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Use platform-dependent mcount function #57244

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Use platform-dependent mcount function #57244

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15 changes: 14 additions & 1 deletion src/librustc_codegen_llvm/attributes.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -84,9 +84,22 @@ pub fn set_instrument_function(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value) {
if cx.sess().instrument_mcount() {
// Similar to `clang -pg` behavior. Handled by the
// `post-inline-ee-instrument` LLVM pass.

// The function name varies on platforms.
// See test/CodeGen/mcount.c in clang.
let mcount_name = if cfg!(target_os = "netbsd") {
const_cstr!("__mcount")
} else if cfg!(any(
target_arch = "mips", target_arch = "mips64",
target_arch = "powerpc", target_arch = "powerpc64")) {
const_cstr!("_mcount")
} else {
const_cstr!("mcount")
};
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This does not seem to cover it.

Looking at clang’s this->MCountName instances:

  • darwin uses \01mcount;
  • On Aarch64 if abi is gnueabi, \01_mcount is used;
  • On ARM-linux or ARM-unknown if abi is gnueabi \01__gnu_mcount_nc is used and \01mcount if not gnueabi;

Please make this a target property (specified in target files) and use that property here.

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(I used github search like this. I’m sure it missed some cases as well)


llvm::AddFunctionAttrStringValue(
llfn, llvm::AttributePlace::Function,
const_cstr!("instrument-function-entry-inlined"), const_cstr!("mcount"));
const_cstr!("instrument-function-entry-inlined"), mcount_name);
}
}

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7 changes: 7 additions & 0 deletions src/test/codegen/instrument-mcount.rs
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@@ -0,0 +1,7 @@
// ignore-tidy-linelength
// compile-flags: -Z instrument-mcount

#![crate_type = "lib"]

// CHECK: attributes #{{.*}} "instrument-function-entry-inlined"="{{_*}}mcount" "no-frame-pointer-elim"="true"
pub fn foo() {}