[all-commits] [llvm/llvm-project] 684c21: [ELF][PPC32] Support --emit-relocs link of R_PPC_P...

[Fangrui Song via All-commits]

  Branch: refs/heads/release/10.x
  Home:   https://github.com/llvm/llvm-project
  Commit: 684c216d73cdcd64fc0186b533870cb79dc03810
      https://github.com/llvm/llvm-project/commit/684c216d73cdcd64fc0186b533870cb79dc03810
  Author: Fangrui Song <i at maskray.me>
  Date:   2020-01-28 (Tue, 28 Jan 2020)

  Changed paths:
    M lld/ELF/InputSection.cpp
    A lld/test/ELF/ppc32-relocatable-got2.s

  Log Message:
  -----------
  [ELF][PPC32] Support --emit-relocs link of R_PPC_PLTREL24

Similar to R_MIPS_GPREL16 and R_MIPS_GPREL32 (D45972).

If the addend of an R_PPC_PLTREL24 is >= 0x8000, it indicates that r30
is relative to the input section .got2.

```
addis 30, 30, .got2+0x8000-.L1$pb at ha
addi 30, 30, .got2+0x8000-.L1$pb at l
...
bl foo+0x8000 at PLT
```

After linking, the relocation will be relative to the output section .got2.
To compensate for the shift `address(input section .got2) - address(output section .got2) = ppc32Got2OutSecOff`, adjust by `ppc32Got2OutSecOff`:

```
addis 30, 30, .got2+0x8000-.L1+ppc32Got2OutSecOff$pb at ha
addi 30, 30, .got2+0x8000-.L1+ppc32Got2OutSecOff$pb at ha$pb at l
...
bl foo+0x8000+ppc32Got2OutSecOff at PLT
```

This rule applys to a relocatable link or a non-relocatable link with --emit-relocs.

Reviewed By: Bdragon28

Differential Revision: https://reviews.llvm.org/D73532

(cherry picked from commit e11b709b1922ca46b443fcfa5d76b87edca48721)