[PATCH] D42839: [MC] Allow overriding whether to output Elf_Rel or Elf_Rela relocations

[Rafael Avila de Espindola via llvm-commits]

Alexander Richardson via Phabricator <reviews at reviews.llvm.org> writes:

> Index: lib/MC/MCELFObjectTargetWriter.cpp
> ===================================================================
> --- lib/MC/MCELFObjectTargetWriter.cpp
> +++ lib/MC/MCELFObjectTargetWriter.cpp
> @@ -8,14 +8,40 @@
>  //===----------------------------------------------------------------------===//
>  
>  #include "llvm/MC/MCELFObjectWriter.h"
> +#include "llvm/Support/CommandLine.h"
>  
>  using namespace llvm;
>  
> +enum class ELFRelocationFormat { Default, Rel, Rela };
> +static cl::opt<ELFRelocationFormat> RelocationFormat(
> +    "elf-relocation-format",
> +    cl::desc("Select whether to use REL or "
> +             "RELA for relocations in the output object"),
> +    cl::values(clEnumValN(ELFRelocationFormat::Default, "default",
> +                          "Use the default kind for the current target"),
> +               clEnumValN(ELFRelocationFormat::Rel, "rel",
> +                          "Always emit REL relocations"),
> +               clEnumValN(ELFRelocationFormat::Rela, "rela",
> +                          "Always emit RELA relocations")),
> +    cl::init(ELFRelocationFormat::Default), cl::Hidden);
> +
> +static bool shouldUseRelocationAddend(bool Default) {
> +  switch (RelocationFormat) {
> +  case ELFRelocationFormat::Rel:
> +    return false;
> +  case ELFRelocationFormat::Rela:
> +    return true;
> +  default:
> +    return Default;
> +  }
> +}

Do you need to be able to force the use of Elf_Rel?

The only non test uses I can think of require forcing a target that
normally uses Elf_Rel to use Elf_Rela.


>  MCELFObjectTargetWriter::MCELFObjectTargetWriter(bool Is64Bit_, uint8_t OSABI_,
>                                                   uint16_t EMachine_,
>                                                   bool HasRelocationAddend_)
>      : OSABI(OSABI_), EMachine(EMachine_),
> -      HasRelocationAddend(HasRelocationAddend_), Is64Bit(Is64Bit_) {}
> +      HasRelocationAddend(shouldUseRelocationAddend(HasRelocationAddend_)),
> +      Is64Bit(Is64Bit_) {}


You should probably move the option up the call chain and just pass the
final values of HasRelocationAddend_ to the constructor.

Cheers,
Rafael