On Sat, Jul 11, 2026 at 08:24:08AM +0800, H.J. Lu wrote:
> All stack variables do have the proper alignments. But when
> we allocate ASAN red zone aligned with ASAN alignment on
> stack, we don't take alignments of stack variables into account.
> When a stack variable alignment > ASAN alignment, it has the
> wrong alignment at run-time since ASAN red zone size on the
> stack is only aligned to ASAN alignment. My patch pads ASAN
> red zone so that ASAN red zone size is aligned to
>
> MAX (ASAN alignment, alignments of stack variables)
This makes no sense.
All the variables tracked by ASAN have their proper
stack_vars[i].alignb (which better should be accurate)
and are allocated such that they have in between them
appropriate red zone and the alignments are taken into
accoiunt.
Now, in the PR120201 testcase, it seems alignb of the
only VAR_DECL in there (transform) is 16 bytes, but
stack_alignment_needed got increased to 512 bits (i.e.
64 bytes) not because of that var, but because of
a SSA_NAME with a V64QI type through
expand_one_ssa_partition -> record_alignment_for_reg_var (512).
So, that extra alignment is not something needed for every single
var in the expand_stack_vars layout, it is for other stack
allocations done later on, right?
>From this your first hunk definitely looks completely unnecessary.
If you have a stack frame with 64 single byte vars and
stack_alignment_needed 512 because there is some V64QI SSA_NAME,
why should every single of those 64 vars be aligned to 64 bytes?
One should be able to align them solely because of their alignment.
If you need the extra alignment for later allocations, all that
is needed is to make sure the whole thing is aligned.
So, perhaps somewhere around your second hunk, make
data.asan_alignb max of its former value and
stack_alignment_needed / BITS_PER_UNIT, such that
if (data.asan_alignb > ASAN_RED_ZONE_SIZE
&& data.asan_alignb <= 4096
&& sz + ASAN_RED_ZONE_SIZE >= (int) data.asan_alignb)
redzonesz = ((sz + ASAN_RED_ZONE_SIZE + data.asan_alignb - 1)
& ~(data.asan_alignb - HOST_WIDE_INT_1)) - sz;
will take it into account?
Jakub
