Add support for StackMap section for ELF/Linux systems

[reames]

Summary

This patch emits the StackMap section on ELF systems. This is required to support llvm.experimental.stackmap and llvm.experimental.patchpoint.

Careful review is appreciated. I don't know the areas I'm touching well and may have gotten things wrong. A couple of things for specific review:

• Are the flags to getELFSection correct?
• Should I change the name of label following the section start?

Worth noting is that previous versions of this patch have been proposed but not submitted several times. For example, one was proposed here:
http://comments.gmane.org/gmane.comp.compilers.llvm.cvs/171038

The code in this change set is original.

[ributzka]

lib/MC/MCObjectFileInfo.cpp

590

I am not familiar with the ELF sections, but wouldn't Metadata be a better for for this section. I guess it doesn't work with it, because the JIT won't ask the client to allocate it?

Lang knows more about this part of the JIT.

[reames]

lib/MC/MCObjectFileInfo.cpp

590

Worth noting:

1. The COFF section uses getMetadata
2. getMetadata appears to work in practice

I'm happy to make the change, but don't feel like I understand the implications. Reading through the documentation, I'm unclear on the semantics. Lang, can you clarify?

[reames]

Switching the section type to be metadata instead of readonly based on review comments.

[ributzka]

LGTM

[echristo]

Yes, LGTM too. Sorry I missed this.

-eric

[reames]

Closed by commit rL214538 (authored by @reames).

lib/MC/MCObjectFileInfo.cpp

     Ctx->getELFSection(".debug_loc.dwo", ELF::SHT_PROGBITS, 0,
                        SectionKind::getMetadata());
   DwarfStrOffDWOSection =
     Ctx->getELFSection(".debug_str_offsets.dwo", ELF::SHT_PROGBITS, 0,
                        SectionKind::getMetadata());
   DwarfAddrSection =
     Ctx->getELFSection(".debug_addr", ELF::SHT_PROGBITS, 0,
                        SectionKind::getMetadata());
+
+  StackMapSection =
+    Ctx->getELFSection(".llvm_stackmaps", ELF::SHT_PROGBITS,
+                       ELF::SHF_ALLOC,
+                       SectionKind::getReadOnly());
+
 }
 
 
 void MCObjectFileInfo::InitCOFFMCObjectFileInfo(Triple T) {
   bool IsWoA = T.getArch() == Triple::arm || T.getArch() == Triple::thumb;
 
   // The object file format cannot represent common symbols with explicit
   // alignments.

lib/Target/X86/X86AsmPrinter.cpp

 
       for (const auto &Stub : Stubs) {
         OutStreamer.EmitLabel(Stub.first);
         OutStreamer.EmitSymbolValue(Stub.second.getPointer(),
                                     TD->getPointerSize());
       }
       Stubs.clear();
     }
+
+    SM.serializeToStackMapSection();
   }
 }
 
 //===----------------------------------------------------------------------===//
 // Target Registry Stuff
 //===----------------------------------------------------------------------===//
 
 // Force static initialization.
 extern "C" void LLVMInitializeX86AsmPrinter() {
   RegisterAsmPrinter<X86AsmPrinter> X(TheX86_32Target);
   RegisterAsmPrinter<X86AsmPrinter> Y(TheX86_64Target);
 }

test/CodeGen/X86/stackmap-elf.ll

+; RUN: llc < %s -mtriple=x86_64-linux-generic -disable-fp-elim | FileCheck %s
+; 
+; Note: This test file should cover only ELF specific formatting. 
+; Generic stackmap tests should go in the macho test files.
+;
+; Note: Print verbose stackmaps using -debug-only=stackmaps.
+
+; CHECK-LABEL:  .section  .llvm_stackmaps,"a",@progbits
+; CHECK-NEXT:  __LLVM_StackMaps:
+; Header
+; CHECK-NEXT:   .byte 1
+; CHECK-NEXT:   .byte 0
+; CHECK-NEXT:   .short 0
+; Num Functions
+; CHECK-NEXT:   .long 1
+; Num LargeConstants
+; CHECK-NEXT:   .long 0
+; Num Callsites
+; CHECK-NEXT:   .long 1
+
+; Functions and stack size
+; CHECK-NEXT:   .quad stackmap_elf
+; CHECK-NEXT:   .quad 8
+
+; Callsites
+; Constant arguments
+;
+; CHECK-NEXT:   .quad   1
+; CHECK-NEXT:   .long   .Ltmp{{.*}}-stackmap_elf
+; CHECK-NEXT:   .short  0
+; CHECK-NEXT:   .short  1
+; SmallConstant
+; CHECK-NEXT:   .byte   4
+; CHECK-NEXT:   .byte   8
+; CHECK-NEXT:   .short  0
+; CHECK-NEXT:   .long   155
+define void @stackmap_elf() {
+entry:
+  %0 = inttoptr i64 12345000 to i8*
+  tail call void (i64, i32, ...)* @llvm.experimental.stackmap(i64 1, i32 15, i32 155)
+  ret void
+}
+
+declare void @llvm.experimental.stackmap(i64, i32, ...)