SHT_CREL is unsupported for sh_info

[Amichaxx]

Describe the bug

patchelf seems to miss updating sh_info for SHT_CREL sections when it reorders sections.

  [ 6] .rodata           PROGBITS        000000000162f100 162f100 f946c8 00 AMS  0   0 256
  [10] .text             PROGBITS        0000000002670000 2660000 dc80f2c 00 AXR  0   0 65536
  [16] .tdata            PROGBITS        0000000010307100 102e7100 0000c8 00 WAT  0   0 32
  [30] .crel.text        CREL            0000000000000000 10df0008 1efa4f2 00   I 41  16  8
  [37] .crel.rodata      CREL            0000000000000000 142a6c58 004d69 00   I 41  12  8
  [38] .crel.note.crashpad.info CREL     0000000000000000 142ab9c1 000008 01   I 41   3  1
  [40] .rela.tdata       RELA            0000000000000000 142abdc0 000018 18   I 41  16  8
  [48] .note.crashpad.info NOTE          000000001c931ff8 1c931ff8 000020 00   A  0   0  4

For example, .crel.text points to .tdata, but it should point to .text.

This patch is motivated by llvm/BOLT. We are unable to BOLT a (downstream) Chromium binary due to this issue.

Steps To Reproduce

I have checked and don't believe the usual nixpkgs Chromium build uses CREL, so here is a minimal repro:

cat > crel.s <<'EOF'
.section .note.creltest,"a",%note
.balign 4
target:
  .word 0

.text
.globl _start
_start:
  adrp x0, target
  add x0, x0, :lo12:target
  ret
EOF

clang -target aarch64-linux-gnu \
  -Wa,--allow-experimental-crel,--crel \
  -fuse-ld=lld \
  -nostdlib \
  -Wl,--emit-relocs \
  -Wl,-rpath,/x \
  crel.s -o repro

Expected behavior
sh_info should still point to the section being relocated after patchelf rewrites.

Version

patchelf 0.15.2

Additional context

A local patch updates sortShdrs() to add SHT_CREL, which mirrors handling for SHT_REL and SHT_RELA. Overlaying this over patchelf appears to solve the issue. Happy to, in future, post a patch if this makes sense to the community.

[Amichaxx]

I have decided to extend the reproduction in the ticket just to clarify better how this issue is isolated to patchelf.

Before patchelf:

    [Nr] Name              Type            Address          Off    Size   ES Flg Lk Inf Al
    [ 3] .gnu.hash         GNU_HASH        000000000000aab0 00aab0 0001b0 00   A 45   0  8
    [ 6] .rodata           PROGBITS        000000000162f100 162f100 f946c8 00 AMS  0   0 256
    [10] .text             PROGBITS        0000000002670000 2660000 dc80f2c 00 AXR  0   0 65536
    [12] .fini             PROGBITS        00000000102f0f50 102e0f50 000014 00  AX  0   0  4
    [16] .tdata            PROGBITS        0000000010307100 102e7100 0000c8 00 WAT  0   0 32
    [30] .crel.text        CREL            0000000000000000 10df0008 1efa4f2 00   I 41  16  8
    [37] .crel.rodata      CREL            0000000000000000 142a6c58 004d69 00   I 41  12  8
    [38] .crel.note.crashpad.info CREL     0000000000000000 142ab9c1 000008 01   I 41   3  1
    [40] .rela.tdata       RELA            0000000000000000 142abdc0 000018 18   I 41  16  8
    [48] .note.crashpad.info NOTE          000000001c931ff8 1c931ff8 000020 00   A  0   0  4

After patchelf:

    [Nr] Name              Type            Address          Off    Size   ES Flg Lk Inf Al
    [ 3] .gnu.hash         GNU_HASH        000000000000aab0 00aab0 0001b0 00   A 45   0  8
    [ 6] .rodata           PROGBITS        000000000162f100 162f100 f946c8 00 AMS  0   0 256
    [10] .text             PROGBITS        0000000002670000 2660000 dc80f2c 00 AXR  0   0 65536
    [12] .fini             PROGBITS        00000000102f0f50 102e0f50 000014 00  AX  0   0  4
    [16] .tdata            PROGBITS        0000000010307100 102e7100 0000c8 00 WAT  0   0 32
    [30] .crel.text        CREL            0000000000000000 10df0008 1efa4f2 00   I 41  10  8
    [37] .crel.rodata      CREL            0000000000000000 142a6c58 004d69 00   I 41   6  8
    [38] .crel.note.crashpad.info CREL     0000000000000000 142ab9c1 000008 01   I 41  48  1
    [40] .rela.tdata       RELA            0000000000000000 142abdc0 000018 18   I 41  16  8
    [48] .note.crashpad.info NOTE          000000001c931ff8 1c931ff8 000020 00   A  0   0  4

As shown, .crel.text points to .tdata, but it should point to .text.