add support for powerpc/powerpc64 unaligned relocations

R_PPC_UADDR32 (R_PPC64_UADDR64) has the same meaning as R_PPC_ADDR32
(R_PPC64_ADDR64), except that its address need not be aligned. For
powerpc64, BFD ld(1) will automatically convert between ADDR<->UADDR
relocations when the address is/isn't at its native alignment. This
will happen if, for example, there is a pointer in a packed struct.

gold and lld do not currently generate R_PPC64_UADDR64, but pass
through misaligned R_PPC64_ADDR64 relocations from object files,
possibly relaxing them to misaligned R_PPC64_RELATIVE. In both cases
(relaxed or not) this violates the PSABI, which defines the relevant
field type as "a 64-bit field occupying 8 bytes, the alignment of
which is 8 bytes unless otherwise specified."

All three linkers violate the PSABI on 32-bit powerpc, where the only
difference is that the field is 32 bits wide, aligned to 4 bytes.

Currently musl fails to load executables linked by BFD ld containing
R_PPC64_UADDR64, with the error "unsupported relocation type 43".
This change provides compatibility with BFD ld on powerpc64, and any
static linker on either architecture that starts following the PSABI
more closely.

1 files changed, 1 insertions, 0 deletions

diff --git a/arch/powerpc64/reloc.h b/arch/powerpc64/reloc.h
index faf70acd..5bdaeede 100644
--- a/arch/powerpc64/reloc.h
+++ b/arch/powerpc64/reloc.h
@@ -11,6 +11,7 @@
 #define TPOFF_K (-0x7000)
 
 #define REL_SYMBOLIC    R_PPC64_ADDR64
+#define REL_USYMBOLIC   R_PPC64_UADDR64
 #define REL_GOT         R_PPC64_GLOB_DAT
 #define REL_PLT         R_PPC64_JMP_SLOT
 #define REL_RELATIVE    R_PPC64_RELATIVE