Replace the \01__gnu_mcount_nc to LLVM intrinsic for ARM

Current `-Zinstrument-mcount` for ARM32 use the `\01__gnu_mcount_nc`
directly for its instrumentation function.

However, the LLVM does not use this mcount function directly, but it wraps
it to intrinsic, `llvm.arm.gnu.eabi.mcount` and the transform pass also
only handle the intrinsic.

As a result, current `-Zinstrument-mcount` not work on ARM32.
Refer: namhyung/uftrace#1764

This commit replaces the mcount name from native function to the
LLVM intrinsic so that the transform pass can handle it.

Signed-off-by: ChoKyuWon <kyuwoncho18@gmail.com>

Author: ChoKyuWon

compiler/rustc_codegen_llvm/src/attributes.rs

@@ -128,7 +128,10 @@ fn instrument_function_attr<'ll>(cx: &CodegenCx<'ll, '_>) -> SmallVec<[&'ll Attr
 
         // The function name varies on platforms.
         // See test/CodeGen/mcount.c in clang.
-        let mcount_name = cx.sess().target.mcount.as_ref();
+        let mcount_name = match &cx.sess().target.llvm_mcount_intrinsic {
+            Some(llvm_mcount_intrinsic) => llvm_mcount_intrinsic.as_ref(),
+            None => cx.sess().target.mcount.as_ref(),
+        };
 
         attrs.push(llvm::CreateAttrStringValue(
             cx.llcx,

compiler/rustc_target/src/spec/arm_unknown_linux_gnueabi.rs

@@ -11,6 +11,7 @@ pub fn target() -> Target {
             features: "+strict-align,+v6".into(),
             max_atomic_width: Some(64),
             mcount: "\u{1}__gnu_mcount_nc".into(),
+            llvm_mcount_intrinsic: Some("llvm.arm.gnu.eabi.mcount".into()),
             ..super::linux_gnu_base::opts()
         },
     }

compiler/rustc_target/src/spec/arm_unknown_linux_gnueabihf.rs

@@ -11,6 +11,7 @@ pub fn target() -> Target {
             features: "+strict-align,+v6,+vfp2,-d32".into(),
             max_atomic_width: Some(64),
             mcount: "\u{1}__gnu_mcount_nc".into(),
+            llvm_mcount_intrinsic: Some("llvm.arm.gnu.eabi.mcount".into()),
             ..super::linux_gnu_base::opts()
         },
     }

compiler/rustc_target/src/spec/armeb_unknown_linux_gnueabi.rs

@@ -13,6 +13,7 @@ pub fn target() -> Target {
             endian: Endian::Big,
             max_atomic_width: Some(64),
             mcount: "\u{1}__gnu_mcount_nc".into(),
+            llvm_mcount_intrinsic: Some("llvm.arm.gnu.eabi.mcount".into()),
             ..super::linux_gnu_base::opts()
         },
     }

compiler/rustc_target/src/spec/armv4t_unknown_linux_gnueabi.rs

@@ -12,6 +12,7 @@ pub fn target() -> Target {
             // Atomic operations provided by compiler-builtins
             max_atomic_width: Some(32),
             mcount: "\u{1}__gnu_mcount_nc".into(),
+            llvm_mcount_intrinsic: Some("llvm.arm.gnu.eabi.mcount".into()),
             has_thumb_interworking: true,
             ..super::linux_gnu_base::opts()
         },

compiler/rustc_target/src/spec/armv6_unknown_freebsd.rs

@@ -13,6 +13,7 @@ pub fn target() -> Target {
             features: "+v6,+vfp2,-d32".into(),
             max_atomic_width: Some(64),
             mcount: "\u{1}__gnu_mcount_nc".into(),
+            llvm_mcount_intrinsic: Some("llvm.arm.gnu.eabi.mcount".into()),
             ..super::freebsd_base::opts()
         },
     }

compiler/rustc_target/src/spec/armv7_unknown_linux_gnueabi.rs

@@ -14,6 +14,7 @@ pub fn target() -> Target {
             features: "+v7,+thumb2,+soft-float,-neon".into(),
             max_atomic_width: Some(64),
             mcount: "\u{1}__gnu_mcount_nc".into(),
+            llvm_mcount_intrinsic: Some("llvm.arm.gnu.eabi.mcount".into()),
             ..super::linux_gnu_base::opts()
         },
     }

compiler/rustc_target/src/spec/mod.rs

@@ -1912,6 +1912,9 @@ pub struct TargetOptions {
     /// Use platform dependent mcount function
     pub mcount: StaticCow<str>,
 
+    /// Use LLVM intrinsic for mcount function name
+    pub llvm_mcount_intrinsic: Option<StaticCow<str>>,
+
     /// LLVM ABI name, corresponds to the '-mabi' parameter available in multilib C compilers
     pub llvm_abiname: StaticCow<str>,
 
@@ -2173,6 +2176,7 @@ impl Default for TargetOptions {
             override_export_symbols: None,
             merge_functions: MergeFunctions::Aliases,
             mcount: "mcount".into(),
+            llvm_mcount_intrinsic: None,
             llvm_abiname: "".into(),
             relax_elf_relocations: false,
             llvm_args: cvs![],
@@ -2829,6 +2833,7 @@ impl Target {
         key!(override_export_symbols, opt_list);
         key!(merge_functions, MergeFunctions)?;
         key!(mcount = "target-mcount");
+        key!(llvm_mcount_intrinsic, optional);
         key!(llvm_abiname);
         key!(relax_elf_relocations, bool);
         key!(llvm_args, list);
@@ -3085,6 +3090,7 @@ impl ToJson for Target {
         target_option_val!(override_export_symbols);
         target_option_val!(merge_functions);
         target_option_val!(mcount, "target-mcount");
+        target_option_val!(llvm_mcount_intrinsic);
         target_option_val!(llvm_abiname);
         target_option_val!(relax_elf_relocations);
         target_option_val!(llvm_args);