[llvm-dev] Modify how llvm backend aligned
Sam Elliott via llvm-dev
llvm-dev at lists.llvm.org
Thu Aug 20 15:53:39 PDT 2020
You want to look for uses of the `MCBoundaryAlignFragment` class in the X86AsmBackend. This should provide some hints for how to insert alignment-specific fragments.
> On 10 Aug 2020, at 11:36 am, 郑晗 via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> I'm trying to implement something similar to sandbox(Software fault isolation).I put the protect instruction
> and danger instruction(such as call) in a basicblock and use the MachineBasicBlock::setAlignment to align it
> to 32B.The results is the picture above.but i'm wondering if it's possible to insert the no-op before the call
> instruction like the picture below.
> 0B 32B
> | some protect instruction | call instruction | no-ops |
> | some protect instruction | no-ops | call instruction |
> So is it possible to modify llvm's X86 backend to set the layout like this?(I guess google's native client achieve
> this goal, but i can't find any document.) I know there is no pass in MC layer, i just want to know if i modify
> the source code, can i achieve this goal?
> The second question, does function EmitNops in 'llvm/lib/Target/X86/MCInstLower' insert all no-ops to the binary?
> if not, which function does?
> Thanks for your help.
> zheng han
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
Software Team Lead
Senior Software Developer - LLVM and OpenTitan
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