On 6/1/20 2:52 PM, Jakub Jelinek wrote:
On Mon, Jun 01, 2020 at 02:28:51PM +0200, Martin Liška wrote:
--- a/gcc/asan.c
+++ b/gcc/asan.c
@@ -1598,8 +1598,24 @@ asan_emit_stack_protection (rtx base, rtx pbase,
unsigned int alignb,
if (use_after_return_class < 5
&& can_store_by_pieces (sz, builtin_memset_read_str, &c,
BITS_PER_UNIT, true))
- store_by_pieces (shadow_mem, sz, builtin_memset_read_str, &c,
- BITS_PER_UNIT, true, RETURN_BEGIN);
+ {
+ /* Emit:
+ memset(ShadowBase, kAsanStackAfterReturnMagic, ShadowSize);
+ **SavedFlagPtr(FakeStack) = 0
+ */
+ store_by_pieces (shadow_mem, sz, builtin_memset_read_str, &c,
+ BITS_PER_UNIT, true, RETURN_BEGIN);
+
+ unsigned HOST_WIDE_INT offset
+ = (1 << (use_after_return_class + 6));
+ offset -= GET_MODE_SIZE (ptr_mode);
+ mem = adjust_address (mem, Pmode, offset);
+ mem = gen_rtx_MEM (ptr_mode, mem);
+ rtx tmp_reg = gen_reg_rtx (Pmode);
+ emit_move_insn (tmp_reg, mem);
+ mem = adjust_address (mem, QImode, 0);
+ emit_move_insn (mem, const0_rtx);
This doesn't look correct to me.
I'd think the first adjust_address should be
mem = adjust_address (mem, ptr_mode, offset);
which will give you a MEM with ptr_mode which has SavedFlagPtr(FakeStack)
address, i.e. *SavedFlagPtr(FakeStack).
Next, you want to load that into some temporary, so e.g.
rtx addr = gen_reg_rtx (ptr_mode);
emit_move_insn (addr, mem);
next you need to convert that ptr_mode to Pmode if needed, so something like
addr = convert_memory_address (Pmode, addr);
and finally:
mem = gen_rtx_MEM (QImode, addr);
emit_move_insn (mem, const0_rtx);
Completely untested.
This is not correct. With your suggestion I have:
int foo(int index)
{
int a[100];
return a[index];
}
$ diff -u before.s after.s
--- before.s 2020-06-01 15:15:22.634337654 +0200
+++ after.s 2020-06-01 15:16:32.205711511 +0200
@@ -81,8 +81,7 @@
movq %rdi, 2147450920(%rax)
movq %rsi, 2147450928(%rax)
movq %rdi, 2147450936(%rax)
- movq 504(%rbx), %rax
- movb $0, (%rax)
+ movb $0, 504(%rbx)
jmp .L3
.L2:
movq $0, 2147450880(%rax)
There's missing one level of de-reference. Looking at clang:
movq %rsi, 2147450928(%rax)
movq %rdi, 2147450936(%rax)
movq 504(%rbx), %rax
movb $0, (%rax)
jmp .L3
.L2:
It does the same as my patch.
Martin
Jakub
