[llvm] [BOLT] Fix LongJmp layout estimation (PR #215416)

[Alexey Moksyakov via llvm-commits]

yavtuk wrote:

> Thank you for the review, @rafaelauler, but, unfortunately, I have realized that the patch does not fix the original issue I was investigating.
> 
> **Original issue**
> 
> The original motivation for this PR was processing a Chromium build with llvm-bolt, which resulted in several BOLT errors. All observed failures were caused by misestimating the 128 MiB range of AArch64 branch26/call26 instructions. Depending on when the out-of-range value is resolved, the failure appears either during MC emission:
> 
> ```
> <unknown>:0: error: fixup value out of range
> BOLT-ERROR: Emission failed.
> ```
> 
> or during JITLink:
> 
> ```
> BOLT-ERROR: JITLink failed: In graph in-memory object file, section .text: relocation target 0x8400048 (<anonymous symbol>:0x400040 + 0x8000008) is out of range of Branch26PCRel fixup at address 0x400040 ($x, 0x400000 + 0x4)

@adam-bzowski-arm If you have time to debug this bug, here's how I fixed a similar problem:
Branch26PCRel  related to call (bl target) instruction. You can add more log to dump Target and SignedValue, calculate call site for this relocation.

 ```
static uint64_t adjustFixupValue(const MCFixup &Fixup, const MCValue &Target,
                                 uint64_t Value, MCContext &Ctx,
                                 const Triple &TheTriple, bool IsResolved) {
.....

  case AArch64::fixup_aarch64_pcrel_branch26:
  case AArch64::fixup_aarch64_pcrel_call26:
    // Signed 28-bit immediate
    if (SignedValue > 134217727 || SignedValue < -134217728)
      Ctx.reportError(Fixup.getLoc(), "fixup value out of range");
    // Low two bits are not encoded (4-byte alignment assumed).
    if (Value & 0x3)
      Ctx.reportError(Fixup.getLoc(), "fixup not sufficiently aligned");
    return (Value >> 2) & 0x3ffffff;

.....
}
 ```

my case the issue was in getSymbolAddress, the target was in the middle of the target function.

I can try to help you with debug if you can share reproducer.


https://github.com/llvm/llvm-project/pull/215416