bjoernager/rust
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Always use llvm.used for coverage symbols

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This follows what clang does in CoverageMappingGen. Using just
llvm.compiler.used is insufficient at least for MSVC targets.
This commit is contained in:
Nikita Popov 2021-08-20 21:13:18 +02:00
parent f3ae726f30
commit 306259c645
6 changed files with 59 additions and 35 deletions
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17
compiler/rustc_codegen_llvm/src/consts.rs
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@ -474,14 +474,27 @@ impl StaticMethods for CodegenCx<'ll, 'tcx> {
}
if attrs.flags.contains(CodegenFnAttrFlags::USED) {
self.add_used_global(g);
// The semantics of #[used] in Rust only require the symbol to make it into the
// object file. It is explicitly allowed for the linker to strip the symbol if it
// is dead. As such, use llvm.compiler.used instead of llvm.used.
// Additionally, https://reviews.llvm.org/D97448 in LLVM 13 started emitting unique
// sections with SHF_GNU_RETAIN flag for llvm.used symbols, which may trigger bugs
// in some versions of the gold linker.
self.add_compiler_used_global(g);
}
}
}
/// Add a global value to a list to be stored in the `llvm.compiler.used` variable, an array of i8*.
/// Add a global value to a list to be stored in the `llvm.used` variable, an array of i8*.
fn add_used_global(&self, global: &'ll Value) {
let cast = unsafe { llvm::LLVMConstPointerCast(global, self.type_i8p()) };
self.used_statics.borrow_mut().push(cast);
}
/// Add a global value to a list to be stored in the `llvm.compiler.used` variable,
/// an array of i8*.
fn add_compiler_used_global(&self, global: &'ll Value) {
let cast = unsafe { llvm::LLVMConstPointerCast(global, self.type_i8p()) };
self.compiler_used_statics.borrow_mut().push(cast);
}
}