70bf5e514b
When the linker relaxes a GOT load, it changes ADRP+LDR instruction pair into ADRP+ADD. It is relatively straightforward to detect and symbolize the second instruction in the disassembler. However, it is not always possible to properly symbolize the ADRP instruction without looking at the second instruction. Hence, we have the FixRelaxationPass that adjust the operand of ADRP by looking at the corresponding ADD. This PR tries to properly symbolize ADRP earlier in the pipeline, i.e. in AArch64MCSymbolizer. This change makes it easier to adjust the instruction once we add AArch64 support in `scanExternalRefs()`. Additionally, we get a benefit of looking at proper operands while observing the function state prior to running FixRelaxationPass. To disambiguate the operand of ADRP that has a GOT relocation against it, we look at the contents/value of the operand. If it contains an address of a page that is valid for GOT, we assume that the operand wasn't modified by the linker and leave it up to FixRelaxationPass to do a proper adjustment. If the page referenced by ADRP cannot point to GOT, then it's an indication that the linker has modified the operand and we substitute the operand with a non-GOT reference to the symbol.
101 lines
2.3 KiB
ArmAsm
101 lines
2.3 KiB
ArmAsm
## Check that BOLT symbolizer properly handles loads from GOT, including
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## instruction sequences changed/relaxed by the linker.
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# RUN: split-file %s %t
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# RUN: llvm-mc -filetype=obj -triple aarch64-unknown-unknown %t/main.s \
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# RUN: -o %t/main.o
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# RUN: llvm-mc -filetype=obj -triple aarch64-unknown-unknown %t/near.s \
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# RUN: -o %t/near.o
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# RUN: llvm-mc -filetype=obj -triple aarch64-unknown-unknown %t/far.s \
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# RUN: -o %t/far.o
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# RUN: %clang %cflags %t/main.o %t/near.o %t/far.o -o %t/main.exe -Wl,-q -static
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# RUN: llvm-bolt %t/main.exe -o %t/main.bolt --keep-nops --print-disasm \
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# RUN: --print-only=_start | FileCheck %s
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#--- main.s
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.text
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.globl _start
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.p2align 2
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.type _start, @function
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# CHECK-LABEL: _start
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_start:
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## Function address load relaxable into nop+adr.
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# CHECK: nop
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# CHECK-NEXT: adr x0, near
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adrp x0, :got:near
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ldr x0, [x0, :got_lo12:near]
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## Function address load relaxable into adrp+add.
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# CHECK-NEXT: adrp x1, far
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# CHECK-NEXT: add x1, x1, :lo12:far
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adrp x1, :got:far
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ldr x1, [x1, :got_lo12:far]
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## Non-relaxable due to the instruction in-between.
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# CHECK-NEXT: adrp x2, __BOLT_got_zero
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# CHECK-NEXT: nop
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# CHECK-NEXT: ldr x2, [x2, :lo12:__BOLT_got_zero{{.*}}]
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adrp x2, :got:near
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nop
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ldr x2, [x2, :got_lo12:near]
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## Load data object with local visibility. Relaxable into adrp+add.
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# CHECK-NEXT: adrp x3, "local_far_data/1"
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# CHECK-NEXT: add x3, x3, :lo12:"local_far_data/1"
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adrp x3, :got:local_far_data
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ldr x3, [x3, :got_lo12:local_far_data]
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## Global data reference relaxable into adrp+add.
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# CHECK-NEXT: adrp x4, far_data
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# CHECK-NEXT: add x4, x4, :lo12:far_data
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adrp x4, :got:far_data
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ldr x4, [x4, :got_lo12:far_data]
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ret
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.size _start, .-_start
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.weak near
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.weak far
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.weak far_data
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## Data object separated by more than 1MB from _start.
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.data
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.type local_far_data, @object
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local_far_data:
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.xword 0
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.size local_far_data, .-local_far_data
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#--- near.s
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.text
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.globl near
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.type near, @function
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near:
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ret
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.size near, .-near
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#--- far.s
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.text
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## Insert 1MB of empty space to make objects after it unreachable by adr
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## instructions in _start.
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.space 0x100000
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.globl far
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.type far, @function
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far:
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ret
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.size far, .-far
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.data
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.globl far_data
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.type far_data, @object
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far_data:
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.xword 0
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.size far_data, .-far_data
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