[PATCH] D90458: [yaml2obj] - ProgramHeaders: introduce FirstSec/LastSec instead of Sections list.

[George Rimar via Phabricator via llvm-commits]

grimar marked an inline comment as done.
grimar added inline comments.


================
Comment at: llvm/tools/obj2yaml/elf2yaml.cpp:392-399
     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});
+      if (isInSegment<ELFT>(S, Sections[S.OriginalSecNdx], Phdr)) {
+        if (!PH.FirstSec)
+          PH.FirstSec = S.Name;
+        PH.LastSec = S.Name;
+      }
----------------
jhenderson wrote:
> Does this loop work if section headers are not in section offset order? Or are they guaranteed to be by some sorting earlier on?
I have no short answer, we have a specific behavior for cases where sections are not in the
section offset order currently, let me describe it.

Imagine we have 3 sections:
.foo at offset 0x100, .bar at offset 0x200 and .zed at offset 0x300.
And lets have a section header table where they are in a different order:
.zed (0x300), .foo (0x100) and .bar (0x200).

And lets have a segment [.foo, .zed]. The YAML for this case is shown below:

```
--- !ELF
FileHeader:
  Class: ELFCLASS64
  Data:  ELFDATA2LSB
  Type:  ET_EXEC
Sections:
  - Name:    .foo
    Type:    SHT_PROGBITS
    Flags:   [ SHF_ALLOC ]
    Size:    0x1
    Offset:  0x100
  - Name:    .bar
    Type:    SHT_PROGBITS
    Flags:   [ SHF_ALLOC ]
    Size:    0x2
    Offset:  0x200
  - Name:    .zed
    Type:    SHT_PROGBITS
    Flags:   [ SHF_ALLOC ]
    Size:    0x3
    Offset:  0x300
SectionHeaderTable:
  Sections:
    - Name: .zed
    - Name: .foo
    - Name: .bar
    - Name: .strtab
    - Name: .shstrtab
ProgramHeaders:
  - Type:     PT_LOAD
    Flags:    [ PF_W, PF_R ]
    VAddr:    0x1000
    FirstSec: .foo
    LastSec:  .zed

```

after applying obj2yaml we have:


```
--- !ELF
FileHeader:
  Class:           ELFCLASS64
  Data:            ELFDATA2LSB
  Type:            ET_EXEC
ProgramHeaders:
  - Type:            PT_LOAD
    Flags:           [ PF_W, PF_R ]
    FirstSec:        .zed
    LastSec:         .bar
    VAddr:           0x0000000000001000
Sections:
  - Name:            .zed
    Type:            SHT_PROGBITS
    Flags:           [ SHF_ALLOC ]
    Address:         0x0000000000000003
    Content:         '000000'
  - Name:            .foo
    Type:            SHT_PROGBITS
    Flags:           [ SHF_ALLOC ]
    Content:         '00'
  - Name:            .bar
    Type:            SHT_PROGBITS
    Flags:           [ SHF_ALLOC ]
    Address:         0x0000000000000001
    Content:         '0000'
...
```

What is noticable:
1) We lost the information about the section header order. I.e. now
    the order is not **.foo .bar. zed**, but **.zed .foo .bar**. Because we dump sections
    by section header table order only and don't try to preserve section offsets.
2) `FirstSec`/`LastSec` were changed, but they match the YAML produced.



CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D90458/new/

https://reviews.llvm.org/D90458