[PATCH] Add missing store in emission of asan_stack_free.

[Jakub Jelinek]

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.

	Jakub