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.

llvm-svn: 221150

1 files changed, 9 insertions, 2 deletions

diff --git a/llvm/lib/MC/MCParser/AsmParser.cpp b/llvm/lib/MC/MCParser/AsmParser.cpp
index de7d96129f1..5a56094a3c7 100644
--- a/llvm/lib/MC/MCParser/AsmParser.cpp
+++ b/llvm/lib/MC/MCParser/AsmParser.cpp
@@ -172,6 +172,9 @@ private:
   /// \brief Are we parsing ms-style inline assembly?
   bool ParsingInlineAsm;
 
+  /// \brief The last symbol we emitted, used for call frame information.
+  MCSymbol *LastFuncSymbol;
+
 public:
   AsmParser(SourceMgr &SM, MCContext &Ctx, MCStreamer &Out,
             const MCAsmInfo &MAI);
@@ -491,7 +494,8 @@ AsmParser::AsmParser(SourceMgr &_SM, MCContext &_Ctx, MCStreamer &_Out,
     : Lexer(_MAI), Ctx(_Ctx), Out(_Out), MAI(_MAI), SrcMgr(_SM),
       PlatformParser(nullptr), CurBuffer(_SM.getMainFileID()),
       MacrosEnabledFlag(true), HadError(false), CppHashLineNumber(0),
-      AssemblerDialect(~0U), IsDarwin(false), ParsingInlineAsm(false) {
+      AssemblerDialect(~0U), IsDarwin(false), ParsingInlineAsm(false),
+      LastFuncSymbol(nullptr) {
   // Save the old handler.
   SavedDiagHandler = SrcMgr.getDiagHandler();
   SavedDiagContext = SrcMgr.getDiagContext();
@@ -1305,6 +1309,9 @@ bool AsmParser::parseStatement(ParseStatementInfo &Info,
     if (!ParsingInlineAsm)
       Out.EmitLabel(Sym);
 
+    // Record the symbol, so that it can be used for call frame information
+    LastFuncSymbol = Sym;
+
     // If we are generating dwarf for assembly source files then gather the
     // info to make a dwarf label entry for this label if needed.
     if (getContext().getGenDwarfForAssembly())
@@ -2961,7 +2968,7 @@ bool AsmParser::parseDirectiveCFIStartProc() {
     if (parseIdentifier(Simple) || Simple != "simple")
       return TokError("unexpected token in .cfi_startproc directive");
 
-  getStreamer().EmitCFIStartProc(!Simple.empty());
+  getStreamer().EmitCFIStartProc(!Simple.empty(), LastFuncSymbol);
   return false;
 }