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[BOLT][AArch64] Handle .plt.got section (#71216)
It seems that currently this section is only created by the mold linker if 2 conditions are met: 1. The PLT function was called directly. 2. The indirect access to PLT function was found (e.g. through ADRP relocation). Although mold created symbol for every plt entry I've removed them in yaml file to check that .plt.got was truly disassembled by bolt.
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4 files changed

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lines changed

4 files changed

+234
-3
lines changed

‎bolt/include/bolt/Rewrite/RewriteInstance.h‎

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -509,11 +509,11 @@ class RewriteInstance {
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};
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/// AArch64 PLT sections.
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const PLTSectionInfo AArch64_PLTSections[3] = {
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{".plt"}, {".iplt"}, {nullptr}};
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const PLTSectionInfo AArch64_PLTSections[4] = {
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{".plt"}, {".plt.got"}, {".iplt"}, {nullptr}};
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/// RISCV PLT sections.
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const PLTSectionInfo RISCV_PLTSections[3] = {{".plt"}, {nullptr}};
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const PLTSectionInfo RISCV_PLTSections[2] = {{".plt"}, {nullptr}};
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/// Return PLT information for a section with \p SectionName or nullptr
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/// if the section is not PLT.

‎bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp‎

Lines changed: 8 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -862,6 +862,14 @@ class AArch64MCPlusBuilder : public MCPlusBuilder {
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/// add x16, x16, #0xbe0
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/// br x17
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///
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/// The other type of trampolines are located in .plt.got, that are used for
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/// non-lazy bindings so doesn't use x16 arg to transfer .got entry address:
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///
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/// adrp x16, 230000
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/// ldr x17, [x16, #3040]
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/// br x17
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/// nop
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///
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uint64_t analyzePLTEntry(MCInst &Instruction, InstructionIterator Begin,
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InstructionIterator End,
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uint64_t BeginPC) const override {

‎bolt/test/AArch64/Inputs/plt-got.yaml‎

Lines changed: 216 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,216 @@
1+
--- !ELF
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FileHeader:
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Class: ELFCLASS64
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Data: ELFDATA2LSB
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Type: ET_DYN
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Machine: EM_AARCH64
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Entry: 0x10360
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ProgramHeaders:
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- Type: PT_PHDR
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Flags: [ PF_R ]
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VAddr: 0x40
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Align: 0x8
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Offset: 0x40
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- Type: PT_INTERP
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Flags: [ PF_R ]
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FirstSec: .interp
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LastSec: .interp
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VAddr: 0x270
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Offset: 0x270
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- Type: PT_LOAD
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Flags: [ PF_R ]
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FirstSec: .interp
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LastSec: .rela.dyn
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Align: 0x10000
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Offset: 0x0
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- Type: PT_LOAD
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Flags: [ PF_X, PF_R ]
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FirstSec: .plt.got
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LastSec: .text
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VAddr: 0x10350
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Align: 0x10000
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Offset: 0x2e0
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- Type: PT_LOAD
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Flags: [ PF_W, PF_R ]
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FirstSec: .interp
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LastSec: .got
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VAddr: 0x203B0
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Align: 0x10000
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Offset: 0x270
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- Type: PT_LOAD
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Flags: [ PF_W, PF_R ]
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FirstSec: .got.plt
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LastSec: .got.plt
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VAddr: 0x304E0
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Align: 0x10000
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Offset: 0x420
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- Type: PT_DYNAMIC
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Flags: [ PF_W, PF_R ]
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FirstSec: .dynamic
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LastSec: .dynamic
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VAddr: 0x203B0
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Align: 0x8
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Offset: 0x340
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- Type: PT_GNU_STACK
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Flags: [ PF_W, PF_R ]
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Offset: 0x0
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Sections:
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- Name: .interp
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Type: SHT_PROGBITS
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Flags: [ SHF_ALLOC ]
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Address: 0x270
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AddressAlign: 0x1
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Offset: 0x270
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Content: 2F6C69622F6C642D6C696E75782D616172636836342E736F2E3100
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- Name: .dynsym
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Type: SHT_DYNSYM
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Flags: [ SHF_ALLOC ]
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Address: 0x2B0
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Link: .dynstr
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AddressAlign: 0x8
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- Name: .dynstr
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Type: SHT_STRTAB
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Flags: [ SHF_ALLOC ]
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Address: 0x2E0
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AddressAlign: 0x1
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- Name: .rela.dyn
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Type: SHT_RELA
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Flags: [ SHF_ALLOC ]
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Address: 0x2F0
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Link: .dynsym
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AddressAlign: 0x8
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Relocations:
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- Offset: 0x204D8
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Symbol: abort
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Type: R_AARCH64_GLOB_DAT
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- Name: .plt.got
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Type: SHT_PROGBITS
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Flags: [ SHF_ALLOC, SHF_EXECINSTR ]
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Address: 0x10350
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AddressAlign: 0x10
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Content: 90000090116E42F920021FD61F2003D5
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- Name: .text
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Type: SHT_PROGBITS
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Flags: [ SHF_ALLOC, SHF_EXECINSTR ]
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Address: 0x10360
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AddressAlign: 0x4
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Content: FF8300D1FD7B01A9FD43009188000090086D42F9E80700F9E80740F9080100F1E8179F1AA800003701000014E80740F900013FD601000014EEFFFF97007D20D41000009010420D9100021FD61F2003D5
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- Name: .dynamic
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Type: SHT_DYNAMIC
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Flags: [ SHF_WRITE, SHF_ALLOC ]
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Address: 0x203B0
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Link: .dynstr
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AddressAlign: 0x8
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Entries:
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- Tag: DT_NEEDED
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Value: 0x1
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- Tag: DT_RELA
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Value: 0x2F0
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- Tag: DT_RELASZ
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Value: 0x18
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- Tag: DT_RELAENT
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Value: 0x18
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- Tag: DT_PLTGOT
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Value: 0x304E0
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- Tag: DT_SYMTAB
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Value: 0x2B0
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- Tag: DT_SYMENT
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Value: 0x18
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- Tag: DT_STRTAB
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Value: 0x2E0
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- Tag: DT_STRSZ
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Value: 0x10
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- Tag: DT_GNU_HASH
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Value: 0x290
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- Tag: DT_FLAGS_1
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Value: 0x8000000
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- Tag: DT_DEBUG
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Value: 0x0
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- Tag: DT_NULL
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Value: 0x0
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- Name: .got
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Type: SHT_PROGBITS
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Flags: [ SHF_WRITE, SHF_ALLOC ]
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Address: 0x204D0
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AddressAlign: 0x8
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Content: '00000000000000000000000000000000'
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- Name: .got.plt
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Type: SHT_PROGBITS
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Flags: [ SHF_WRITE, SHF_ALLOC ]
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Address: 0x304E0
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AddressAlign: 0x8
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Content: B00302000000000000000000000000000000000000000000
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- Name: .rela.text
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Type: SHT_RELA
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Flags: [ SHF_INFO_LINK ]
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Link: .symtab
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AddressAlign: 0x8
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Offset: 0x1268
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Info: .text
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Relocations:
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- Offset: 0x1036C
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Symbol: abort
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Type: R_AARCH64_ADR_GOT_PAGE
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- Offset: 0x10370
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Symbol: abort
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Type: R_AARCH64_LD64_GOT_LO12_NC
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- Offset: 0x10398
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Symbol: abort
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Type: R_AARCH64_CALL26
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- Type: SectionHeaderTable
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Sections:
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- Name: .interp
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- Name: .dynsym
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- Name: .dynstr
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- Name: .rela.dyn
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- Name: .plt.got
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- Name: .text
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- Name: .dynamic
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- Name: .got
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- Name: .got.plt
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- Name: .strtab
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- Name: .symtab
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- Name: .shstrtab
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- Name: .rela.text
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Symbols:
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- Name: .text
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Type: STT_SECTION
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Section: .text
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Value: 0x10360
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- Name: .dynamic
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Type: STT_SECTION
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Section: .dynamic
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Value: 0x203B0
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- Name: .got
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Type: STT_SECTION
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Section: .got
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Value: 0x204D0
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- Name: .got.plt
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Type: STT_SECTION
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Section: .got.plt
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Value: 0x304E0
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- Name: 'abort$got'
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Type: STT_OBJECT
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Section: .got
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Value: 0x204D8
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- Name: _start
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Type: STT_FUNC
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Section: .text
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Value: 0x10360
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Size: 0x3C
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- Name: _DYNAMIC
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Section: .dynamic
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Value: 0x203B0
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- Name: _GLOBAL_OFFSET_TABLE_
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Section: .got
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Value: 0x204D0
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- Name: abort
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Type: STT_FUNC
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Binding: STB_GLOBAL
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Size: 0x8
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DynamicSymbols:
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- Name: abort
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Type: STT_FUNC
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Binding: STB_GLOBAL
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Size: 0x8
216+
...

‎bolt/test/AArch64/plt-got.test‎

Lines changed: 7 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,7 @@
1+
// This test checks .plt.got handling by BOLT
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RUN: yaml2obj %p/Inputs/plt-got.yaml &> %t.exe
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RUN: llvm-bolt %t.exe -o %t.bolt --print-disasm --print-only=_start/1 | \
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RUN: FileCheck %s
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CHECK: bl abort@PLT

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