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[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$pb@ha
addi 30, 30, .got2+0x8000-.L1$pb@l
...
bl foo+0x8000@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$pb@ha
addi 30, 30, .got2+0x8000-.L1+ppc32Got2OutSecOff$pb@ha$pb@l
...
bl foo+0x8000+ppc32Got2OutSecOff@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
This commit is contained in:
Fangrui Song 2020-01-28 00:01:20 -08:00
parent a1f6ff2681
commit e11b709b19
2 changed files with 49 additions and 0 deletions
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8
lld/ELF/InputSection.cpp
View File

@ -485,6 +485,14 @@ void InputSection::copyRelocations(uint8_t *buf, ArrayRef<RelTy> rels) {
p->r_addend = sym.getVA(addend) - section->getOutputSection()->addr;
else if (config->relocatable && type != target->noneRel)
sec->relocations.push_back({R_ABS, type, rel.r_offset, addend, &sym});
} else if (config->emachine == EM_PPC && type == R_PPC_PLTREL24 &&
p->r_addend >= 0x8000) {
// Similar to R_MIPS_GPREL{16,32}. If the addend of R_PPC_PLTREL24
// indicates that r30 is relative to the input section .got2
// (r_addend>=0x8000), after linking, r30 should be relative to the output
// section .got2 . To compensate for the shift, adjust r_addend by
// ppc32Got2OutSecOff.
p->r_addend += sec->file->ppc32Got2OutSecOff;
}
}
}

41
lld/test/ELF/ppc32-relocatable-got2.s Normal file
View File

@ -0,0 +1,41 @@
# REQUIRES: ppc
## Test addend adjustment of R_PPC_PLTREL24 when copying relocations.
## If r_addend indicates .got2, adjust it by the local .got2's output section offset.
# RUN: llvm-mc -filetype=obj -triple=powerpc %s -o %t.o
# RUN: ld.lld -r %t.o %t.o -o %t
# RUN: llvm-readobj -r %t | FileCheck %s
# RUN: ld.lld -shared --emit-relocs %t.o %t.o -o %t.so
# RUN: llvm-readobj -r %t.so | FileCheck %s
# CHECK: .rela.adjust {
# CHECK-NEXT: R_PPC_REL16_HA .got2 0x8002
# CHECK-NEXT: R_PPC_REL16_LO .got2 0x8006
# CHECK-NEXT: R_PPC_PLTREL24 foo 0x8000
# CHECK-NEXT: R_PPC_PLTREL24 bar 0x8000
# CHECK-NEXT: R_PPC_REL16_HA .got2 0x8006
# CHECK-NEXT: R_PPC_REL16_LO .got2 0x800A
# CHECK-NEXT: R_PPC_PLTREL24 foo 0x8004
# CHECK-NEXT: R_PPC_PLTREL24 bar 0x8004
# CHECK-NEXT: }
# CHECK-NEXT: .rela.no_adjust {
# CHECK-NEXT: R_PPC_PLTREL24 foo 0x0
# CHECK-NEXT: R_PPC_PLTREL24 foo 0x0
# CHECK-NEXT: }
.section .got2,"aw"
.long 0
.section .adjust,"ax"
bcl 20,30,.L0
.L0:
addis 30,30,.got2+0x8000-.L0@ha
addi 30,30,.got2+0x8000-.L0@l
## Refers to .got2+addend, adjust.
bl foo+0x8000@plt
bl bar+0x8000@plt
.section .no_adjust,"ax"
## Refers to .got, no adjustment.
bl foo@plt