naked functions: respect function_sections on linux/macos

Author: folkertdev

compiler/rustc_codegen_ssa/src/mir/naked_asm.rs

@@ -203,8 +203,6 @@ fn prefix_and_suffix<'tcx>(
     let mut end = String::new();
     match asm_binary_format {
         BinaryFormat::Elf => {
-            let section = link_section.unwrap_or_else(|| format!(".text.{asm_name}"));
-
             let progbits = match is_arm {
                 true => "%progbits",
                 false => "@progbits",
@@ -215,7 +213,11 @@ fn prefix_and_suffix<'tcx>(
                 false => "@function",
             };
 
-            writeln!(begin, ".pushsection {section},\"ax\", {progbits}").unwrap();
+            if let Some(section) = &link_section {
+                writeln!(begin, ".pushsection {section},\"ax\", {progbits}").unwrap();
+            } else if function_sections {
+                writeln!(begin, ".pushsection .text.{asm_name},\"ax\", {progbits}").unwrap();
+            }
             writeln!(begin, ".balign {align_bytes}").unwrap();
             write_linkage(&mut begin).unwrap();
             match item_data.visibility {
@@ -234,14 +236,18 @@ fn prefix_and_suffix<'tcx>(
             // pattern match on assembly generated by LLVM.
             writeln!(end, ".Lfunc_end_{asm_name}:").unwrap();
             writeln!(end, ".size {asm_name}, . - {asm_name}").unwrap();
-            writeln!(end, ".popsection").unwrap();
+            if link_section.is_some() || function_sections {
+                writeln!(end, ".popsection").unwrap();
+            }
             if !arch_suffix.is_empty() {
                 writeln!(end, "{}", arch_suffix).unwrap();
             }
         }
         BinaryFormat::MachO => {
-            let section = link_section.unwrap_or_else(|| "__TEXT,__text".to_string());
-            writeln!(begin, ".pushsection {},regular,pure_instructions", section).unwrap();
+            // NOTE: LLVM ignores `-Zfunction-sections` on macos.
+            if let Some(section) = &link_section {
+                writeln!(begin, ".pushsection {section},regular,pure_instructions").unwrap();
+            }
             writeln!(begin, ".balign {align_bytes}").unwrap();
             write_linkage(&mut begin).unwrap();
             match item_data.visibility {
@@ -252,7 +258,9 @@ fn prefix_and_suffix<'tcx>(
 
             writeln!(end).unwrap();
             writeln!(end, ".Lfunc_end_{asm_name}:").unwrap();
-            writeln!(end, ".popsection").unwrap();
+            if link_section.is_some() || function_sections {
+                writeln!(end, ".popsection").unwrap();
+            }
             if !arch_suffix.is_empty() {
                 writeln!(end, "{}", arch_suffix).unwrap();
             }

tests/codegen-llvm/naked-fn/naked-functions.rs

@@ -24,7 +24,7 @@ use minicore::*;
 // linux,win: .intel_syntax
 //
 // linux:    .pushsection .text.naked_empty,\22ax\22, @progbits
-// macos:    .pushsection __TEXT,__text,regular,pure_instructions
+// macos-NOT: .pushsection
 // win_x86_msvc:     .pushsection .text$naked_empty,\22xr\22
 // win_x86_gnu-NOT:  .pushsection
 // win_i686_gnu-NOT: .pushsection
@@ -76,7 +76,7 @@ pub extern "C" fn naked_empty() {
 // linux,win: .intel_syntax
 //
 // linux:    .pushsection .text.naked_with_args_and_return,\22ax\22, @progbits
-// macos:    .pushsection __TEXT,__text,regular,pure_instructions
+// macos-NOT: .pushsection
 // win_x86_msvc:     .pushsection .text$naked_with_args_and_return,\22xr\22
 // win_x86_gnu-NOT:  .pushsection
 // win_i686_gnu-NOT: .pushsection