[XRay][CodeGen] Use the current function symbol as the associated symbol for the instrumentation map

Summary:
XRay had been assuming that the previous section is the "text" section
of the function when lowering the instrumentation map. Unfortunately
this is not a safe assumption, because we may be coming from lowering
debug type information for the function being lowered.

This fixes an issue with combining -gsplit-dwarf, -generate-type-units,
-debug-compile and -fxray-instrument for sole member functions. When the
split dwarf section is stripped, we're left with references from the
xray_instr_map to the debug section. The change now uses the function's
symbol instead of the previous section's start symbol.

We found the bug while attempting to strip the split debug sections off
an XRay-instrumented object file, which had a peculiar edge-case for
single-function classes where the single function is being lowered.
Because XRay had assocaited the instrumentation map for a function to
the debug types section instead of the function's section, the objcopy
call will fail due to the misplaced reference from the xray_instr_map
section.

Reviewers: pcc, dblaikie, echristo

Subscribers: llvm-commits, aprantl

Differential Revision: https://reviews.llvm.org/D37791

llvm-svn: 313233

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index 87399354945..ee5cb35fa9d 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -2785,7 +2785,7 @@ void AsmPrinter::emitXRayTable() {
   MCSection *InstMap = nullptr;
   MCSection *FnSledIndex = nullptr;
   if (MF->getSubtarget().getTargetTriple().isOSBinFormatELF()) {
-    auto Associated = dyn_cast<MCSymbolELF>(PrevSection->getBeginSymbol());
+    auto Associated = dyn_cast<MCSymbolELF>(CurrentFnSym);
     assert(Associated != nullptr);
     auto Flags = ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_LINK_ORDER;
     std::string GroupName;