MachO: support custom section names on global variables

[t.p.northover]

Summary

These attributes have been accepted in ELF for a while, and are generated by Clang in some places, so it makes sense to support them on MachO too.

[Gerolf]

LGTM.

[t.p.northover]

Thanks, committed as 5c18444289.

llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp

report_fatal_error("MachO doesn't support COMDATs, '" + C->getName() +
                      "' cannot be lowered.");
 }
 
 MCSection *TargetLoweringObjectFileMachO::getExplicitSectionGlobal(
     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
 
   StringRef SectionName = GO->getSection();
 
+  const GlobalVariable *GV = dyn_cast<GlobalVariable>(GO);
+  if (GV && GV->hasImplicitSection()) {
+    auto Attrs = GV->getAttributes();
+    if (Attrs.hasAttribute("bss-section") && Kind.isBSS()) {
+      SectionName = Attrs.getAttribute("bss-section").getValueAsString();
+    } else if (Attrs.hasAttribute("rodata-section") && Kind.isReadOnly()) {
+      SectionName = Attrs.getAttribute("rodata-section").getValueAsString();
+    } else if (Attrs.hasAttribute("relro-section") && Kind.isReadOnlyWithRel()) {
+      SectionName = Attrs.getAttribute("relro-section").getValueAsString();
+    } else if (Attrs.hasAttribute("data-section") && Kind.isData()) {
+      SectionName = Attrs.getAttribute("data-section").getValueAsString();
+    }
+  }
+
   const Function *F = dyn_cast<Function>(GO);
   if (F && F->hasFnAttribute("implicit-section-name")) {
     SectionName = F->getFnAttribute("implicit-section-name").getValueAsString();
   }
 
   // Parse the section specifier and create it if valid.
   StringRef Segment, Section;
   unsigned TAA = 0, StubSize = 0;

llvm/test/CodeGen/AArch64/custom-sections.ll

+; RUN: llc -mtriple=arm64-apple-macosx %s -o - | FileCheck %s
+
+; CHECK-LABEL: .section __MY_DATA,__my_data
+; CHECK:       .globl _data
+; CHECK: _data:
+; CHECK:       .long 42
+@data = global i32 42 #0
+
+; CHECK-LABEL: .section __MY_BSS,__my_bss
+; CHECK:       .globl _bss
+; CHECK: _bss:
+; CHECK:       .long 0
+@bss = global i32 0 #0
+
+; CHECK-LABEL: .section __MY_RODATA,__my_rodata
+; CHECK:       .globl _const
+; CHECK: _const:
+; CHECK:       .long 42
+@const = constant i32 42 #0
+
+; CHECK-LABEL: .section __MY_RELRO,__my_relro
+; CHECK:       .globl _vars_relro
+; CHECK: _vars_relro:
+; CHECK:       .quad _data
+; CHECK:       .quad _bss
+@vars_relro = hidden constant [2 x ptr] [ptr @data, ptr @bss], align 16 #0
+
+attributes #0 = { "data-section"="__MY_DATA,__my_data" "bss-section"="__MY_BSS,__my_bss" "rodata-section"="__MY_RODATA,__my_rodata" "relro-section"="__MY_RELRO,__my_relro" }