Messages in this thread | | | Date | Thu, 13 Apr 2023 12:30:48 -0700 | From | Josh Poimboeuf <> | Subject | Re: [PATCH 3/3] objtool: Generate ORC data for __pfx code |
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On Thu, Apr 13, 2023 at 09:24:49PM +0200, Peter Zijlstra wrote: > On Thu, Apr 13, 2023 at 08:29:33AM -0700, Josh Poimboeuf wrote: > > On Thu, Apr 13, 2023 at 01:24:26PM +0200, Peter Zijlstra wrote: > > > > + if (!insn->cfi) { > > > > + /* > > > > + * This can happen if stack validation isn't enabled or the > > > > + * function is annotated with STACK_FRAME_NON_STANDARD. > > > > + */ > > > > + return 0; > > > > + } > > > > + > > > > + /* Propagate insn->cfi to the prefix code */ > > > > + cfi = cfi_hash_find_or_add(insn->cfi); > > > > + for (; prev != insn; prev = next_insn_same_sec(file, prev)) > > > > + prev->cfi = cfi; > > > > + > > > > return 0; > > > > } > > > > > > FWIW, this makes the whole thing hard rely on the prefix being single > > > byte NOPs -- which they are, but perhaps we should assert this? > > > > Couldn't they be any stack-invariant instructions? > > Hmm, I was thikning that since we don't know the size of the > instructions being written, we need CFI for all offsets. But perhaps, > since we do a left-match on IP, only one entry at the __pfx+0 location > would work?
Right, while in objtool (almost) every insn has insn->cfi, the actual ORC entries only get created at the boundaries of change.
-- Josh
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