Emit .eh_frame with relocations to functions, rather than sections

When LLVM emits DWARF call frame information, it currently creates a local,
section-relative symbol in the code section, which is pointed to by a
relocation on the .eh_frame section. However, for C++ we emit some functions in
section groups, and the SysV ABI has some rules to make it easier to remove
these sections
(http://www.sco.com/developers/gabi/latest/ch4.sheader.html#section_group_rules):

  A symbol table entry with STB_LOCAL binding that is defined relative to one
  of a group's sections, and that is contained in a symbol table section that is
  not part of the group, must be discarded if the group members are discarded.
  References to this symbol table entry from outside the group are not allowed.

This means that we need to use the function symbol for the relocation, not a
temporary symbol.

There was a comment in the code claiming that the local symbol was used to
avoid creating a relocation, but a relocation must be created anyway as the
code and CFI are in different sections.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221150 91177308-0d34-0410-b5e6-96231b3b80d8

lib/MC/MCObjectStreamer.cpp

@@ -128,10 +128,13 @@ void MCObjectStreamer::EmitValueImpl(const MCExpr *Value, unsigned Size,
   DF->getContents().resize(DF->getContents().size() + Size, 0);
 }
 
-void MCObjectStreamer::EmitCFIStartProcImpl(MCDwarfFrameInfo &Frame) {
-  // We need to create a local symbol to avoid relocations.
-  Frame.Begin = getContext().CreateTempSymbol();
-  EmitLabel(Frame.Begin);
+void MCObjectStreamer::EmitCFIStartProcImpl(MCDwarfFrameInfo &Frame,
+                                            MCSymbol *FuncSym) {
+  if (!FuncSym) {
+    FuncSym = getContext().CreateTempSymbol();
+    EmitLabel(FuncSym);
+  }
+  Frame.Begin = FuncSym;
 }
 
 void MCObjectStreamer::EmitCFIEndProcImpl(MCDwarfFrameInfo &Frame) {