a bus error on my system.

To resolve this, just save registers two at a time with stp.

Diffstat:
M
arm64/emit.c
 | 
4
++--

1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arm64/emit.c b/arm64/emit.c
@@ -378,8 +378,8 @@ arm64_emitfn(Fn *fn, FILE *out)
 	if (e->fn->vararg) {
 		for (n=7; n>=0; n--)
 			fprintf(e->f, "\tstr\tq%d, [sp, -16]!\n", n);
-		for (n=7; n>=0; n--)
-			fprintf(e->f, "\tstr\tx%d, [sp, -8]!\n", n);
+		for (n=7; n>=0; n-=2)
+			fprintf(e->f, "\tstp\tx%d, x%d, [sp, -16]!\n", n-1, n);
 	}
 
 	if (e->frame + 16 <= 512)