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[obj2yaml] Emit ProgramHeader.Offset
Currently, obj2yaml doesn't emit the offset of program headers, leaving it to yaml2obj to calculate offsets based on `FirstSec` and `LastSec`. This causes an obj2yaml->yaml2obj round trip to often produce an ELF file that is not equivalent to the original, especially since it seems common to have program headers at offset 0 whose first section starts at a higher address. Besides being non-equivalent, the produced ELF files also do not seem to work propery and readelf complains about them. Taking a simple hello world program in C, compiled using either GCC or Clang, the original ELF file has the following program headers (only showing some relevant ones): ``` Program Headers: Type Offset VirtAddr PhysAddr FileSiz MemSiz Flags Align PHDR 0x0000000000000040 0x0000000000000040 0x0000000000000040 0x00000000000002d8 0x00000000000002d8 R 0x8 INTERP 0x0000000000000318 0x0000000000000318 0x0000000000000318 0x000000000000001c 0x000000000000001c R 0x1 [Requesting program interpreter: /lib64/ld-linux-x86-64.so.2] LOAD 0x0000000000000000 0x0000000000000000 0x0000000000000000 0x0000000000000630 0x0000000000000630 R 0x1000 LOAD 0x0000000000001000 0x0000000000001000 0x0000000000001000 0x0000000000000161 0x0000000000000161 R E 0x1000 ... Section to Segment mapping: Segment Sections... 00 01 .interp 02 .interp .note.gnu.property .note.gnu.build-id .note.ABI-tag .gnu.hash .dynsym .dynstr .gnu.version .gnu.version_r .rela.dyn .rela.plt 03 .init .plt .text .fini ... ``` While this is the result of an obj2yaml->yaml2obj round trip: ``` Program Headers: Type Offset VirtAddr PhysAddr FileSiz MemSiz Flags Align PHDR 0x0000000000000000 0x0000000000000040 0x0000000000000040 0x0000000000000000 0x0000000000000000 R 0x8 readelf: Error: the PHDR segment is not covered by a LOAD segment INTERP 0x0000000000000318 0x0000000000000318 0x0000000000000318 0x000000000000001c 0x000000000000001c R 0x1 [Requesting program interpreter: /lib64/ld-linux-x86-64.so.2] LOAD 0x0000000000000318 0x0000000000000000 0x0000000000000000 0x0000000000000318 0x0000000000000318 R 0x1000 LOAD 0x0000000000001000 0x0000000000001000 0x0000000000001000 0x0000000000000161 0x0000000000000161 R E 0x1000 ... Section to Segment mapping: Segment Sections... 00 01 .interp 02 03 .init .plt .text .fini ... ``` Note that the offset of segment 2 changed from 0x0 to 0x318. This has two effects: - readelf complains "Error: the PHDR segment is not covered by a LOAD segment" since PHDR was originally covered by segment 2 but not anymore; - Segment 2 effectively became empty according to the section to segment mapping. I addition to these, the output doesn't correctly execute anymore, crashing with a "SIGSEGV (Address boundary error)". This patch fixes the difference in program header layout after a round trip by explicitly emitting offsets. Reviewed By: MaskRay Differential Revision: https://reviews.llvm.org/D145555
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‎llvm/test/Object/obj2yaml.test‎

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Original file line numberDiff line numberDiff line change
@@ -711,12 +711,14 @@ FileHeader:
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# ELF-AVR-NEXT: FirstSec: .text
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# ELF-AVR-NEXT: LastSec: .text
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# ELF-AVR-NEXT: Align: 0x2
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# ELF-AVR-NEXT: Offset: 0x74
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# ELF-AVR-NEXT: - Type: PT_LOAD
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# ELF-AVR-NEXT: Flags: [ PF_W, PF_R ]
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# ELF-AVR-NEXT: FirstSec: .data
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# ELF-AVR-NEXT: LastSec: .data
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# ELF-AVR-NEXT: VAddr: 0x800060
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# ELF-AVR-NEXT: PAddr: 0x4
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# ELF-AVR-NEXT: Offset: 0x78
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# ELF-AVR-NEXT: Sections:
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# ELF-AVR-NEXT: - Name: .text
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# ELF-AVR-NEXT: Type: SHT_PROGBITS

‎llvm/test/tools/obj2yaml/ELF/program-headers.yaml‎

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@@ -42,48 +42,57 @@
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# YAML-NEXT: FirstSec: .hash
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# YAML-NEXT: LastSec: .dynstr
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# YAML-NEXT: Align: 0x1000
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# YAML-NEXT: Offset: 0x0
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# YAML-NEXT: - Type: PT_LOAD
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# YAML-NEXT: Flags: [ PF_X, PF_R ]
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# YAML-NEXT: FirstSec: .foo
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# YAML-NEXT: LastSec: .zed
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# YAML-NEXT: VAddr: 0x1000
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# YAML-NEXT: Align: 0x1000
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# YAML-NEXT: Offset: 0x281
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# YAML-NEXT: - Type: PT_LOAD
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# YAML-NEXT: Flags: [ PF_R ]
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# YAML-NEXT: FirstSec: '.foo (1)'
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# YAML-NEXT: LastSec: .baz
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# YAML-NEXT: VAddr: 0x2000
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# YAML-NEXT: Align: 0x1000
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# YAML-NEXT: Offset: 0x291
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# YAML-NEXT: - Type: PT_LOAD
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# YAML-NEXT: Flags: [ PF_W, PF_R ]
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# YAML-NEXT: FirstSec: .dynamic
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# YAML-NEXT: LastSec: .dynamic.tail
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# YAML-NEXT: VAddr: 0x3EF0
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# YAML-NEXT: Align: 0x1000
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# YAML-NEXT: Offset: 0x29A
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# YAML-NEXT: - Type: PT_DYNAMIC
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# YAML-NEXT: Flags: [ PF_W, PF_R ]
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# YAML-NEXT: FirstSec: .dynamic
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# YAML-NEXT: LastSec: .dynamic
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# YAML-NEXT: VAddr: 0x3EF0
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# YAML-NEXT: Align: 0x8
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# YAML-NEXT: Offset: 0x29A
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# YAML-NEXT: - Type: PT_GNU_RELRO
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# YAML-NEXT: Flags: [ PF_R ]
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# YAML-NEXT: FirstSec: .dynamic
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# YAML-NEXT: LastSec: .dynamic
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# YAML-NEXT: VAddr: 0x3EF0
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# YAML-NEXT: Offset: 0x29A
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# YAML-NEXT: - Type: PT_LOAD
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# YAML-NEXT: Flags: [ PF_R ]
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# YAML-NEXT: VAddr: 0x4000
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# YAML-NEXT: Offset: 0x0
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# YAML-NEXT: - Type: PT_LOAD
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# YAML-NEXT: Flags: [ PF_R ]
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# YAML-NEXT: FirstSec: .gnu.hash
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# YAML-NEXT: LastSec: .gnu.hash
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# YAML-NEXT: VAddr: 0x1A0
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# YAML-NEXT: Offset: 0x248
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# YAML-NEXT: - Type: PT_LOAD
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# YAML-NEXT: Flags: [ PF_R ]
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# YAML-NEXT: FirstSec: .gnu.hash
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# YAML-NEXT: LastSec: .gnu.hash
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# YAML-NEXT: VAddr: 0x1A0
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# YAML-NEXT: Offset: 0x248
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# YAML-NEXT: Sections:
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--- !ELF
@@ -233,21 +242,25 @@ DynamicSymbols: []
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# EMPTY-NEXT: LastSec: .empty.tls.end
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# EMPTY-NEXT: VAddr: 0x1000
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# EMPTY-NEXT: Align: 0x1000
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# EMPTY-NEXT: Offset: 0x120
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# EMPTY-NEXT: - Type: PT_TLS
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# EMPTY-NEXT: Flags: [ PF_W, PF_R ]
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# EMPTY-NEXT: FirstSec: .empty.tls.start
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# EMPTY-NEXT: LastSec: .empty.tls.start
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# EMPTY-NEXT: VAddr: 0x1000
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# EMPTY-NEXT: Offset: 0x120
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# EMPTY-NEXT: - Type: PT_TLS
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# EMPTY-NEXT: Flags: [ PF_W, PF_R ]
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# EMPTY-NEXT: FirstSec: .empty.tls.middle
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# EMPTY-NEXT: LastSec: .empty.tls.middle
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# EMPTY-NEXT: VAddr: 0x1100
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# EMPTY-NEXT: Offset: 0x220
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# EMPTY-NEXT: - Type: PT_TLS
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# EMPTY-NEXT: Flags: [ PF_W, PF_R ]
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# EMPTY-NEXT: FirstSec: .empty.tls.end
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# EMPTY-NEXT: LastSec: .empty.tls.end
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# EMPTY-NEXT: VAddr: 0x1200
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# EMPTY-NEXT: Offset: 0x320
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# EMPTY-NEXT: Sections:
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--- !ELF
@@ -322,6 +335,7 @@ Sections:
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# MISALIGNED-YAML-NEXT: LastSec: .foo
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# MISALIGNED-YAML-NEXT: VAddr: 0x1000
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# MISALIGNED-YAML-NEXT: Align: 0x1000
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# MISALIGNED-YAML-NEXT: Offset: 0x77
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# MISALIGNED-YAML-NEXT: Sections:
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--- !ELF
@@ -354,18 +368,22 @@ Sections:
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# NON-ALLOC-NEXT: Flags: [ PF_R ]
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# NON-ALLOC-NEXT: FirstSec: .alloc.1
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# NON-ALLOC-NEXT: LastSec: .non-alloc.1
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# NON-ALLOC-NEXT: Offset: 0x120
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# NON-ALLOC-NEXT: - Type: PT_LOAD
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# NON-ALLOC-NEXT: Flags: [ PF_R ]
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# NON-ALLOC-NEXT: FirstSec: .alloc.1
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# NON-ALLOC-NEXT: LastSec: .non-alloc.1
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# NON-ALLOC-NEXT: Offset: 0x120
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# NON-ALLOC-NEXT: - Type: PT_LOAD
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# NON-ALLOC-NEXT: Flags: [ PF_R ]
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# NON-ALLOC-NEXT: FirstSec: .alloc.2
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# NON-ALLOC-NEXT: LastSec: .alloc.2
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# NON-ALLOC-NEXT: Offset: 0x230
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# NON-ALLOC-NEXT: - Type: PT_LOAD
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# NON-ALLOC-NEXT: Flags: [ PF_R ]
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# NON-ALLOC-NEXT: FirstSec: .alloc.1
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# NON-ALLOC-NEXT: LastSec: .alloc.2
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# NON-ALLOC-NEXT: Offset: 0x120
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# NON-ALLOC-NEXT: Sections:
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--- !ELF
@@ -418,23 +436,28 @@ Sections:
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# NOBITS-NEXT: Flags: [ PF_W, PF_R ]
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# NOBITS-NEXT: FirstSec: .bss
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# NOBITS-NEXT: LastSec: .bss
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# NOBITS-NEXT: Offset: 0x159
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# NOBITS-NEXT: - Type: PT_LOAD
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# NOBITS-NEXT: Flags: [ PF_W, PF_R ]
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# NOBITS-NEXT: FirstSec: .data.1
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# NOBITS-NEXT: LastSec: .bss
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# NOBITS-NEXT: Offset: 0x158
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# NOBITS-NEXT: - Type: PT_LOAD
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# NOBITS-NEXT: Flags: [ PF_W, PF_R ]
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# NOBITS-NEXT: FirstSec: .data.1
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# NOBITS-NEXT: LastSec: .data.2
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# NOBITS-NEXT: Offset: 0x158
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# NOBITS-NEXT: - Type: PT_LOAD
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# NOBITS-NEXT: Flags: [ PF_W, PF_R ]
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# NOBITS-NEXT: FirstSec: .bss
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# NOBITS-NEXT: LastSec: .data.2
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# NOBITS-NEXT: Offset: 0x159
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# NOBITS-NEXT: - Type: PT_LOAD
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# NOBITS-NEXT: Flags: [ PF_W, PF_R ]
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# NOBITS-NEXT: FirstSec: .foo.bss
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# NOBITS-NEXT: LastSec: .bar.bss
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# NOBITS-NEXT: VAddr: 0x200000000
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# NOBITS-NEXT: Offset: 0x15A
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# NOBITS-NEXT: Sections:
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--- !ELF
@@ -581,6 +604,7 @@ Sections:
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# ZERO-SIZE-NEXT: FirstSec: .empty.bar1
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# ZERO-SIZE-NEXT: LastSec: .empty.bar2
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# ZERO-SIZE-NEXT: VAddr: 0x2000
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# ZERO-SIZE-NEXT: Offset: 0x78
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# ZERO-SIZE-NEXT: Sections:
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--- !ELF

‎llvm/tools/obj2yaml/elf2yaml.cpp‎

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Original file line numberDiff line numberDiff line change
@@ -484,6 +484,7 @@ ELFDumper<ELFT>::dumpProgramHeaders(
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PH.Flags = Phdr.p_flags;
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PH.VAddr = Phdr.p_vaddr;
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PH.PAddr = Phdr.p_paddr;
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PH.Offset = Phdr.p_offset;
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// yaml2obj sets the alignment of a segment to 1 by default.
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// We do not print the default alignment to reduce noise in the output.

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