Messages in this thread | | | Date | Wed, 1 Apr 2020 12:37:09 -0500 | From | Josh Poimboeuf <> | Subject | Re: [PATCH v2] objtool,ftrace: Implement UNWIND_HINT_RET_OFFSET |
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On Wed, Apr 01, 2020 at 07:09:10PM +0200, Peter Zijlstra wrote: > On Wed, Apr 01, 2020 at 04:43:35PM +0100, Julien Thierry wrote: > > > > +static bool has_modified_stack_frame(struct instruction *insn, struct insn_state *state) > > > { > > > + u8 ret_offset = insn->ret_offset; > > > int i; > > > > > > - if (state->cfa.base != initial_func_cfi.cfa.base || > > > - state->cfa.offset != initial_func_cfi.cfa.offset || > > > - state->stack_size != initial_func_cfi.cfa.offset || > > > - state->drap) > > > + if (state->cfa.base != initial_func_cfi.cfa.base || state->drap) > > > + return true; > > > + > > > + if (state->cfa.offset != initial_func_cfi.cfa.offset && > > > + !(ret_offset && state->cfa.offset == initial_func_cfi.cfa.offset + ret_offset)) > > > > Isn't that the same thing as "state->cfa.offset != > > initial_func_cfi.cfa.offset + ret_offset" ? > > I'm confused on what cfa.offset is, sometimes it increase with > stack_size, sometimes it doesn't. > > ISTR that for the ftrace case it was indeed cfa.offset + 8, but for the > IRET case below (where it is now not used anymore) it was cfa.offset > (not cfa.offset + 40, which I was expecting).
It depends on the value of cfa.base. If cfa.base is CFI_SP, then cfa.offset changes with stack_size. If cfa.base is CFI_BP (i.e. if the function uses a frame pointer), then cfa.offset is constant (the distance between RBP on the stack and the previous frame).
-- Josh
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