move getDwarfExceptionSection from TAI to TLOF and rename it to

getLSDASection() to be more specific.  This makes it pretty obvious
that the ELF LSDA section is being specified wrong in PIC mode.  We're
probably getting a lot of startup-time relocations to a readonly page,
which is expensive and bad.

Someone who cares about ELF C++ should investigate this.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@77847 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Target/TargetAsmInfo.h

@@ -371,10 +371,6 @@ namespace llvm {
     ///
     const char *DwarfEHFrameSection; // Defaults to ".eh_frame".
     
-    /// DwarfExceptionSection - Section directive for Exception table.
-    ///
-    const char *DwarfExceptionSection; // Defaults to ".gcc_except_table".
-
     //===--- CBE Asm Translation Table -----------------------------------===//
 
     const char *const *AsmTransCBE; // Defaults to empty
@@ -637,9 +633,6 @@ namespace llvm {
     const char *getDwarfEHFrameSection() const {
       return DwarfEHFrameSection;
     }
-    const char *getDwarfExceptionSection() const {
-      return DwarfExceptionSection;
-    }
     const char *const *getAsmCBE() const {
       return AsmTransCBE;
     }

include/llvm/Target/TargetLoweringObjectFile.h

@@ -58,6 +58,10 @@ protected:
   /// list.
   const MCSection *StaticDtorSection;
   
+  /// LSDASection - If exception handling is supported by the target, this is
+  /// the section the Language Specific Data Area information is emitted to.
+  const MCSection *LSDASection;
+  
 public:
   // FIXME: NONPUB.
   const MCSection *getOrCreateSection(const char *Name,
@@ -77,10 +81,10 @@ public:
   
   const MCSection *getTextSection() const { return TextSection; }
   const MCSection *getDataSection() const { return DataSection; }
-
   const MCSection *getStaticCtorSection() const { return StaticCtorSection; }
   const MCSection *getStaticDtorSection() const { return StaticDtorSection; }
-
+  const MCSection *getLSDASection() const { return LSDASection; }
+  
   /// shouldEmitUsedDirectiveFor - This hook allows targets to selectively
   /// decide not to emit the UsedDirective for some symbols in llvm.used.
   /// FIXME: REMOVE this (rdar://7071300)

lib/CodeGen/AsmPrinter/DwarfException.cpp

@@ -20,10 +20,11 @@
 #include "llvm/Support/Timer.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Target/TargetAsmInfo.h"
-#include "llvm/Target/TargetRegisterInfo.h"
 #include "llvm/Target/TargetData.h"
 #include "llvm/Target/TargetFrameInfo.h"
+#include "llvm/Target/TargetLoweringObjectFile.h"
 #include "llvm/Target/TargetOptions.h"
+#include "llvm/Target/TargetRegisterInfo.h"
 #include "llvm/ADT/StringExtras.h"
 using namespace llvm;
 
@@ -539,10 +540,8 @@ void DwarfException::EmitExceptionTable() {
   unsigned SizeAlign = (4 - TotalSize) & 3;
 
   // Begin the exception table.
-  //MCSection *LSDASection = TAI->getLSDASection();
-  //Asm->SwitchToSection(LSDASection);
-  
-  Asm->SwitchToDataSection(TAI->getDwarfExceptionSection());
+  const MCSection *LSDASection = Asm->getObjFileLowering().getLSDASection();
+  Asm->SwitchToSection(LSDASection);
   Asm->EmitAlignment(2, 0, 0, false);
   O << "GCC_except_table" << SubprogramCount << ":\n";
 

lib/Target/PowerPC/PPCTargetAsmInfo.cpp

@@ -28,7 +28,6 @@ PPCDarwinTargetAsmInfo::PPCDarwinTargetAsmInfo(const PPCTargetMachine &TM) :
   
   DwarfEHFrameSection =
    ".section __TEXT,__eh_frame,coalesced,no_toc+strip_static_syms+live_support";
-  DwarfExceptionSection = ".section __DATA,__gcc_except_tab";
   GlobalEHDirective = "\t.globl\t";
   SupportsWeakOmittedEHFrame = false;
 }
@@ -73,7 +72,6 @@ PPCLinuxTargetAsmInfo::PPCLinuxTargetAsmInfo(const PPCTargetMachine &TM) :
     SupportsExceptionHandling = true;
   AbsoluteEHSectionOffsets = false;
   DwarfEHFrameSection = "\t.section\t.eh_frame,\"aw\",@progbits";
-  DwarfExceptionSection = "\t.section\t.gcc_except_table,\"a\",@progbits";
 }
 
 

lib/Target/TargetAsmInfo.cpp

@@ -108,7 +108,6 @@ TargetAsmInfo::TargetAsmInfo(const TargetMachine &tm) : TM(tm) {
   DwarfRangesSection = ".debug_ranges";
   DwarfMacroInfoSection = ".debug_macinfo";
   DwarfEHFrameSection = ".eh_frame";
-  DwarfExceptionSection = ".gcc_except_table";
   AsmTransCBE = 0;
 }
 

lib/Target/TargetLoweringObjectFile.cpp

@@ -36,6 +36,7 @@ TargetLoweringObjectFile::TargetLoweringObjectFile() : Ctx(0) {
   ReadOnlySection = 0;
   StaticCtorSection = 0;
   StaticDtorSection = 0;
+  LSDASection = 0;
 }
 
 TargetLoweringObjectFile::~TargetLoweringObjectFile() {
@@ -302,6 +303,14 @@ void TargetLoweringObjectFileELF::Initialize(MCContext &Ctx,
     getOrCreateSection(".ctors", false, SectionKind::getDataRel());
   StaticDtorSection =
     getOrCreateSection(".dtors", false, SectionKind::getDataRel());
+  
+  
+  // FIXME: We're emitting LSDA info into a readonly section on ELF, even though
+  // it contains relocatable pointers.  In PIC mode, this is probably a big
+  // runtime hit for C++ apps.  Either the contents of the LSDA need to be
+  // adjusted or this should be a data section.
+  LSDASection =
+    getOrCreateSection(".gcc_except_table", false, SectionKind::getReadOnly());
 }
 
 
@@ -537,6 +546,8 @@ void TargetLoweringObjectFileMachO::Initialize(MCContext &Ctx,
       getOrCreateSection(".mod_term_func", true, SectionKind::getDataRel());
   }
   
+  LSDASection = getOrCreateSection("__DATA,__gcc_except_tab", false,
+                                   SectionKind::getDataRel());
 }
 
 const MCSection *TargetLoweringObjectFileMachO::

lib/Target/X86/X86TargetAsmInfo.cpp

@@ -84,7 +84,6 @@ X86DarwinTargetAsmInfo::X86DarwinTargetAsmInfo(const X86TargetMachine &TM):
   AbsoluteEHSectionOffsets = false;
   DwarfEHFrameSection =
   ".section __TEXT,__eh_frame,coalesced,no_toc+strip_static_syms+live_support";
-  DwarfExceptionSection = ".section __DATA,__gcc_except_tab";
 }
 
 unsigned X86DarwinTargetAsmInfo::PreferredEHDataFormat() const {
@@ -133,7 +132,6 @@ X86ELFTargetAsmInfo::X86ELFTargetAsmInfo(const X86TargetMachine &TM) :
   SupportsExceptionHandling = true;
   AbsoluteEHSectionOffsets = false;
   DwarfEHFrameSection = "\t.section\t.eh_frame,\"aw\",@progbits";
-  DwarfExceptionSection = "\t.section\t.gcc_except_table,\"a\",@progbits";
 
   // On Linux we must declare when we can use a non-executable stack.
   if (TM.getSubtarget<X86Subtarget>().isLinux())