[ELF][MIPS] N32 ABI support

In short the patch introduces support for linking object file conform
MIPS N32 ABI [1]. This ABI is similar to N64 ABI but uses 32-bit
pointer size.

The most non-trivial requirement of this ABI is one more relocation
packing format. N64 ABI puts multiple relocation type into the single
relocation record. The N32 ABI uses series of successive relocations
with the same offset for this purpose. In this patch, new function
`mergeMipsN32RelTypes` handle this case and "convert" N32 relocation to
the N64 relocation so the rest of the code keep unchanged.

For now, linker does not support series of relocations applied to sections
without SHF_ALLOC bit. Probably later I will add the support or insert
some sort of assert into the `relocateNonAlloc` routine to catch this
case.

[1] ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/MIPS-N32-ABI-Handbook.pdf

Differential revision: https://reviews.llvm.org/D26298

1 files changed, 3 insertions, 0 deletions

diff --git a/lld/ELF/Writer.h b/lld/ELF/Writer.h
index b0d60b40077..3b6c6e52de2 100644
--- a/lld/ELF/Writer.h
+++ b/lld/ELF/Writer.h
@@ -16,6 +16,7 @@
 
 namespace lld {
 namespace elf {
+class InputFile;
 template <class ELFT> class OutputSectionBase;
 template <class ELFT> class InputSectionBase;
 template <class ELFT> class ObjectFile;
@@ -45,6 +46,8 @@ template <class ELFT> uint32_t getMipsEFlags();
 
 uint8_t getMipsFpAbiFlag(uint8_t OldFlag, uint8_t NewFlag,
                          llvm::StringRef FileName);
+
+bool isMipsN32Abi(const InputFile *F);
 }
 }