On Wed, Sep 17, 2025 at 07:58:04PM +0000, Zecheng Li wrote:
> When tracking variable types, instructions that modify a pointer value
> in an untracked way can lead to incorrect type propagation. To prevent
> this, invalidate the register state when encountering such instructions.
>
> This change invalidates pointer types for various arithmetic and bitwise
> operations that current pointer offset tracking doesn't support, like
> imul, shl, and, inc, etc.
>
> A special case is added for 'xor reg, reg', which is a common idiom for
> zeroing a register. For this, the register state is updated to be a
> constant with a value of 0.
>
> This could introduce slight regressions if a variable is zeroed and then
> reused. This can be addressed in the future by using all DWARF locations
> for instruction tracking instead of only the first one.
>
> Signed-off-by: Zecheng Li <zecheng@google.com>
> ---
> tools/perf/arch/x86/annotate/instructions.c | 29 +++++++++++++++++++++
> 1 file changed, 29 insertions(+)
>
> diff --git a/tools/perf/arch/x86/annotate/instructions.c b/tools/perf/arch/x86/annotate/instructions.c
> index 709c6f7efe82..3c98f72c423f 100644
> --- a/tools/perf/arch/x86/annotate/instructions.c
> +++ b/tools/perf/arch/x86/annotate/instructions.c
> @@ -411,6 +411,35 @@ static void update_insn_state_x86(struct type_state *state,
> return;
> }
>
> + /* Invalidate register states for other ops which may change pointers */
> + if (has_reg_type(state, dst->reg1) && !dst->mem_ref &&
> + dwarf_tag(&state->regs[dst->reg1].type) == DW_TAG_pointer_type) {
> + if (!strncmp(dl->ins.name, "imul", 4) || !strncmp(dl->ins.name, "mul", 3) ||
> + !strncmp(dl->ins.name, "idiv", 4) || !strncmp(dl->ins.name, "div", 3) ||
> + !strncmp(dl->ins.name, "shl", 3) || !strncmp(dl->ins.name, "shr", 3) ||
> + !strncmp(dl->ins.name, "sar", 3) || !strncmp(dl->ins.name, "and", 3) ||
> + !strncmp(dl->ins.name, "or", 2) || !strncmp(dl->ins.name, "neg", 3) ||
> + !strncmp(dl->ins.name, "inc", 3) || !strncmp(dl->ins.name, "dec", 3)) {
> + pr_debug_dtp("%s [%x] invalidate reg%d\n",
> + dl->ins.name, insn_offset, dst->reg1);
> + state->regs[dst->reg1].ok = false;
> + state->regs[dst->reg1].copied_from = -1;
> + return;
> + }
> +
> + if (!strncmp(dl->ins.name, "xor", 3) && dst->reg1 == src->reg1) {
> + /* xor reg, reg clears the register */
> + pr_debug_dtp("xor [%x] clear reg%d\n",
> + insn_offset, dst->reg1);
> +
> + state->regs[dst->reg1].kind = TSR_KIND_CONST;
> + state->regs[dst->reg1].imm_value = 0;
> + state->regs[dst->reg1].ok = false;
I think .ok should be 'true'.
Thanks,
Namhyung
> + state->regs[dst->reg1].copied_from = -1;
> + return;
> + }
> + }
> +
> if (strncmp(dl->ins.name, "mov", 3))
> return;
>
> --
> 2.51.0.384.g4c02a37b29-goog
>