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
diff --git a/lib/MC/MachObjectWriter.cpp b/lib/MC/MachObjectWriter.cpp
index 689aabc..4bb0535 100644
--- a/lib/MC/MachObjectWriter.cpp
+++ b/lib/MC/MachObjectWriter.cpp
@@ -616,22 +616,32 @@
if (IsPCRel)
report_fatal_error("unsupported pc-relative relocation of difference");
- // We don't currently support any situation where one or both of the
- // symbols would require a local relocation. This is almost certainly
- // unused and may not be possible to encode correctly.
- if (!A_Base || !B_Base)
- report_fatal_error("unsupported local relocations in difference");
+ // The support for the situation where one or both of the symbols would
+ // require a local relocation is handled just like if the symbols were
+ // external. This is certainly used in the case of debug sections where
+ // the section has only temporary symbols and thus the symbols don't have
+ // base symbols. This is encoded using the section ordinal and
+ // non-extern relocation entries.
// Darwin 'as' doesn't emit correct relocations for this (it ends up with
- // a single SIGNED relocation); reject it for now.
- if (A_Base == B_Base)
+ // a single SIGNED relocation); reject it for now. Except the case where
+ // both symbols don't have a base, equal but both NULL.
+ if (A_Base == B_Base && A_Base)
report_fatal_error("unsupported relocation with identical base");
- Value += Layout.getSymbolAddress(&A_SD) - Layout.getSymbolAddress(A_Base);
- Value -= Layout.getSymbolAddress(&B_SD) - Layout.getSymbolAddress(B_Base);
+ Value += Layout.getSymbolAddress(&A_SD) -
+ (A_Base == NULL ? 0 : Layout.getSymbolAddress(A_Base));
+ Value -= Layout.getSymbolAddress(&B_SD) -
+ (B_Base == NULL ? 0 : Layout.getSymbolAddress(B_Base));
- Index = A_Base->getIndex();
- IsExtern = 1;
+ if (A_Base) {
+ Index = A_Base->getIndex();
+ IsExtern = 1;
+ }
+ else {
+ Index = A_SD.getFragment()->getParent()->getOrdinal() + 1;
+ IsExtern = 0;
+ }
Type = RIT_X86_64_Unsigned;
MachRelocationEntry MRE;
@@ -643,8 +653,14 @@
(Type << 28));
Relocations[Fragment->getParent()].push_back(MRE);
- Index = B_Base->getIndex();
- IsExtern = 1;
+ if (B_Base) {
+ Index = B_Base->getIndex();
+ IsExtern = 1;
+ }
+ else {
+ Index = B_SD.getFragment()->getParent()->getOrdinal() + 1;
+ IsExtern = 0;
+ }
Type = RIT_X86_64_Subtractor;
} else {
const MCSymbol *Symbol = &Target.getSymA()->getSymbol();