On Tue, May 05, 2026 at 10:56:58AM -0500, Segher Boessenkool wrote:
> Hi!
>
> On Tue, May 05, 2026 at 04:45:39PM +0200, Peter Zijlstra wrote:
> > On Tue, May 05, 2026 at 02:16:23PM +0530, Sathvika Vasireddy wrote:
> > > switch (opcode) {
> > > + case 16:
> >
> > Like case 18 below, this wants a comment describing which instruction
> > this is; bclr ?
>
> Yes. It is 19/16, b[c]lr (primary opcode 19, secondary opcode 16).
>
> Where is it described what INSN_RETURN actually means for objtool? Not
> in the header file :-(
Yeah, nowhere much I'm afraid, it is very much organic growth that is
firmly rooted in x86.
RETURN, along with sibling/tail CALLs validate things like the stack
frame being in identical state as on function entry and a few other
sanity checks (DF flag not set, no uaccess).
There is also a pile of hacks around the whole return thunk mitigation
thing. But that might be less relevant for other archs.
