[PATCH] D74955: [obj2yaml] - Dump SHT_STRTAB, SHT_SYMTAB and SHT_DYNSYM sections.

[George Rimar via Phabricator via llvm-commits]

grimar added a comment.

In D74955#1886907 <https://reviews.llvm.org/D74955#1886907>, @MaskRay wrote:

> Since rL238073 <https://reviews.llvm.org/rL238073>, clang no longer produces .shstrtab, but rather uses a unified .strtab for both section names and symbol names. Dumping `SHT_STRTAB` is necessary to differentiate the two cases.
>
> Do you mean that yaml2obj generated SHT_DYNSYM is not at the normal place (early in the section header table, somewhere before .rodata)?


No. The place is just different from the one in the original object.
See: imagine we have test.s:

  .data
  .section .bar,"a"
  .quad .bar
  
  .text
  .section .foo,"ax"
  .quad .foo
  
  .section .zed,"ax"
  .quad .foo

and do:

as test.s -o test.o
ld.bfd test.o -shared -o test.so

We have an output with the following section headers:

Section Headers:

  [Nr] Name              Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
  [ 0]                   NULL             0000000000000000  00000000
       0000000000000000  0000000000000000           0     0     0
  [ 1] .hash             HASH             0000000000000190  00000190
       0000000000000010  0000000000000004   A       3     0     8
  [ 2] .gnu.hash         GNU_HASH         00000000000001a0  000001a0
       000000000000001c  0000000000000000   A       3     0     8
  [ 3] .dynsym           DYNSYM           00000000000001c0  000001c0
       0000000000000018  0000000000000018   A       4     1     8
  [ 4] .dynstr           STRTAB           00000000000001d8  000001d8
       0000000000000001  0000000000000000   A       0     0     1
  [ 5] .rela.dyn         RELA             00000000000001e0  000001e0
       0000000000000048  0000000000000018   A       3     0     8
  [ 6] .foo              PROGBITS         0000000000001000  00001000
       0000000000000008  0000000000000000  AX       0     0     1
  [ 7] .zed              PROGBITS         0000000000001008  00001008
       0000000000000008  0000000000000000  AX       0     0     1
  [ 8] .bar              PROGBITS         0000000000002000  00002000
       0000000000000008  0000000000000000   A       0     0     1
  [ 9] .eh_frame         PROGBITS         0000000000002008  00002008
       0000000000000000  0000000000000000   A       0     0     8
  [10] .dynamic          DYNAMIC          0000000000003ef0  00002ef0
       0000000000000110  0000000000000010  WA       4     0     8
  [11] .symtab           SYMTAB           0000000000000000  00003000
       0000000000000120  0000000000000018          12    12     8
  [12] .strtab           STRTAB           0000000000000000  00003120
       000000000000000a  0000000000000000           0     0     1
  [13] .shstrtab         STRTAB           0000000000000000  0000312a
       0000000000000061  0000000000000000           0     0     1

Then after invoking obj2yaml and yaml2obj we have:

  [Nr] Name              Type             Address           Offset
        Size              EntSize          Flags  Link  Info  Align
   [ 0]                   NULL             0000000000000000  00000000
        0000000000000000  0000000000000000           0     0     0
   [ 1] .hash             HASH             0000000000000190  00000040
        0000000000000010  0000000000000000   A       9     0     8
   [ 2] .gnu.hash         GNU_HASH         00000000000001a0  00000050
        000000000000001c  0000000000000000   A       9     0     8
   [ 3] .rela.dyn         RELA             00000000000001e0  00000070
        0000000000000048  0000000000000018   A       9     0     8
   [ 4] .foo              PROGBITS         0000000000001000  000000b8
        0000000000000008  0000000000000000  AX       0     0     1
   [ 5] .zed              PROGBITS         0000000000001008  000000c0
        0000000000000008  0000000000000000  AX       0     0     1
   [ 6] .bar              PROGBITS         0000000000002000  000000c8
        0000000000000008  0000000000000000   A       0     0     1
   [ 7] .eh_frame         PROGBITS         0000000000002008  000000d0
        0000000000000000  0000000000000000   A       0     0     8
   [ 8] .dynamic          DYNAMIC          0000000000003ef0  000000d0
        0000000000000110  0000000000000010  WA      10     0     8
   [ 9] .dynsym           DYNSYM           0000000000000000  000001e0
        0000000000000018  0000000000000018   A      10     1     8
   [10] .dynstr           STRTAB           0000000000000000  000001f8
        0000000000000001  0000000000000000   A       0     0     1
   [11] .symtab           SYMTAB           0000000000000000  00000200
        0000000000000120  0000000000000018          12    12     8
   [12] .strtab           STRTAB           0000000000000000  00000320
        0000000000000050  0000000000000000           0     0     1
   [13] .shstrtab         STRTAB           0000000000000000  00000370
        0000000000000061  0000000000000000           0     0     1

Note that `.dynsym` and `.dynstr` changed their location. That happened
because obj2yaml did not dump them and hence yaml2obj added them to the end of the list,
together with `.symtab`,`.strtab` and `.shstrtab`.
With this patch it is possible to preserve the original sections order as obj2yaml starts to create placeholders for them.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D74955/new/

https://reviews.llvm.org/D74955