Messages in this thread |  | | Date | Wed, 6 May 2026 09:00:00 +0200 | | From | Peter Zijlstra <> | | Subject | Re: [PATCH v1 1/6] objtool/powerpc: Add build-time fixup of alternate feature branch targets |
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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.
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