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 15:19:58 +0100 |
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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).
-- Julien Thierry
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