On Wed, Jun 10, 2020 at 11:49:01AM +0200, Martin Liška wrote:
> - 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
SavedFlagPtr has two arguments, doesn't it?
> + */
> + 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);
So, mem here is a MEM into which we stored ASAN_STACK_RETIRED_MAGIC.
> + mem = adjust_address (mem, ptr_mode, offset);
This adds offset to it and changes mode to ptr_mode. So,
mem is now *(ptr_mode)(&old_mem + offset)
> + rtx addr = gen_reg_rtx (ptr_mode);
> + emit_move_insn (addr, mem);
We load that value.
> + mem = gen_rtx_MEM (ptr_mode, addr);
> + mem = adjust_address (mem, QImode, 0);
And here I'm lost why you do that. If you want to store a single
byte into what it points to, then why don't you just
mem = gen_rtx_MEM (QImode, addr);
instead of the above two lines?
adjust_address will return a MEM like the above, with offset not adjusted
(as the addition is 0) and mode changed to QImode, but there is no reason
not to create it already in QImode.
> + emit_move_insn (mem, const0_rtx);
> + }
> else if (use_after_return_class >= 5
> || !set_storage_via_setmem (shadow_mem,
> GEN_INT (sz),
> --
> 2.26.2
>
Jakub
