[LLD][ARM] Add R_ARM_RELATIVE to relocations that can be applied to GotSection

[peter.smith]

Summary

When compiling -fpie and linking with the --pie option the R_ARM_GOTBREL relocation to D is resolved by writing the value of D into the .got slot and emitting an R_ARM_RELATIVE relocation for it.

Unfortunately R_ARM_RELATIVE is missing from relocateOne() leading to an unsupported relocation error (and then a segfault by the error handling system as it tries to look up the source for the GotSection.

The simple fix is to add R_ARM_RELATIVE to relocateOne() as R_ABS.

The R_ARM_GOTBREL relocation is present in the glibc library startup code so this problem will affect all --pie applications.

[ruiu]

LGTM

lld/trunk/ELF/Target.cpp

void ARMTargetInfo::relocateOne(uint8_t *Loc, uint32_t Type,
   switch (Type) {
   case R_ARM_ABS32:
   case R_ARM_BASE_PREL:
   case R_ARM_GLOB_DAT:
   case R_ARM_GOTOFF32:
   case R_ARM_GOT_BREL:
   case R_ARM_GOT_PREL:
   case R_ARM_REL32:
+  case R_ARM_RELATIVE:
   case R_ARM_TARGET1:
   case R_ARM_TARGET2:
   case R_ARM_TLS_GD32:
   case R_ARM_TLS_IE32:
   case R_ARM_TLS_LDM32:
   case R_ARM_TLS_LDO32:
   case R_ARM_TLS_LE32:
   case R_ARM_TLS_TPOFF32:

lld/trunk/test/ELF/arm-pie-relative.s

+// RUN: llvm-mc -filetype=obj -triple=armv7a-none-linux-gnueabi %s -o %t
+// RUN: ld.lld %t --pie -o %t2
+// RUN: llvm-readobj -r %t2 | FileCheck %s
+// RUN: llvm-objdump -s %t2 | FileCheck %s --check-prefix=GOT
+// REQUIRES: arm
+
+// Test that a R_ARM_GOT_BREL relocation with PIE results in a R_ARM_RELATIVE
+// dynamic relocation
+ .syntax unified
+ .text
+ .global _start
+_start:
+ .word sym(GOT)
+
+ .data
+ .global sym
+sym:
+ .word 0
+
+// CHECK:      Relocations [
+// CHECK-NEXT:   Section (4) .rel.dyn {
+// CHECK-NEXT:     0x2058 R_ARM_RELATIVE
+
+// GOT: Contents of section .got:
+// GOT-NEXT:  2058 00300000