This adds a Darwin x86_64 relocation encoding for a subtraction expression

where both symbols are "local", that is non-external symbols, and there is
no "base" for the symbols used in the expression, that is the section has
no non-temporary symbols.  This case looks like this:

% cat local_reloc_A-B.s
	.long 0
LB:	.long 1
	.long LA - LB - 4
	.long 2
LA:	.long 3

which llvm-mc will not encode without this patch, generates a "unsupported
local relocations in difference" error, but the Darwin assembler will
encode with relocation entries like this:

% otool -rv a.out l.out 
a.out:
Relocation information (__TEXT,__text) 2 entries
address  pcrel length extern type    scattered symbolnum/value
00000008 False long   False  SUB     False     1 (__TEXT,__text)
00000008 False long   False  UNSIGND False     1 (__TEXT,__text)

which is very similar to what is encoded when the symbols don't have the
leading 'L' and they are not temporary symbols.  Which llvm-mc and the
Darwin assembler will encoded like this:

Relocation information (__TEXT,__text) 2 entries
address  pcrel length extern type    scattered symbolnum/value
00000008 False long   True   SUB     False     B
00000008 False long   True   UNSIGND False     A

This is the missing relocation encoding needed to allow the Mach-O x86
Dwarf file and line table to be emitted.  So this patch also removes the
TODO from the if() statement in MCMachOStreamer::Finish() that didn't 
call MCDwarfFileTable::Emit() for 64-bit targets.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@115389 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 1 insertions, 9 deletions

diff --git a/lib/MC/MCMachOStreamer.cpp b/lib/MC/MCMachOStreamer.cpp
index 42de0ae1b5..a10a63ee6a 100644
--- a/lib/MC/MCMachOStreamer.cpp
+++ b/lib/MC/MCMachOStreamer.cpp
@@ -441,15 +441,7 @@ void MCMachOStreamer::EmitInstruction(const MCInst &Inst) {
 
 void MCMachOStreamer::Finish() {
   // Dump out the dwarf file & directory tables and line tables.
-  if (getContext().hasDwarfFiles() &&
-      // TODO: This not enabled for 64-bit Mach-O targets.  As there are needed
-      // changes in the handling of 64-bit relocation entries for dwarf Mach-O
-      // sections that need to made.  Currently it gets
-      //   LLVM ERROR: unsupported local relocations in difference
-      // due dealing with "a-b" expressions made up for dwarf line entries
-      // because the line section has no non-local symbols thus it can't find
-      // an atom symbol for the base.
-      getAssembler().getBackend().getPointerSize() != 8) {
+  if (getContext().hasDwarfFiles()) {
     const MCSection *DwarfLineSection = getContext().getMachOSection("__DWARF",
                                          "__debug_line",
                                          MCSectionMachO::S_ATTR_DEBUG,