[all-commits] [llvm/llvm-project] 2bfee3: [MC][ELF] Emit a relocation if target is defined i...

[Fangrui Song via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 2bfee35cb860859b436de0b780fbd00d68e198a4
      https://github.com/llvm/llvm-project/commit/2bfee35cb860859b436de0b780fbd00d68e198a4
  Author: Fangrui Song <maskray at google.com>
  Date:   2020-01-12 (Sun, 12 Jan 2020)

  Changed paths:
    M lld/test/ELF/global-offset-table-position-aarch64.s
    M llvm/lib/MC/ELFObjectWriter.cpp
    M llvm/test/MC/ARM/thumb1-branch-reloc.s
    M llvm/test/MC/ARM/thumb2-beq-fixup.s
    R llvm/test/MC/ELF/relax.s
    A llvm/test/MC/ELF/target-in-same-section.s
    M llvm/test/MC/X86/align-branch-64-2a.s
    M llvm/test/MC/X86/align-branch-64-2b.s
    M llvm/test/MC/X86/align-branch-64-2c.s

  Log Message:
  -----------
  [MC][ELF] Emit a relocation if target is defined in the same section and is non-local

For a target symbol defined in the same section, currently we don't emit
a relocation if VariantKind is VK_None (with few exceptions like RISC-V
relaxation), while GNU as emits one. This causes program behavior
differences with and without -ffunction-sections, and can break intended
symbol interposition in a -shared link.

```
.globl foo
foo:
  call foo      # no relocation. On other targets, may be written as b foo, etc
  call bar      # a relocation if bar is in another section (e.g. -ffunction-sections)
  call foo at plt  # a relocation
```

Unify these cases by always emitting a relocation. If we ever want to
optimize `call foo` in -shared links, we should emit a STB_LOCAL alias
and call via the alias.

ARM/thumb2-beq-fixup.s: we now emit a relocation to global_thumb_fn as GNU as does.
X86/Inputs/align-branch-64-2.s: we now emit R_X86_64_PLT32 to foo as GNU does.

ELF/relax.s: rewrite the test as target-in-same-section.s .
We omitted relocations to `global` and now emit R_X86_64_PLT32.
Note, GNU as does not emit a relocation for `jmp global` (maybe its own
bug). Our new behavior is compatible except `jmp global`.

Reviewed By: peter.smith

Differential Revision: https://reviews.llvm.org/D72197