Messages in this thread | | | Subject | Re: [PATCH V2 5/9] objtool: Add support for intra-function calls | From | Julien Thierry <> | Date | Wed, 8 Apr 2020 17:04:46 +0100 |
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On 4/8/20 5:03 PM, Alexandre Chartre wrote: > > > On 4/8/20 4:19 PM, Julien Thierry wrote: >> >> >> On 4/8/20 3:06 PM, Alexandre Chartre wrote: >>> >>> >>> On 4/7/20 3:28 PM, Alexandre Chartre wrote: >>>> >>>> On 4/7/20 3:07 PM, Peter Zijlstra wrote: >>>>> On Tue, Apr 07, 2020 at 09:31:38AM +0200, Alexandre Chartre wrote: >>>>> >>>>>> index a62e032863a8..7ee1561bf7ad 100644 >>>>>> --- a/tools/objtool/arch/x86/decode.c >>>>>> +++ b/tools/objtool/arch/x86/decode.c >>>>>> @@ -497,3 +497,15 @@ void arch_initial_func_cfi_state(struct >>>>>> cfi_state *state) >>>>>> state->regs[16].base = CFI_CFA; >>>>>> state->regs[16].offset = -8; >>>>>> } >>>>>> + >>>>>> + >>>>>> +void arch_configure_intra_function_call(struct stack_op *op) >>>>>> +{ >>>>>> + /* >>>>>> + * For the impact on the stack, make an intra-function >>>>>> + * call behaves like a push of an immediate value (the >>>>>> + * return address). >>>>>> + */ >>>>>> + op->src.type = OP_SRC_CONST; >>>>>> + op->dest.type = OP_DEST_PUSH; >>>>>> +} >>>>> >>>>> An alternative is to always set up stack ops for CALL/RET on >>>>> decode, but >>>>> conditionally run update_insn_state() for them. >>>>> >>>>> Not sure that makes more logical sense, but the patch would be >>>>> simpler I >>>>> think. >>>> >>>> Right, this would avoid adding a new arch dependent function and the >>>> patch >>>> will be simpler. This probably makes sense as the stack impact is >>>> the same >>>> for all calls (but objtool will use it only for intra-function calls). >>>> >>> >>> Actually the processing of the ret instruction is more complicated >>> than I >>> anticipated with intra-function calls, and so my implementation is not >>> complete at the moment. >>> >>> The issue is to correctly handle how the ret is going to behave >>> depending how >>> the stack (or register on arm) is modified before the ret. Adjusting >>> the stack >>> offset makes the stack state correct, but objtool still needs to >>> correctly >>> figure out where the ret is going to return and where the code flow >>> continues. >>> >> >> A hint indicating the target "jump" address could be useful. It could >> be used to add the information on some call/jump dynamic that aren't >> associated with jump tables. Currently when objtool finds a jump >> dynamic, if no branches were added to it, it will just return. >> >> Having such a hint could help make additional links (at least on >> arm64). I don't know what Peter and Josh would think of that (if that >> helps in your case of course). >> > > Yes, I am thinking about tracking intra-function call return address, > and having hints to specify a return address changes. For example, > on x86, when we push the branch address on the stack we overwrite the > last return address (the return address of the last intra-function call). > Then the return instruction can figure out where to branch.
I see, I was thinking about a more generic hint, that would just indicate "this instruction actually jumps here". So in your case it would just point that a certain return instruction causes to branch somewhere.
This way the hint could also be used for other instructions (e.g. INSN_JUMP_DYNAMIC).
-- Julien Thierry
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