[llvm] r293224 - [obj2yaml] Produce correct output for invalid relocations.

[Davide Italiano via llvm-commits]

On Fri, Jan 27, 2017 at 10:27 AM, Rafael Avila de Espindola
<rafael.espindola at gmail.com> wrote:
> Passing the result object back via yam2obj will produce a different
> result, no?
>

A bit. I may be wrong, but I think you can obtain an isomorphism even
without this change (as sections are laid out differently).

Both files contain the 'correct' reloc, which was the purpose of the test:

$ objdump -r array.o
RELOCATION RECORDS FOR [.text]:
OFFSET           TYPE              VALUE
0000000000000000 R_X86_64_NONE     *ABS*

$ objdump -r reverse.o
RELOCATION RECORDS FOR [.text]:
OFFSET           TYPE              VALUE
0000000000000000 R_X86_64_NONE     *ABS*

We now create `.shstrtab` in the inverted relocatable (which doesn't
appear in the original object).

$ readelf -S array.o
Section Headers:
  [Nr] Name              Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
  [ 0]                   NULL             0000000000000000  00000000
       0000000000000000  0000000000000000           0     0     0
  [ 1] .text             PROGBITS         0000000000000000  000001c0
       0000000000000005  0000000000000000  AX       0     0     4
  [ 2] .rela.text        RELA             0000000000000000  000001c8
       0000000000000018  0000000000000018           3     1     8
  [ 3] .symtab           SYMTAB           0000000000000000  000001e0
       0000000000000060  0000000000000018           4     2     8
  [ 4] .strtab           STRTAB           0000000000000000  00000240
       0000000000000044  0000000000000000           0     0     1
  [ 5] .shstrtab         STRTAB           0000000000000000  00000284
       0000000000000026  0000000000000000           0     0     1

$ readelf -S reverse.o
Section Headers:
  [Nr] Name              Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
  [ 0]                   NULL             0000000000000000  00000000
       0000000000000000  0000000000000000           0     0     0
  [ 1] .strtab           STRTAB           0000000000000000  00000040
       0000000000000070  0000000000000000           0     0     1
  [ 2] .text             PROGBITS         0000000000000000  000000b0
       0000000000000005  0000000000000000  AX       0     0     4
  [ 3] .rela.text        RELA             0000000000000000  000000b8
       0000000000000018  0000000000000018           4     2     8
  [ 4] .symtab           SYMTAB           0000000000000000  000000d0
       0000000000000060  0000000000000018           1     2     8

Even without the `.shstrtabe` section emitted, the order of the
section header is different in the two executables, so I don't think
you were obtaining the original object back anyway.

--
Davide