[lld] d21fb06 - [lld][ELF] Allow Arm PC-relative relocations in PIC links (#77304)

[via llvm-commits]

Author: Eleanor Bonnici
Date: 2024-01-11T16:49:14Z
New Revision: d21fb06a6e36048e6729c51c351ff8c4055e8381

URL: https://github.com/llvm/llvm-project/commit/d21fb06a6e36048e6729c51c351ff8c4055e8381
DIFF: https://github.com/llvm/llvm-project/commit/d21fb06a6e36048e6729c51c351ff8c4055e8381.diff

LOG: [lld][ELF] Allow Arm PC-relative relocations in PIC links (#77304)

The relocations that map to R_ARM_PCA are equivalent to R_PC. They are
PC-relative and safe to use in shared libraries, but have a different
relocation code as they are evaluated differently. Now that LLVM may
generate these relocations in object files, they may occur in
shared libraries or position-independent executables.

Added: 
    

Modified: 
    lld/ELF/Relocations.cpp
    lld/test/ELF/arm-adr.s

Removed: 
    


################################################################################
diff  --git a/lld/ELF/Relocations.cpp b/lld/ELF/Relocations.cpp
index 20eb02b8798447..af974d0f90e1d2 100644
--- a/lld/ELF/Relocations.cpp
+++ b/lld/ELF/Relocations.cpp
@@ -210,10 +210,10 @@ bool lld::elf::needsGot(RelExpr expr) {
 // True if this expression is of the form Sym - X, where X is a position in the
 // file (PC, or GOT for example).
 static bool isRelExpr(RelExpr expr) {
-  return oneof<R_PC, R_GOTREL, R_GOTPLTREL, R_MIPS_GOTREL, R_PPC64_CALL,
-               R_PPC64_RELAX_TOC, R_AARCH64_PAGE_PC, R_RELAX_GOT_PC,
-               R_RISCV_PC_INDIRECT, R_PPC64_RELAX_GOT_PC, R_LOONGARCH_PAGE_PC>(
-      expr);
+  return oneof<R_PC, R_GOTREL, R_GOTPLTREL, R_ARM_PCA, R_MIPS_GOTREL,
+               R_PPC64_CALL, R_PPC64_RELAX_TOC, R_AARCH64_PAGE_PC,
+               R_RELAX_GOT_PC, R_RISCV_PC_INDIRECT, R_PPC64_RELAX_GOT_PC,
+               R_LOONGARCH_PAGE_PC>(expr);
 }
 
 static RelExpr toPlt(RelExpr expr) {

diff  --git a/lld/test/ELF/arm-adr.s b/lld/test/ELF/arm-adr.s
index 05e8cc2f92db3e..fee78f97a12e85 100644
--- a/lld/test/ELF/arm-adr.s
+++ b/lld/test/ELF/arm-adr.s
@@ -1,6 +1,8 @@
 // REQUIRES: arm
 // RUN: llvm-mc --triple=armv7a-none-eabi --arm-add-build-attributes -filetype=obj -o %t.o %s
 // RUN: ld.lld %t.o -o %t
+/// R_ARM_ALU_PC_G0 referencing a non-preemptible symbol can be used in PIC links.
+// RUN: ld.lld %t.o --shared -o /dev/null
 // RUN: llvm-objdump -d --no-show-raw-insn --triple=armv7a-none-eabi %t | FileCheck %s
 
 /// Test the short range cases of R_ARM_ALU_PC_G0. The range of the instruction