From f4b92a8a00298a77ce78c19001651bdb79ab6aa6 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Fri, 31 Jul 2009 22:18:14 +0000
Subject: [PATCH] add some comments on how this is *supposed* to work.  We
 don't need the PreferredEHDataFormat hook, but I have yet-more refactoring to
 do before I can zap it.

llvm-svn: 77742
---
 .../lib/CodeGen/AsmPrinter/DwarfException.cpp | 27 +++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfException.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfException.cpp
index 0c710fc8130f..8eb97af0f942 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfException.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfException.cpp
@@ -539,6 +539,9 @@ void DwarfException::EmitExceptionTable() {
   unsigned SizeAlign = (4 - TotalSize) & 3;
 
   // Begin the exception table.
+  //MCSection *LSDASection = TAI->getLSDASection();
+  //Asm->SwitchToSection(LSDASection);
+  
   Asm->SwitchToDataSection(TAI->getDwarfExceptionSection());
   Asm->EmitAlignment(2, 0, 0, false);
   O << "GCC_except_table" << SubprogramCount << ":\n";
@@ -560,8 +563,32 @@ void DwarfException::EmitExceptionTable() {
     Asm->EmitInt8(dwarf::DW_EH_PE_omit);
     Asm->EOL("TType format (DW_EH_PE_omit)");
   } else {
+    // FIXME: Instead of using "PreferredEHDataFormat", we should use a simple
+    // approach to determine what needs to happen.  Basically, if the target
+    // wants the LSDA to be emitted into a read-only segment (like .text) then
+    // (unless in static mode) it can't output direct pointers to the typeinfo
+    // objects, which may be in an arbitrary locations.  Instead, it has to use
+    // and indirect stub pointer to get to the typeinfo.
+    //
+    // If the target wants to dump the LSDA's into a segment writable by the
+    // dynamic linker, then it can just use a normal pointer, and the dynamic
+    // linker will fix it up.
+    
+    // TODO: Replace the getDwarfExceptionSection() callback on TAI with a new
+    // getLSDASection() method on TLOF.  Merge and sanitize the implementations,
+    // and figure out what the ".gcc_except_table" directive expands to on elf
+    // systems.
+    
+    // 
+    //if (LSDASection->isWritable()) {
+    //Asm->EmitInt8(DW_EH_PE_absptr);
+    //} else {
+    //Asm->EmitInt8(DW_EH_PE_pcrel | DW_EH_PE_indirect | DW_EH_PE_sdata4);
+    //}
+    
     Asm->EmitInt8(TAI->PreferredEHDataFormat());
     
+    
     // FIXME: The comment here should correspond with what PreferredEHDataFormat
     // returned.
     Asm->EOL("TType format (DW_EH_PE_xxxxx)");