diff options
Diffstat (limited to 'lib/CodeGen/AsmPrinter/DwarfException.cpp')
| -rw-r--r-- | lib/CodeGen/AsmPrinter/DwarfException.cpp | 63 |
1 files changed, 34 insertions, 29 deletions
diff --git a/lib/CodeGen/AsmPrinter/DwarfException.cpp b/lib/CodeGen/AsmPrinter/DwarfException.cpp index b051f7138e..aa52d87f27 100644 --- a/lib/CodeGen/AsmPrinter/DwarfException.cpp +++ b/lib/CodeGen/AsmPrinter/DwarfException.cpp @@ -557,40 +557,45 @@ void DwarfException::EmitExceptionTable() { Asm->EOL("LPStart format (DW_EH_PE_omit)"); #if 0 - // FIXME: This should default to what the system wants, not just "absptr". if (TypeInfos.empty() && FilterIds.empty()) { + // If there are no typeinfos or filters, there is nothing to emit, optimize + // by specifying the "omit" encoding. 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. + // Okay, we have actual filters or typeinfos to emit. As such, we need to + // pick a type encoding for them. We're about to emit a list of pointers to + // typeinfo objects at the end of the LSDA. However, unless we're in static + // mode, this reference will require a relocation by the dynamic linker. // - // 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)"); + // Because of this, we have a couple of options: + // 1) If we are in -static mode, we can always use an absolute reference + // from the LSDA, because the static linker will resolve it. + // 2) Otherwise, if the LSDA section is writable, we can output the direct + // reference to the typeinfo and allow the dynamic linker to relocate + // it. Since it is in a writable section, the dynamic linker won't + // have a problem. + // 3) Finally, if we're in PIC mode and the LDSA section isn't writable, + // we need to use some form of indirection. For example, on Darwin, + // we can output a statically-relocatable reference to a dyld stub. The + // offset to the stub is constant, but the contents are in a section + // that is updated by the dynamic linker. This is easy enough, but we + // need to tell the personality function of the unwinder to indirect + // through the dyld stub. + // + // FIXME: When this is actually implemented, we'll have to emit the stubs + // somewhere. This predicate should be moved to a shared location that is + // in target-independent code. + // + if (LSDASection->isWritable() || + Asm->TM.getRelocationModel() == Reloc::Static) { + Asm->EmitInt8(DW_EH_PE_absptr); + Asm->EOL("TType format (DW_EH_PE_absptr)"); + } else { + Asm->EmitInt8(DW_EH_PE_pcrel | DW_EH_PE_indirect | DW_EH_PE_sdata4); + Asm->EOL("TType format (DW_EH_PE_pcrel | DW_EH_PE_indirect" + " | DW_EH_PE_sdata4)"); + } Asm->EmitULEB128Bytes(TypeOffset); Asm->EOL("TType base offset"); } |