On Mon, 2023-11-20 at 16:22 -0800, Andrii Nakryiko wrote:
> Similar to special handling of STACK_ZERO, when reading 1/2/4 bytes from
> stack from slot that has register spilled into it and that register has
> a constant value zero, preserve that zero and mark spilled register as
> precise for that. This makes spilled const zero register and STACK_ZERO
> cases equivalent in their behavior.
>
> Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> ---
Acked-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
[...]
> + if (spill_cnt == size &&
> + tnum_is_const(reg->var_off) && reg->var_off.value == 0) {
> + __mark_reg_const_zero(&state->regs[dst_regno]);
> + /* this IS register fill, so keep insn_flags */
> + } else if (zero_cnt == size) {
> + /* similarly to mark_reg_stack_read(), preserve zeroes */
> + __mark_reg_const_zero(&state->regs[dst_regno]);
> + insn_flags = 0; /* not restoring original register state */
nit: In case if there would be v3, could you please
leave a comment here, something like below:
when check_stack_write_fixed_off() puts STACK_ZERO marks
for writes, not aligned on register boundary, it marks source
registers precise. Thus, additional precision propagation is
necessary in this case and insn_flags could be cleared.
or something along these lines?
> + } else {
> + mark_reg_unknown(env, state->regs, dst_regno);
> + insn_flags = 0; /* not restoring original register state */
> + }
> }
> state->regs[dst_regno].live |= REG_LIVE_WRITTEN;
> } else if (dst_regno >= 0) {
