On Fri, May 15, 2026 at 02:08:45AM +0000, [email protected] wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s)
> to consider:
> - [Medium] The arm64 instruction decoder misclassifies trap instructions
> (e.g., `brk #0x800` used for `BUG()`) as `INSN_OTHER` instead of `INSN_BUG`.
> --
>
> commit dd63f0c03bab6a47f34cfcb310454460653638ed
> Author: Josh Poimboeuf <[email protected]>
>
> objtool/klp: Introduce objtool for arm64
>
> This commit adds basic support for arm64 in objtool, initially enabling
> only the "objtool klp" subcommands.
>
> > diff --git a/tools/objtool/arch/arm64/decode.c
> > b/tools/objtool/arch/arm64/decode.c
> > new file mode 100644
> > index 0000000000000..47658c76e1af0
> > --- /dev/null
> > +++ b/tools/objtool/arch/arm64/decode.c
>
> [ ... ]
>
> > +int arch_decode_instruction(struct objtool_file *file, const struct
> > section *sec,
> > + unsigned long offset, unsigned int maxlen,
> > + struct instruction *insn)
> > +{
>
> [ ... ]
>
> > + if (ins == 0xd503201f) {
> > + /* NOP: static branch */
> > + insn->type = INSN_NOP;
> > + } else if ((ins & 0xfc000000) == 0x14000000) {
>
> [ ... ]
>
> > + } else if ((ins & 0x7e000000) == 0x36000000) {
> > + /* TBZ/TBNZ: intra-TU sibling call */
> > + insn->type = INSN_JUMP_CONDITIONAL;
> > + insn->immediate = sign_extend64((ins >> 5) & 0x3fff, 13);
> > + } else {
> > + insn->type = INSN_OTHER;
> > + }
>
> Does this code misclassify trap instructions?
>
> On arm64, BUG() is implemented using the brk instruction (such as brk #0x800).
> Since the decoder doesn't appear to check for brk, it will fall through to the
> else block and classify it as INSN_OTHER.
>
> If INSN_BUG is misclassified as a normal instruction, won't this lose dead-end
> propagation and corrupt objtool's control-flow analysis?
Nope, as the comment above this says:
/*
* These are the bare minimum needed for static branch detection and
* checksum calculations.
*/
For arm64 we don't have any reason to care about INSN_BUG.
--
Josh
