[llvm-dev] llvm-mc assembler, GNU as, and pc-relative branches for Arm/AArch64/Mips

Rafael Avila de Espindola via llvm-dev llvm-dev at lists.llvm.org
Wed Jan 10 09:45:08 PST 2018

Alex Bradbury via llvm-dev <llvm-dev at lists.llvm.org> writes:

> # Summary
> As a consequence of comparing the RISC-V LLVM MC assembler to the RISC-V GNU
> assembler I've noticed that a number of targets have quite different handling
> for pc-relative jumps/branches with immediate integer operands in llvm-mc vs
> GNU as. I'll admit that this isn't likely to occur in hand-written code (as
> you'd almost always prefer to use a label), but thought it was worth slightly
> wider discussion. See below for full details, but really it boils down to
> whether you treat an immediate offset to a pc-relative branch as an absolute
> target or a pc-relative offset to be directly encoded in the instruction.

It sounds like a bug. Note that for X86_64 we produce relocations like

        jmp 0x123


000000000001  000000000002 R_X86_64_PC32                        11f


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