From cd095a44db262351b09ea144a44b76e22d62c77a Mon Sep 17 00:00:00 2001
From: Quentin Carbonneaux <quentin@c9x.me>
Date: Mon, 8 Nov 2021 10:46:20 +0100
Subject: [PATCH] fix for sloppy reg->mem in arm64 abi
Michael found a bug where some copies
from registers to memory in the arm64
abi clobber the stack. The test case
is:
type :T = { w }
function w $f() {
@start
%p =:T call $g()
%x =w loadw %p
ret %x
}
qbe will write 4 bytes out of bounds
when pulling the result struct from
its register. The same bug can be
observed if :T's definition is {w 3};
in this case qbe writes 16 bytes in
a slot of 12 bytes.
This patch changes stkblob() to use
the rounded argument size if it is
going to be restored from registers.
Relatedly, mem->reg loads for structs
with size < 16 and != 8, are treated
a bit sloppily both in the arm64 and
in the sysv abis. That is much less
harmful than the present bug.
---
arm64/abi.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/arm64/abi.c b/arm64/abi.c
index 8209944..f37c892 100644
--- a/arm64/abi.c
+++ b/arm64/abi.c
@@ -312,12 +312,14 @@ stkblob(Ref r, Class *c, Fn *fn, Insl **ilp)
{
Insl *il;
int al;
+ uint64_t sz;
il = alloc(sizeof *il);
al = c->t->align - 2; /* NAlign == 3 */
if (al < 0)
al = 0;
- il->i = (Ins){Oalloc+al, Kl, r, {getcon(c->t->size, fn)}};
+ sz = c->class & Cptr ? c->t->size : c->size;
+ il->i = (Ins){Oalloc+al, Kl, r, {getcon(sz, fn)}};
il->link = *ilp;
*ilp = il;
}