[all-commits] [llvm/llvm-project] a2639d: [ORC] Add a utility for adding missing "self" relo...

[Ben Langmuir via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: a2639dcbe613bb2e219a50171f322d7ac1dc8de1
      https://github.com/llvm/llvm-project/commit/a2639dcbe613bb2e219a50171f322d7ac1dc8de1
  Author: Ben Langmuir <blangmuir at apple.com>
  Date:   2021-11-04 (Thu, 04 Nov 2021)

  Changed paths:
    M llvm/include/llvm/ExecutionEngine/Orc/IndirectionUtils.h
    M llvm/include/llvm/MC/MCInstrAnalysis.h
    M llvm/lib/ExecutionEngine/Orc/CMakeLists.txt
    M llvm/lib/ExecutionEngine/Orc/IndirectionUtils.cpp
    M llvm/lib/MC/MCInstrAnalysis.cpp
    M llvm/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.cpp
    A llvm/test/ExecutionEngine/JITLink/X86/Inputs/x86-64_self_relocation.s
    A llvm/test/ExecutionEngine/JITLink/X86/MachO_x86-64_self_relocation.test
    A llvm/test/ExecutionEngine/JITLink/X86/MachO_x86-64_self_relocation_exec.test
    M llvm/tools/llvm-jitlink/llvm-jitlink.cpp

  Log Message:
  -----------
  [ORC] Add a utility for adding missing "self" relocations to a Symbol

If a tool wants to introduce new indirections via stubs at link-time in
ORC, it can cause fidelity issues around the address of the function if
some references to the function do not have relocations. This is known
to happen inside the body of the function itself on x86_64 for example,
where a PC-relative address is formed, but without a relocation.

```
_foo:
  leaq -7(%rip), %rax ## form pointer to '_foo' without relocation

_bar:
  leaq (%rip), %rax ##  uses X86_64_RELOC_SIGNED to '_foo'
```

The consequence of introducing a stub for such a function at link time
is that if it forms a pointer to itself without relocation, it will not
have the same value as a pointer from outside the function. If the
function pointer is used as a key, this can cause problems.

This utility provides best-effort support for adding such missing
relocations using MCDisassembler and MCInstrAnalysis to identify the
problematic instructions. Currently it is only implemented for x86_64.

Note: the related issue with call/jump instructions is not handled
here, only forming function pointers.

rdar://83514317

Differential revision: https://reviews.llvm.org/D113038