[obj2yaml] - Do not dump the segment's "Align" field when it is equal to 1.

[grimar]

Summary

yaml2obj sets the Align to 1 by default, hence we can stop
dumping it to reduce the output.

[MaskRay]

Looks great!

llvm/tools/obj2yaml/elf2yaml.cpp

322

Omit it to reduce output?

[jhenderson]

LGTM.

[grimar]

llvm/tools/obj2yaml/elf2yaml.cpp

322

I'd keep the current version: as we already have the another comment in this file saying almost the same: "Generally we are trying to reduce noise in the YAML output.". (I am not sure that "reducing the output" is better describes our goal, we want to omit unnessesary parts, it is very close and reduces the output, but is not 100% the same probably.)

llvm/test/Object/obj2yaml.test

 # ELF-AVR-NEXT:     - Section: .data
 # ELF-AVR-NEXT:    Align: 0x0000000000000002
 # ELF-AVR-NEXT:  - Type:  PT_LOAD
 # ELF-AVR-NEXT:    Flags: [ PF_W, PF_R ]
 # ELF-AVR-NEXT:    Sections:
 # ELF-AVR-NEXT:     - Section: .data
 # ELF-AVR-NEXT:    VAddr: 0x0000000000800060
 # ELF-AVR-NEXT:    PAddr: 0x0000000000000004
-# ELF-AVR-NEXT:    Align: 0x0000000000000001
 # ELF-AVR-NEXT: Sections:
 # ELF-AVR-NEXT:   - Name:            .text
 # ELF-AVR-NEXT:     Type:            SHT_PROGBITS
 # ELF-AVR-NEXT:     Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
 # ELF-AVR-NEXT:     AddressAlign:    0x0000000000000002
 # ELF-AVR-NEXT:     Content:         C20E0895
 # ELF-AVR-NEXT:   - Name:            .data
 # ELF-AVR-NEXT:     Type:            SHT_PROGBITS

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

 # YAML-NEXT:      - Section: .dynamic
 # YAML-NEXT:    VAddr: 0x0000000000003EF0
 # YAML-NEXT:    Align: 0x0000000000000008
 # YAML-NEXT:  - Type:  PT_GNU_RELRO
 # YAML-NEXT:    Flags: [ PF_R ]
 # YAML-NEXT:    Sections:
 # YAML-NEXT:      - Section: .dynamic
 # YAML-NEXT:    VAddr: 0x0000000000003EF0
-# YAML-NEXT:    Align: 0x0000000000000001
 # YAML-NEXT:  - Type:  PT_LOAD
 # YAML-NEXT:    Flags: [ PF_R ]
 # YAML-NEXT:    VAddr: 0x0000000000004000
-# YAML-NEXT:    Align: 0x0000000000000001
 # YAML-NEXT:  - Type:  PT_LOAD
 # YAML-NEXT:    Flags: [ PF_R ]
 # YAML-NEXT:    Sections:
 # YAML-NEXT:      - Section: .gnu.hash
 # YAML-NEXT:    VAddr: 0x00000000000001A0
-# YAML-NEXT:    Align: 0x0000000000000001
 # YAML-NEXT:  - Type:  PT_LOAD
 # YAML-NEXT:    Flags: [ PF_R ]
 # YAML-NEXT:    Sections:
 # YAML-NEXT:      - Section: .gnu.hash
 # YAML-NEXT:    VAddr: 0x00000000000001A0
-# YAML-NEXT:    Align: 0x0000000000000001
 # YAML-NEXT: Sections:
 
 --- !ELF
 FileHeader:
   Class:   ELFCLASS64
   Data:    ELFDATA2LSB
   Type:    ET_DYN
   Machine: EM_X86_64
- Type:  PT_DYNAMIC
     Flags: [ PF_W, PF_R ]
     Sections:
       - Section: .dynamic
     VAddr: 0x3EF0
     Align: 0x8
 ## Show we can create a relro segment and put a section into it.
 ## We used .dynamic here and in tests above to demonstrate that
 ## we can place a section in any number of segments.
+## Also, we explicitly set the "Align" property to 1 to demonstate
+## that we do not dump it, because it is the default alignment
+## value set by yaml2obj.
   - Type:  PT_GNU_RELRO
     Flags: [ PF_R ]
     Sections:
       - Section: .dynamic
     VAddr: 0x3EF0
     Align: 0x1
 ## Show we can dump a standalone empty segment.
   - Type:  PT_LOAD

 # EMPTY-NEXT:     - Section: .empty.tls.end
 # EMPTY-NEXT:   VAddr: 0x0000000000001000
 # EMPTY-NEXT:   Align: 0x0000000000001000
 # EMPTY-NEXT: - Type:            PT_TLS
 # EMPTY-NEXT:   Flags:           [ PF_W, PF_R ]
 # EMPTY-NEXT:   Sections:
 # EMPTY-NEXT:     - Section:         .empty.tls.start
 # EMPTY-NEXT:   VAddr:           0x0000000000001000
-# EMPTY-NEXT:   Align:           0x0000000000000001
 # EMPTY-NEXT: - Type:            PT_TLS
 # EMPTY-NEXT:   Flags:           [ PF_W, PF_R ]
 # EMPTY-NEXT:   Sections:
 # EMPTY-NEXT:     - Section:         .empty.tls.middle
 # EMPTY-NEXT:   VAddr:           0x0000000000001100
-# EMPTY-NEXT:   Align:           0x0000000000000001
 # EMPTY-NEXT: - Type:            PT_TLS
 # EMPTY-NEXT:   Flags:           [ PF_W, PF_R ]
 # EMPTY-NEXT:   Sections:
 # EMPTY-NEXT:     - Section:         .empty.tls.end
 # EMPTY-NEXT:   VAddr:           0x0000000000001200
-# EMPTY-NEXT:   Align:           0x0000000000000001
 # EMPTY-NEXT: Sections:
 
 --- !ELF
 FileHeader:
   Class:   ELFCLASS64
   Data:    ELFDATA2LSB
   Type:    ET_DYN
   Machine: EM_X86_64

 # NON-ALLOC:      ProgramHeaders:
 # NON-ALLOC-NEXT:   - Type:  PT_LOAD
 # NON-ALLOC-NEXT:     Flags: [ PF_R ]
 # NON-ALLOC-NEXT:     Sections:
 # NON-ALLOC-NEXT:      - Section: .alloc.1
 # NON-ALLOC-NEXT:      - Section: .non-alloc.1
 # NON-ALLOC-NEXT:      - Section: .alloc.2
 # NON-ALLOC-NEXT:     VAddr: 0x0000000000001000
-# NON-ALLOC-NEXT:     Align: 0x0000000000000001
 # NON-ALLOC-NEXT: Sections:
 
 --- !ELF
 FileHeader:
   Class:   ELFCLASS64
   Data:    ELFDATA2LSB
   Type:    ET_DYN
   Machine: EM_X86_64

llvm/tools/obj2yaml/elf2yaml.cpp

if (!PhdrsOrErr)
     return PhdrsOrErr.takeError();
 
   for (const typename ELFT::Phdr &Phdr : *PhdrsOrErr) {
     ELFYAML::ProgramHeader PH;
     PH.Type = Phdr.p_type;
     PH.Flags = Phdr.p_flags;
     PH.VAddr = Phdr.p_vaddr;
     PH.PAddr = Phdr.p_paddr;
+
+    // yaml2obj sets the alignment of a segment to 1 by default.
+    // We do not print the default alignment to reduce noise in the output.
+    if (Phdr.p_align != 1)
       PH.Align = static_cast<llvm::yaml::Hex64>(Phdr.p_align);
 
     // Here we match sections with segments.
     // It is not possible to have a non-Section chunk, because
     // obj2yaml does not create Fill chunks.
     for (const std::unique_ptr<ELFYAML::Chunk> &C : Chunks) {
       ELFYAML::Section &S = cast<ELFYAML::Section>(*C.get());
       if (isInSegment<ELFT>(S, Sections[S.OriginalSecNdx], Phdr))
         PH.Sections.push_back({S.Name});