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[ARM, ELF] Don't shift movt relocation offsets 

For ELF, a movw+movt pair is handled as two separate relocations.
If an offset should be applied to the symbol address, this offset is
stored as an immediate in the instruction (as opposed to stored as an
offset in the relocation itself).

Even though the actual value stored in the movt immediate after linking
is the top half of the value, we need to store the unshifted offset
prior to linking. When the relocation is made during linking, the offset
gets added to the target symbol value, and the upper half of the value
is stored in the instruction.

This makes sure that movw+movt with offset symbols get properly
handled, in case the offset addition in the lower half should be
carried over to the upper half.

This makes the output from the additions to the test case match
the output from GNU binutils.

For COFF and MachO, the movw/movt relocations are handled as a pair,
and the overflow from the lower half gets carried over to the movt,
so they should keep the shifted offset just as before.

Differential Revision: https://reviews.llvm.org/D35242

llvm-svn: 307713
This commit is contained in:
Martin Storsjo 2017-07-11 21:07:10 +00:00
parent 95c003b96f
commit 0e83e85f63
2 changed files with 14 additions and 2 deletions
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4
llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
View File

@ -392,7 +392,7 @@ unsigned ARMAsmBackend::adjustFixupValue(const MCAssembler &Asm,
case FK_SecRel_4:
return Value;
case ARM::fixup_arm_movt_hi16:
if (!IsPCRel)
if (!IsPCRel && !STI->getTargetTriple().isOSBinFormatELF())
Value >>= 16;
LLVM_FALLTHROUGH;
case ARM::fixup_arm_movw_lo16: {
@ -404,7 +404,7 @@ unsigned ARMAsmBackend::adjustFixupValue(const MCAssembler &Asm,
return Value;
}
case ARM::fixup_t2_movt_hi16:
if (!IsPCRel)
if (!IsPCRel && !STI->getTargetTriple().isOSBinFormatELF())
Value >>= 16;
LLVM_FALLTHROUGH;
case ARM::fixup_t2_movw_lo16: {

12
llvm/test/MC/ARM/elf-movt.s
View File

@ -14,8 +14,12 @@ barf: @ @barf
movw r0, :lower16:GOT-(.LPC0_2+8)
movt r0, :upper16:GOT-(.LPC0_2+8)
.LPC0_2:
movw r0, :lower16:extern_symbol+1234
movt r0, :upper16:extern_symbol+1234
@ ASM: movw r0, :lower16:(GOT-(.LPC0_2+8))
@ ASM-NEXT: movt r0, :upper16:(GOT-(.LPC0_2+8))
@ ASM: movw r0, :lower16:(extern_symbol+1234)
@ ASM-NEXT: movt r0, :upper16:(extern_symbol+1234)
@OBJ: Disassembly of section .text:
@OBJ-NEXT: barf:
@ -23,6 +27,10 @@ barf: @ @barf
@OBJ-NEXT: 00000000: R_ARM_MOVW_PREL_NC GOT
@OBJ-NEXT: 4: f4 0f 4f e3 movt r0, #65524
@OBJ-NEXT: 00000004: R_ARM_MOVT_PREL GOT
@OBJ-NEXT: 8: d2 04 00 e3 movw r0, #1234
@OBJ-NEXT: 00000008: R_ARM_MOVW_ABS_NC extern_symbol
@OBJ-NEXT: c: d2 04 40 e3 movt r0, #1234
@OBJ-NEXT: 0000000c: R_ARM_MOVT_ABS extern_symbol
@THUMB: Disassembly of section .text:
@THUMB-NEXT: barf:
@ -30,3 +38,7 @@ barf: @ @barf
@THUMB-NEXT: 00000000: R_ARM_THM_MOVW_PREL_NC GOT
@THUMB-NEXT: 4: cf f6 f4 70 movt r0, #65524
@THUMB-NEXT: 00000004: R_ARM_THM_MOVT_PREL GOT
@THUMB-NEXT: 8: 40 f2 d2 40 movw r0, #1234
@THUMB-NEXT: 00000008: R_ARM_THM_MOVW_ABS_NC extern_symbol
@THUMB-NEXT: c: c0 f2 d2 40 movt r0, #1234
@THUMB-NEXT: 0000000c: R_ARM_THM_MOVT_ABS extern_symbol