On Thu, Oct 11, 2012 at 01:14:31PM -0400, Diego Novillo wrote:
> On 2012-10-11 12:38 , Jakub Jelinek wrote:
>
> >- gimple_seq seq, stmts;
> >- tree shadow_type = size_in_bytes == 16 ?
> >- short_integer_type_node : char_type_node;
> >- tree shadow_ptr_type = build_pointer_type (shadow_type);
> >- tree uintptr_type = lang_hooks.types.type_for_mode (ptr_mode,
> >- /*unsignedp=*/true);
> >+ tree shadow_ptr_type = shadow_ptr_types[size_in_bytes == 16];
>
> Add '? 1 : 0' in the array index expression.
Ok.
> > /* Build
> >- (base_addr >> ASAN_SHADOW_SHIFT) | targetm.asan_shadow_offset (). */
> >+ (base_addr >> ASAN_SHADOW_SHIFT) + targetm.asan_shadow_offset (). */
>
> Hm, I wonder if this is a documentation problem or we're generating
> bad runtime code. Wei, you tested the runtime and it was working
> with the GCC generated code, right?
The asan web pages document |, the old tree-asan.c emitted +, I've changed
it to BIT_IOR_EXPR, but that resulted in worse assembly, and I believe at
least for the current x86_64 and i686 address ranges and shadow offset
values it actually doesn't matter.
On x86_64 stack is like 0x7ffff6e00000, shifted down by 3 is still smaller
than 1L << 44 that is ored or added to it. And the negative half of the
address space is used by the kernel, nothing is mapped into it (besides
vsyscall page) and neither | nor + of 1L << 44 to it would work well.
On i386, | and + works the same for all addresses, as 0xffffffffU >> 3
is still smaller than 1 << 29.
The reason why + generates better code on x86_64/i686 is that one can use
e.g. movzbl (%r1, %r2), %r3 instead of orq %r2, %r1; movzb (%r1), %r3.
> >+ if (shadow_ptr_types[0] == NULL_TREE)
> >+ {
> >+ alias_set_type set = new_alias_set ();
> >+ shadow_ptr_types[0]
> >+ = build_distinct_type_copy (unsigned_char_type_node);
> >+ TYPE_ALIAS_SET (shadow_ptr_types[0]) = set;
> >+ shadow_ptr_types[0] = build_pointer_type (shadow_ptr_types[0]);
> >+ shadow_ptr_types[1]
> >+ = build_distinct_type_copy (short_unsigned_type_node);
> >+ TYPE_ALIAS_SET (shadow_ptr_types[1]) = set;
> >+ shadow_ptr_types[1] = build_pointer_type (shadow_ptr_types[1]);
> >+ }
>
> Move this to an initialization function, please.
Okay.
Jakub
