Messages in this thread | | | Subject | Re: [PATCH V2 5/9] objtool: Add support for intra-function calls | From | Alexandre Chartre <> | Date | Wed, 8 Apr 2020 18:03:35 +0200 |
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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.
alex.
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