s390x: Enable object backend #4680
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This enables the object backend for s390x, in particular the processing of all required relocations. This uncovered a bug: we need to use PLT relocations for the target of calls, which we currently do not. Fixed by adding a new S390xPLTRel32Dbl reloc type and using it where needed.
bjorn3
reviewed
Aug 10, 2022
| @@ -3216,7 +3216,7 @@ impl MachInstEmit for Inst { | |||
| } | |||
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| let opcode = 0xc05; // BRASL | |||
| let reloc = Reloc::S390xPCRel32Dbl; | |||
| let reloc = Reloc::S390xPLTRel32Dbl; | |||
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I think this should check is_colocated and use PCRel if true. That is faster than going through the PLT.
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That's not really necessary; the JIT backend doesn't use PLTs anyway, and when generating object files, the linker will omit PLTs when they are not needed. LLVM also always emits PLT relocations and relies on the linker to optimize them away.
cfallin
approved these changes
Aug 10, 2022
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This enables the object backend for s390x, in particular the
processing of all required relocations.
This uncovered a bug: we need to use PLT relocations for the
target of calls, which we currently do not. Fixed by adding
a new S390xPLTRel32Dbl reloc type and using it where needed.
FYI - @cfallin @bjorn3