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Rollup merge of #113497 - xSetech:mips_32_abi, r=davidtwco

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Support explicit 32-bit MIPS ABI for the synthetic object

PR #95604 introduced a "synthetic object file to ensure all exported and used symbols participate in the linking". One constraint on this file is that for MIPS-based targets, its architecture-specific ELF flags must be the same as all other object files passed to the linker. That's enforced by LLD, here:
https://github.com/llvm/llvm-project/blob/llvmorg-16.0.6/lld/ELF/Arch/MipsArchTree.cpp#L77

The current approach to determining e_flags for 32-bit was implemented in PR #96930, which links to this issue that summarizes the problem well: https://github.com/ayrtonm/psx-sdk-rs/issues/9

> ... the temporary object file is created with an e_flags which is
> invalid for 32-bit MIPS targets. The main issue is that it omits the ABI
> bits (EF_MIPS_ABI_O32) which implies it uses the N64 ABI.

To enable the N32 MIPS ABI (which succeeded O32), this patch enables setting the synthetic object's ABI based on the target "llvm-abiname" field, if it's given; otherwise, the O32 ABI is assumed for 32-bit MIPS targets.

More information about the N32 ABI can be found here: https://web.archive.org/web/20160121005457/http://techpubs.sgi.com/library/manuals/2000/007-2816-005/pdf/007-2816-005.pdf
This commit is contained in:
Matthias Krüger 2023-07-11 17:46:19 +02:00 committed by GitHub
commit 685ba08693
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1 changed files with 10 additions and 2 deletions
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12
compiler/rustc_codegen_ssa/src/back/metadata.rs
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@ -243,8 +243,16 @@ pub(crate) fn create_object_file(sess: &Session) -> Option<write::Object<'static
s if s.contains("r6") => elf::EF_MIPS_ARCH_32R6,
_ => elf::EF_MIPS_ARCH_32R2,
};
// The only ABI LLVM supports for 32-bit MIPS CPUs is o32.
let mut e_flags = elf::EF_MIPS_CPIC | elf::EF_MIPS_ABI_O32 | arch;
let mut e_flags = elf::EF_MIPS_CPIC | arch;
// If the ABI is explicitly given, use it or default to O32.
match sess.target.options.llvm_abiname.to_lowercase().as_str() {
"n32" => e_flags |= elf::EF_MIPS_ABI2,
"o32" => e_flags |= elf::EF_MIPS_ABI_O32,
_ => e_flags |= elf::EF_MIPS_ABI_O32,
};
if sess.target.options.relocation_model != RelocModel::Static {
e_flags |= elf::EF_MIPS_PIC;
}