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Fix some fixme's in #if 0'd code by making it dependent on the structural

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behavior of the LSDA section instead of on some random target hook that
needs to be kept in synch with other points of truth.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@77855 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2009-08-02 03:59:56 +00:00
parent b9bcdd9ca4
commit ad88bc4076
1 changed files with 34 additions and 29 deletions
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63
lib/CodeGen/AsmPrinter/DwarfException.cpp
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@ -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");
}