ELF: Add support for R_AARCH64_PATCHINST relocation type.

lld/ELF/Arch/AArch64.cpp

@@ -154,6 +154,12 @@ RelExpr AArch64::getRelExpr(RelType type, const Symbol &s,
   case R_AARCH64_MOVW_UABS_G2_NC:
   case R_AARCH64_MOVW_UABS_G3:
     return R_ABS;
+  case R_AARCH64_PATCHINST:
+    if (!isAbsolute(s))
+      Err(ctx) << getErrorLoc(ctx, loc)
+               << "R_AARCH64_PATCHINST relocation against non-absolute symbol "
+               << &s;
+    return R_ABS;
   case R_AARCH64_AUTH_ABS64:
     return RE_AARCH64_AUTH;
   case R_AARCH64_TLSDESC_ADR_PAGE21:
@@ -506,6 +512,12 @@ void AArch64::relocate(uint8_t *loc, const Relocation &rel,
     checkIntUInt(ctx, loc, val, 32, rel);
     write32(ctx, loc, val);
     break;
+  case R_AARCH64_PATCHINST:
+    if (!rel.sym->isUndefined()) {
+      checkUInt(ctx, loc, val, 32, rel);
+      write32le(loc, val);
+    }
+    break;
   case R_AARCH64_PLT32:
   case R_AARCH64_GOTPCREL32:
     checkInt(ctx, loc, val, 32, rel);

lld/ELF/Relocations.cpp

@@ -176,7 +176,7 @@ static RelType getMipsPairType(RelType type, bool isLocal) {
 
 // True if non-preemptable symbol always has the same value regardless of where
 // the DSO is loaded.
-static bool isAbsolute(const Symbol &sym) {
+bool elf::isAbsolute(const Symbol &sym) {
   if (sym.isUndefined())
     return true;
   if (const auto *dr = dyn_cast<Defined>(&sym))

lld/ELF/Relocations.h

@@ -165,6 +165,8 @@ void addGotEntry(Ctx &ctx, Symbol &sym);
 void hexagonTLSSymbolUpdate(Ctx &ctx);
 bool hexagonNeedsTLSSymbol(ArrayRef<OutputSection *> outputSections);
 
+bool isAbsolute(const Symbol &sym);
+
 class ThunkSection;
 class Thunk;
 class InputSectionDescription;

lld/test/ELF/aarch64-patchinst.s

@@ -0,0 +1,87 @@
+# RUN: rm -rf %t && split-file %s %t
+# RUN: llvm-mc -filetype=obj -triple=aarch64 %t/use.s -o %t/use-le.o
+# RUN: llvm-mc -filetype=obj -triple=aarch64 %t/def.s -o %t/def-le.o
+# RUN: llvm-mc -filetype=obj -triple=aarch64 %t/rel.s -o %t/rel-le.o
+
+## Deactivation symbol used without being defined: instruction emitted as usual.
+# RUN: ld.lld -o %t/undef-le %t/use-le.o --emit-relocs
+# RUN: llvm-objdump -r %t/undef-le | FileCheck --check-prefix=RELOC %s
+# RUN: llvm-objdump -d %t/undef-le | FileCheck --check-prefix=UNDEF %s
+# RUN: ld.lld -pie -o %t/undef-le %t/use-le.o --emit-relocs
+# RUN: llvm-objdump -r %t/undef-le | FileCheck --check-prefix=RELOC %s
+# RUN: llvm-objdump -d %t/undef-le | FileCheck --check-prefix=UNDEF %s
+
+## Deactivation symbol defined: instructions overwritten with NOPs.
+# RUN: ld.lld -o %t/def-le %t/use-le.o %t/def-le.o --emit-relocs
+# RUN: llvm-objdump -r %t/def-le | FileCheck --check-prefix=RELOC %s
+# RUN: llvm-objdump -d %t/def-le | FileCheck --check-prefix=DEF %s
+# RUN: ld.lld -pie -o %t/def-le %t/use-le.o %t/def-le.o --emit-relocs
+# RUN: llvm-objdump -r %t/def-le | FileCheck --check-prefix=RELOC %s
+# RUN: llvm-objdump -d %t/def-le | FileCheck --check-prefix=DEF %s
+
+## Relocation pointing to a non-SHN_UNDEF non-SHN_ABS symbol is an error.
+# RUN: not ld.lld -o %t/rel-le %t/use-le.o %t/rel-le.o 2>&1 | FileCheck --check-prefix=ERROR %s
+# RUN: not ld.lld -pie -o %t/rel-le %t/use-le.o %t/rel-le.o 2>&1 | FileCheck --check-prefix=ERROR %s
+
+## Behavior unchanged by endianness: relocation always written as little endian.
+# RUN: llvm-mc -filetype=obj -triple=aarch64_be %t/use.s -o %t/use-be.o
+# RUN: llvm-mc -filetype=obj -triple=aarch64_be %t/def.s -o %t/def-be.o
+# RUN: llvm-mc -filetype=obj -triple=aarch64_be %t/rel.s -o %t/rel-be.o
+# RUN: ld.lld -o %t/undef-be %t/use-be.o --emit-relocs
+# RUN: llvm-objdump -r %t/undef-be | FileCheck --check-prefix=RELOC %s
+# RUN: llvm-objdump -d %t/undef-be | FileCheck --check-prefix=UNDEF %s
+# RUN: ld.lld -pie -o %t/undef-be %t/use-be.o --emit-relocs
+# RUN: llvm-objdump -r %t/undef-be | FileCheck --check-prefix=RELOC %s
+# RUN: llvm-objdump -d %t/undef-be | FileCheck --check-prefix=UNDEF %s
+# RUN: ld.lld -o %t/def-be %t/use-be.o %t/def-be.o --emit-relocs
+# RUN: llvm-objdump -r %t/def-be | FileCheck --check-prefix=RELOC %s
+# RUN: llvm-objdump -d %t/def-be | FileCheck --check-prefix=DEF %s
+# RUN: ld.lld -pie -o %t/def-be %t/use-be.o %t/def-be.o --emit-relocs
+# RUN: llvm-objdump -r %t/def-be | FileCheck --check-prefix=RELOC %s
+# RUN: llvm-objdump -d %t/def-be | FileCheck --check-prefix=DEF %s
+# RUN: not ld.lld -o %t/rel-be %t/use-be.o %t/rel-be.o 2>&1 | FileCheck --check-prefix=ERROR %s
+# RUN: not ld.lld -pie -o %t/rel-be %t/use-be.o %t/rel-be.o 2>&1 | FileCheck --check-prefix=ERROR %s
+
+# RELOC:      R_AARCH64_JUMP26
+# RELOC-NEXT: R_AARCH64_PATCHINST ds
+# RELOC-NEXT: R_AARCH64_PATCHINST ds
+# RELOC-NEXT: R_AARCH64_PATCHINST ds0+0xd503201f
+
+#--- use.s
+.weak ds
+.weak ds0
+# This instruction has a single relocation: the DS relocation.
+# UNDEF: add x0, x1, x2
+# DEF: nop
+# ERROR: R_AARCH64_PATCHINST relocation against non-absolute symbol ds
+.reloc ., R_AARCH64_PATCHINST, ds
+add x0, x1, x2
+# This instruction has two relocations: the DS relocation and the JUMP26 to f1.
+# Make sure that the DS relocation takes precedence.
+.reloc ., R_AARCH64_PATCHINST, ds
+# UNDEF: b {{.*}} <f1>
+# DEF: nop
+# ERROR: R_AARCH64_PATCHINST relocation against non-absolute symbol ds
+b f1
+# Alternative representation: instruction opcode stored in addend.
+# UNDEF: add x3, x4, x5
+# DEF: nop
+# ERROR: R_AARCH64_PATCHINST relocation against non-absolute symbol ds0
+.reloc ., R_AARCH64_PATCHINST, ds0 + 0xd503201f
+add x3, x4, x5
+
+.section .text.f1,"ax",@progbits
+f1:
+ret
+
+#--- def.s
+.globl ds
+ds = 0xd503201f
+.globl ds0
+ds0 = 0
+
+#--- rel.s
+.globl ds
+ds:
+.globl ds0
+ds0: