Rollup merge of #59506 - JohnTitor:improve-mcount, r=nagisa

Use platform dependent mcount function

close #59097

This pull-request is based on #57244 and [here](https://github.com/llvm-mirror/clang/search?q=MCountName&unscoped_MCountName).

r? @nagisa

src/librustc_codegen_llvm/attributes.rs

@@ -77,9 +77,15 @@ 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 = CString::new(
+            cx.sess().target.target.options.target_mcount.as_str().as_bytes()).unwrap();
+
         llvm::AddFunctionAttrStringValue(
             llfn, llvm::AttributePlace::Function,
-            const_cstr!("instrument-function-entry-inlined"), const_cstr!("mcount"));
+            const_cstr!("instrument-function-entry-inlined"), &mcount_name);
     }
 }
 

src/librustc_target/spec/aarch64_unknown_linux_gnu.rs

@@ -17,6 +17,7 @@ pub fn target() -> TargetResult {
         linker_flavor: LinkerFlavor::Gcc,
         options: TargetOptions {
             abi_blacklist: super::arm_base::abi_blacklist(),
+            target_mcount: "\u{1}_mcount".to_string(),
             .. base
         },
     })

src/librustc_target/spec/aarch64_unknown_linux_musl.rs

@@ -17,6 +17,7 @@ pub fn target() -> TargetResult {
         linker_flavor: LinkerFlavor::Gcc,
         options: TargetOptions {
             abi_blacklist: super::arm_base::abi_blacklist(),
+            target_mcount: "\u{1}_mcount".to_string(),
             .. base
         },
     })

src/librustc_target/spec/aarch64_unknown_netbsd.rs

@@ -1,4 +1,4 @@
-use crate::spec::{LinkerFlavor, Target, TargetResult};
+use crate::spec::{LinkerFlavor, Target, TargetOptions, TargetResult};
 
 pub fn target() -> TargetResult {
     let mut base = super::netbsd_base::opts();
@@ -16,6 +16,9 @@ pub fn target() -> TargetResult {
         target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
-        options: base,
+        options: TargetOptions {
+            target_mcount: "__mcount".to_string(),
+            .. base
+        },
     })
 }

src/librustc_target/spec/arm_unknown_linux_gnueabi.rs

@@ -18,6 +18,7 @@ pub fn target() -> TargetResult {
         options: TargetOptions {
             features: "+strict-align,+v6".to_string(),
             abi_blacklist: super::arm_base::abi_blacklist(),
+            target_mcount: "\u{1}__gnu_mcount_nc".to_string(),
             .. base
         },
     })

src/librustc_target/spec/arm_unknown_linux_gnueabihf.rs

@@ -18,6 +18,7 @@ pub fn target() -> TargetResult {
         options: TargetOptions {
             features: "+strict-align,+v6,+vfp2".to_string(),
             abi_blacklist: super::arm_base::abi_blacklist(),
+            target_mcount: "\u{1}__gnu_mcount_nc".to_string(),
             .. base
         }
     })

src/librustc_target/spec/arm_unknown_linux_musleabi.rs

@@ -23,6 +23,7 @@ pub fn target() -> TargetResult {
         linker_flavor: LinkerFlavor::Gcc,
         options: TargetOptions {
             abi_blacklist: super::arm_base::abi_blacklist(),
+            target_mcount: "\u{1}mcount".to_string(),
             .. base
         },
     })

src/librustc_target/spec/arm_unknown_linux_musleabihf.rs

@@ -23,6 +23,7 @@ pub fn target() -> TargetResult {
         linker_flavor: LinkerFlavor::Gcc,
         options: TargetOptions {
             abi_blacklist: super::arm_base::abi_blacklist(),
+            target_mcount: "\u{1}mcount".to_string(),
             .. base
         },
     })

src/librustc_target/spec/armv4t_unknown_linux_gnueabi.rs

@@ -19,6 +19,7 @@ pub fn target() -> TargetResult {
             // Atomic operations provided by compiler-builtins
             max_atomic_width: Some(32),
             abi_blacklist: super::arm_base::abi_blacklist(),
+            target_mcount: "\u{1}__gnu_mcount_nc".to_string(),
             .. base
         }
     })

src/librustc_target/spec/armv5te_unknown_linux_gnueabi.rs

@@ -19,6 +19,7 @@ pub fn target() -> TargetResult {
             // Atomic operations provided by compiler-builtins
             max_atomic_width: Some(32),
             abi_blacklist: super::arm_base::abi_blacklist(),
+            target_mcount: "\u{1}__gnu_mcount_nc".to_string(),
             .. base
         }
     })

src/librustc_target/spec/armv5te_unknown_linux_musleabi.rs

@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
             // Atomic operations provided by compiler-builtins
             max_atomic_width: Some(32),
             abi_blacklist: super::arm_base::abi_blacklist(),
+            target_mcount: "\u{1}mcount".to_string(),
             .. base
         }
     })

src/librustc_target/spec/armv6_unknown_freebsd.rs

@@ -18,6 +18,7 @@ pub fn target() -> TargetResult {
             features: "+v6,+vfp2".to_string(),
             max_atomic_width: Some(64),
             abi_blacklist: super::arm_base::abi_blacklist(),
+            target_mcount: "\u{1}__gnu_mcount_nc".to_string(),
             .. base
         }
     })

src/librustc_target/spec/armv6_unknown_netbsd_eabihf.rs

@@ -18,6 +18,7 @@ pub fn target() -> TargetResult {
         options: TargetOptions {
             features: "+v6,+vfp2".to_string(),
             abi_blacklist: super::arm_base::abi_blacklist(),
+            target_mcount: "__mcount".to_string(),
             .. base
         }
     })

src/librustc_target/spec/armv7_unknown_cloudabi_eabihf.rs

@@ -1,4 +1,4 @@
-use crate::spec::{LinkerFlavor, Target, TargetResult};
+use crate::spec::{LinkerFlavor, Target, TargetOptions, TargetResult};
 
 pub fn target() -> TargetResult {
     let mut base = super::cloudabi_base::opts();
@@ -19,6 +19,9 @@ pub fn target() -> TargetResult {
         target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
-        options: base,
+        options: TargetOptions {
+            target_mcount: "\u{1}mcount".to_string(),
+            .. base
+        },
     })
 }

src/librustc_target/spec/armv7_unknown_freebsd.rs

@@ -18,6 +18,7 @@ pub fn target() -> TargetResult {
             features: "+v7,+vfp3,+d16,+thumb2,-neon".to_string(),
             max_atomic_width: Some(64),
             abi_blacklist: super::arm_base::abi_blacklist(),
+            target_mcount: "\u{1}__gnu_mcount_nc".to_string(),
             .. base
         }
     })

src/librustc_target/spec/armv7_unknown_linux_gnueabihf.rs

@@ -23,6 +23,7 @@ pub fn target() -> TargetResult {
             cpu: "generic".to_string(),
             max_atomic_width: Some(64),
             abi_blacklist: super::arm_base::abi_blacklist(),
+            target_mcount: "\u{1}__gnu_mcount_nc".to_string(),
             .. base
         }
     })

src/librustc_target/spec/armv7_unknown_linux_musleabihf.rs

@@ -26,6 +26,7 @@ pub fn target() -> TargetResult {
             cpu: "generic".to_string(),
             max_atomic_width: Some(64),
             abi_blacklist: super::arm_base::abi_blacklist(),
+            target_mcount: "\u{1}mcount".to_string(),
             .. base
         }
     })

src/librustc_target/spec/armv7_unknown_netbsd_eabihf.rs

@@ -19,6 +19,7 @@ pub fn target() -> TargetResult {
             cpu: "generic".to_string(),
             max_atomic_width: Some(64),
             abi_blacklist: super::arm_base::abi_blacklist(),
+            target_mcount: "__mcount".to_string(),
             .. base
         }
     })

src/librustc_target/spec/i686_apple_darwin.rs

@@ -1,4 +1,4 @@
-use crate::spec::{LinkerFlavor, Target, TargetResult};
+use crate::spec::{LinkerFlavor, Target, TargetOptions, TargetResult};
 
 pub fn target() -> TargetResult {
     let mut base = super::apple_base::opts();
@@ -19,6 +19,9 @@ pub fn target() -> TargetResult {
         target_env: String::new(),
         target_vendor: "apple".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
-        options: base,
+        options: TargetOptions {
+            target_mcount: "\u{1}mcount".to_string(),
+            .. base
+        },
     })
 }

src/librustc_target/spec/i686_unknown_netbsd.rs

@@ -1,4 +1,4 @@
-use crate::spec::{LinkerFlavor, Target, TargetResult};
+use crate::spec::{LinkerFlavor, Target, TargetOptions, TargetResult};
 
 pub fn target() -> TargetResult {
     let mut base = super::netbsd_base::opts();
@@ -18,6 +18,9 @@ pub fn target() -> TargetResult {
         target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
-        options: base,
+        options: TargetOptions {
+            target_mcount: "__mcount".to_string(),
+            .. base
+        },
     })
 }

src/librustc_target/spec/mips64_unknown_linux_gnuabi64.rs

@@ -17,6 +17,7 @@ pub fn target() -> TargetResult {
             cpu: "mips64r2".to_string(),
             features: "+mips64r2".to_string(),
             max_atomic_width: Some(64),
+            target_mcount: "_mcount".to_string(),
 
             ..super::linux_base::opts()
         },

src/librustc_target/spec/mips64el_unknown_linux_gnuabi64.rs

@@ -17,6 +17,7 @@ pub fn target() -> TargetResult {
             cpu: "mips64r2".to_string(),
             features: "+mips64r2".to_string(),
             max_atomic_width: Some(64),
+            target_mcount: "_mcount".to_string(),
 
             ..super::linux_base::opts()
         },

src/librustc_target/spec/mips_unknown_linux_gnu.rs

@@ -16,6 +16,7 @@ pub fn target() -> TargetResult {
             cpu: "mips32r2".to_string(),
             features: "+mips32r2,+fpxx,+nooddspreg".to_string(),
             max_atomic_width: Some(32),
+            target_mcount: "_mcount".to_string(),
 
             ..super::linux_base::opts()
         },

src/librustc_target/spec/mips_unknown_linux_musl.rs

@@ -1,4 +1,4 @@
-use crate::spec::{LinkerFlavor, Target, TargetResult};
+use crate::spec::{LinkerFlavor, Target, TargetOptions, TargetResult};
 
 pub fn target() -> TargetResult {
     let mut base = super::linux_musl_base::opts();
@@ -17,6 +17,9 @@ pub fn target() -> TargetResult {
         target_env: "musl".to_string(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
-        options: base,
+        options: TargetOptions {
+            target_mcount: "_mcount".to_string(),
+            .. base
+        },
     })
 }

src/librustc_target/spec/mips_unknown_linux_uclibc.rs

@@ -16,6 +16,7 @@ pub fn target() -> TargetResult {
             cpu: "mips32r2".to_string(),
             features: "+mips32r2,+soft-float".to_string(),
             max_atomic_width: Some(32),
+            target_mcount: "_mcount".to_string(),
 
             ..super::linux_base::opts()
         },

src/librustc_target/spec/mipsel_unknown_linux_gnu.rs

@@ -17,6 +17,7 @@ pub fn target() -> TargetResult {
             cpu: "mips32r2".to_string(),
             features: "+mips32r2,+fpxx,+nooddspreg".to_string(),
             max_atomic_width: Some(32),
+            target_mcount: "_mcount".to_string(),
 
             ..super::linux_base::opts()
         },

src/librustc_target/spec/mipsel_unknown_linux_musl.rs

@@ -1,4 +1,4 @@
-use crate::spec::{LinkerFlavor, Target, TargetResult};
+use crate::spec::{LinkerFlavor, Target, TargetOptions, TargetResult};
 
 pub fn target() -> TargetResult {
     let mut base = super::linux_musl_base::opts();
@@ -17,6 +17,9 @@ pub fn target() -> TargetResult {
         target_env: "musl".to_string(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
-        options: base,
+        options: TargetOptions {
+            target_mcount: "_mcount".to_string(),
+            .. base
+        },
     })
 }

src/librustc_target/spec/mipsel_unknown_linux_uclibc.rs

@@ -17,6 +17,7 @@ pub fn target() -> TargetResult {
             cpu: "mips32r2".to_string(),
             features: "+mips32r2,+soft-float".to_string(),
             max_atomic_width: Some(32),
+            target_mcount: "_mcount".to_string(),
 
             ..super::linux_base::opts()
         },

src/librustc_target/spec/mipsisa32r6_unknown_linux_gnu.rs

@@ -16,6 +16,7 @@ pub fn target() -> TargetResult {
             cpu: "mips32r6".to_string(),
             features: "+mips32r6".to_string(),
             max_atomic_width: Some(32),
+            target_mcount: "_mcount".to_string(),
 
             ..super::linux_base::opts()
         },

src/librustc_target/spec/mipsisa32r6el_unknown_linux_gnu.rs

@@ -17,6 +17,7 @@ pub fn target() -> TargetResult {
             cpu: "mips32r6".to_string(),
             features: "+mips32r6".to_string(),
             max_atomic_width: Some(32),
+            target_mcount: "_mcount".to_string(),
 
             ..super::linux_base::opts()
         },

src/librustc_target/spec/mipsisa64r6_unknown_linux_gnuabi64.rs

@@ -17,6 +17,7 @@ pub fn target() -> TargetResult {
             cpu: "mips64r6".to_string(),
             features: "+mips64r6".to_string(),
             max_atomic_width: Some(64),
+            target_mcount: "_mcount".to_string(),
 
             ..super::linux_base::opts()
         },

src/librustc_target/spec/mipsisa64r6el_unknown_linux_gnuabi64.rs

@@ -17,6 +17,7 @@ pub fn target() -> TargetResult {
             cpu: "mips64r6".to_string(),
             features: "+mips64r6".to_string(),
             max_atomic_width: Some(64),
+            target_mcount: "_mcount".to_string(),
 
             ..super::linux_base::opts()
         },

src/librustc_target/spec/mod.rs

@@ -761,7 +761,10 @@ pub struct TargetOptions {
     /// to opt out. The default is "aliases".
     ///
     /// Workaround for: https://github.com/rust-lang/rust/issues/57356
-    pub merge_functions: MergeFunctions
+    pub merge_functions: MergeFunctions,
+
+    /// Use platform dependent mcount function
+    pub target_mcount: String
 }
 
 impl Default for TargetOptions {
@@ -845,6 +848,7 @@ impl Default for TargetOptions {
             simd_types_indirect: true,
             override_export_symbols: None,
             merge_functions: MergeFunctions::Aliases,
+            target_mcount: "mcount".to_string(),
         }
     }
 }
@@ -1150,6 +1154,7 @@ impl Target {
         key!(simd_types_indirect, bool);
         key!(override_export_symbols, opt_list);
         key!(merge_functions, MergeFunctions)?;
+        key!(target_mcount);
 
         if let Some(array) = obj.find("abi-blacklist").and_then(Json::as_array) {
             for name in array.iter().filter_map(|abi| abi.as_string()) {
@@ -1364,6 +1369,7 @@ impl ToJson for Target {
         target_option_val!(simd_types_indirect);
         target_option_val!(override_export_symbols);
         target_option_val!(merge_functions);
+        target_option_val!(target_mcount);
 
         if default.abi_blacklist != self.options.abi_blacklist {
             d.insert("abi-blacklist".to_string(), self.options.abi_blacklist.iter()

src/librustc_target/spec/powerpc64_unknown_freebsd.rs

@@ -1,4 +1,4 @@
-use crate::spec::{LinkerFlavor, Target, TargetResult};
+use crate::spec::{LinkerFlavor, Target, TargetOptions, TargetResult};
 
 pub fn target() -> TargetResult {
     let mut base = super::freebsd_base::opts();
@@ -17,6 +17,9 @@ pub fn target() -> TargetResult {
         target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
-        options: base,
+        options: TargetOptions {
+            target_mcount: "_mcount".to_string(),
+            .. base
+        },
     })
 }

src/librustc_target/spec/powerpc64_unknown_linux_gnu.rs

@@ -1,4 +1,4 @@
-use crate::spec::{LinkerFlavor, Target, TargetResult, RelroLevel};
+use crate::spec::{LinkerFlavor, Target, TargetOptions, TargetResult, RelroLevel};
 
 pub fn target() -> TargetResult {
     let mut base = super::linux_base::opts();
@@ -21,6 +21,9 @@ pub fn target() -> TargetResult {
         target_env: "gnu".to_string(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
-        options: base,
+        options: TargetOptions {
+            target_mcount: "_mcount".to_string(),
+            .. base
+        },
     })
 }

src/librustc_target/spec/powerpc64_unknown_linux_musl.rs

@@ -1,4 +1,4 @@
-use crate::spec::{LinkerFlavor, Target, TargetResult};
+use crate::spec::{LinkerFlavor, Target, TargetOptions, TargetResult};
 
 pub fn target() -> TargetResult {
     let mut base = super::linux_musl_base::opts();
@@ -17,6 +17,9 @@ pub fn target() -> TargetResult {
         target_env: "musl".to_string(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
-        options: base,
+        options: TargetOptions {
+            target_mcount: "_mcount".to_string(),
+            .. base
+        },
     })
 }

src/librustc_target/spec/powerpc64le_unknown_linux_gnu.rs

@@ -1,4 +1,4 @@
-use crate::spec::{LinkerFlavor, Target, TargetResult};
+use crate::spec::{LinkerFlavor, Target, TargetOptions, TargetResult};
 
 pub fn target() -> TargetResult {
     let mut base = super::linux_base::opts();
@@ -17,6 +17,9 @@ pub fn target() -> TargetResult {
         target_env: "gnu".to_string(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
-        options: base,
+        options: TargetOptions {
+            target_mcount: "_mcount".to_string(),
+            .. base
+        },
     })
 }

src/librustc_target/spec/powerpc64le_unknown_linux_musl.rs

@@ -1,4 +1,4 @@
-use crate::spec::{LinkerFlavor, Target, TargetResult};
+use crate::spec::{LinkerFlavor, Target, TargetOptions, TargetResult};
 
 pub fn target() -> TargetResult {
     let mut base = super::linux_musl_base::opts();
@@ -17,6 +17,9 @@ pub fn target() -> TargetResult {
         target_env: "musl".to_string(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
-        options: base,
+        options: TargetOptions {
+            target_mcount: "_mcount".to_string(),
+            .. base
+        },
     })
 }

src/librustc_target/spec/powerpc_unknown_linux_gnu.rs

@@ -1,4 +1,4 @@
-use crate::spec::{LinkerFlavor, Target, TargetResult};
+use crate::spec::{LinkerFlavor, Target, TargetOptions, TargetResult};
 
 pub fn target() -> TargetResult {
     let mut base = super::linux_base::opts();
@@ -16,6 +16,9 @@ pub fn target() -> TargetResult {
         target_env: "gnu".to_string(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
-        options: base,
+        options: TargetOptions {
+            target_mcount: "_mcount".to_string(),
+            .. base
+        },
     })
 }

src/librustc_target/spec/powerpc_unknown_linux_gnuspe.rs

@@ -1,4 +1,4 @@
-use crate::spec::{LinkerFlavor, Target, TargetResult};
+use crate::spec::{LinkerFlavor, Target, TargetOptions, TargetResult};
 
 pub fn target() -> TargetResult {
     let mut base = super::linux_base::opts();
@@ -16,6 +16,9 @@ pub fn target() -> TargetResult {
         target_env: "gnu".to_string(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
-        options: base,
+        options: TargetOptions {
+            target_mcount: "_mcount".to_string(),
+            .. base
+        },
     })
 }

src/librustc_target/spec/powerpc_unknown_linux_musl.rs

@@ -1,4 +1,4 @@
-use crate::spec::{LinkerFlavor, Target, TargetResult};
+use crate::spec::{LinkerFlavor, Target, TargetOptions, TargetResult};
 
 pub fn target() -> TargetResult {
     let mut base = super::linux_musl_base::opts();
@@ -16,6 +16,9 @@ pub fn target() -> TargetResult {
         target_env: "musl".to_string(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
-        options: base,
+        options: TargetOptions {
+            target_mcount: "_mcount".to_string(),
+            .. base
+        },
     })
 }

src/librustc_target/spec/powerpc_unknown_netbsd.rs

@@ -1,4 +1,4 @@
-use crate::spec::{LinkerFlavor, Target, TargetResult};
+use crate::spec::{LinkerFlavor, Target, TargetOptions, TargetResult};
 
 pub fn target() -> TargetResult {
     let mut base = super::netbsd_base::opts();
@@ -16,6 +16,9 @@ pub fn target() -> TargetResult {
         target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
-        options: base,
+        options: TargetOptions {
+            target_mcount: "__mcount".to_string(),
+            .. base
+        },
     })
 }

src/librustc_target/spec/sparc64_unknown_netbsd.rs

@@ -1,4 +1,4 @@
-use crate::spec::{LinkerFlavor, Target, TargetResult};
+use crate::spec::{LinkerFlavor, Target, TargetOptions, TargetResult};
 
 pub fn target() -> TargetResult {
     let mut base = super::netbsd_base::opts();
@@ -17,6 +17,9 @@ pub fn target() -> TargetResult {
         target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
-        options: base,
+        options: TargetOptions {
+            target_mcount: "__mcount".to_string(),
+            .. base
+        },
     })
 }

src/librustc_target/spec/x86_64_apple_darwin.rs

@@ -1,4 +1,4 @@
-use crate::spec::{LinkerFlavor, Target, TargetResult};
+use crate::spec::{LinkerFlavor, Target, TargetOptions, TargetResult};
 
 pub fn target() -> TargetResult {
     let mut base = super::apple_base::opts();
@@ -19,6 +19,9 @@ pub fn target() -> TargetResult {
         target_env: String::new(),
         target_vendor: "apple".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
-        options: base,
+        options: TargetOptions {
+            target_mcount: "\u{1}mcount".to_string(),
+            .. base
+        },
     })
 }

src/librustc_target/spec/x86_64_rumprun_netbsd.rs

@@ -1,4 +1,4 @@
-use crate::spec::{LinkerFlavor, Target, TargetResult};
+use crate::spec::{LinkerFlavor, Target, TargetOptions, TargetResult};
 
 pub fn target() -> TargetResult {
     let mut base = super::netbsd_base::opts();
@@ -24,6 +24,9 @@ pub fn target() -> TargetResult {
         target_env: String::new(),
         target_vendor: "rumprun".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
-        options: base,
+        options: TargetOptions {
+            target_mcount: "__mcount".to_string(),
+            .. base
+        },
     })
 }

src/librustc_target/spec/x86_64_unknown_netbsd.rs

@@ -1,4 +1,4 @@
-use crate::spec::{LinkerFlavor, Target, TargetResult};
+use crate::spec::{LinkerFlavor, Target, TargetOptions, TargetResult};
 
 pub fn target() -> TargetResult {
     let mut base = super::netbsd_base::opts();
@@ -18,6 +18,9 @@ pub fn target() -> TargetResult {
         target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
-        options: base,
+        options: TargetOptions {
+            target_mcount: "__mcount".to_string(),
+            .. base
+        },
     })
 }

src/test/codegen/instrument-mcount.rs

@@ -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() {}