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 ↗

(On Diff #11615)

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 ↗

(On Diff #11615)

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).

llvm/trunk/lib/MC/MCObjectFileInfo.cpp

DwarfLocDWOSection =
     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::getMetadata());
+
 }
 
 
 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.

llvm/trunk/lib/Target/X86/X86AsmPrinter.cpp

if (!Stubs.empty()) {
 
       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);
 }