[PATCH] D35242: [ARM, ELF] Don't shift movt relocation offsets
Rafael Avila de Espindola via llvm-commits
llvm-commits at lists.llvm.org
Tue Jul 11 08:49:15 PDT 2017
LGTM.
This will allow a pretty massive cleanup, but that is probably better
done as a follow up patch.
Thanks!
Martin Storsjö via Phabricator via llvm-commits
<llvm-commits at lists.llvm.org> writes:
> mstorsjo created this revision.
> Herald added subscribers: kristof.beyls, javed.absar, aemerson.
>
> 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.
>
>
> https://reviews.llvm.org/D35242
>
> Files:
> lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
> test/MC/ARM/elf-movt.s
>
>
> Index: test/MC/ARM/elf-movt.s
> ===================================================================
> --- test/MC/ARM/elf-movt.s
> +++ test/MC/ARM/elf-movt.s
> @@ -14,19 +14,31 @@
> 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:
> @OBJ-NEXT: 0: f0 0f 0f e3 movw r0, #65520
> @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
> + at OBJ-NEXT: 8: d2 04 00 e3 movw r0, #1234
> + at OBJ-NEXT: 00000008: R_ARM_MOVW_ABS_NC extern_symbol
> + at OBJ-NEXT: c: d2 04 40 e3 movt r0, #1234
> + at OBJ-NEXT: 0000000c: R_ARM_MOVT_ABS extern_symbol
>
> @THUMB: Disassembly of section .text:
> @THUMB-NEXT: barf:
> @THUMB-NEXT: 0: 4f f6 f0 70 movw r0, #65520
> @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
> + at THUMB-NEXT: 8: 40 f2 d2 40 movw r0, #1234
> + at THUMB-NEXT: 00000008: R_ARM_THM_MOVW_ABS_NC extern_symbol
> + at THUMB-NEXT: c: c0 f2 d2 40 movt r0, #1234
> + at THUMB-NEXT: 0000000c: R_ARM_THM_MOVT_ABS extern_symbol
> Index: lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
> ===================================================================
> --- lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
> +++ lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
> @@ -392,7 +392,7 @@
> 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 @@
> 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: {
>
>
> Index: test/MC/ARM/elf-movt.s
> ===================================================================
> --- test/MC/ARM/elf-movt.s
> +++ test/MC/ARM/elf-movt.s
> @@ -14,19 +14,31 @@
> 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:
> @OBJ-NEXT: 0: f0 0f 0f e3 movw r0, #65520
> @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
> + at OBJ-NEXT: 8: d2 04 00 e3 movw r0, #1234
> + at OBJ-NEXT: 00000008: R_ARM_MOVW_ABS_NC extern_symbol
> + at OBJ-NEXT: c: d2 04 40 e3 movt r0, #1234
> + at OBJ-NEXT: 0000000c: R_ARM_MOVT_ABS extern_symbol
>
> @THUMB: Disassembly of section .text:
> @THUMB-NEXT: barf:
> @THUMB-NEXT: 0: 4f f6 f0 70 movw r0, #65520
> @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
> + at THUMB-NEXT: 8: 40 f2 d2 40 movw r0, #1234
> + at THUMB-NEXT: 00000008: R_ARM_THM_MOVW_ABS_NC extern_symbol
> + at THUMB-NEXT: c: c0 f2 d2 40 movt r0, #1234
> + at THUMB-NEXT: 0000000c: R_ARM_THM_MOVT_ABS extern_symbol
> Index: lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
> ===================================================================
> --- lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
> +++ lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
> @@ -392,7 +392,7 @@
> 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 @@
> 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: {
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