[BOLT][AArch64] Symbolize ADRP after relaxation

bolt/lib/Target/AArch64/AArch64MCSymbolizer.cpp

@@ -125,15 +125,39 @@ AArch64MCSymbolizer::adjustRelocation(const Relocation &Rel,
     // instruction pairs and will perform necessary adjustments.
     ErrorOr<uint64_t> SymbolValue = BC.getSymbolValue(*Rel.Symbol);
     assert(SymbolValue && "Symbol value should be set");
-    (void)SymbolValue;
-
-    AdjustedRel.Symbol = BC.registerNameAtAddress("__BOLT_got_zero", 0, 0, 0);
-    AdjustedRel.Addend = Rel.Value;
+    const uint64_t SymbolPageAddr = *SymbolValue & ~0xfffULL;
+
+    // Check if defined symbol and GOT are on the same page. If they are not,
+    // disambiguate the operand.
+    if (BC.MIB->isADRP(Inst) && Rel.Addend == 0 &&
+        SymbolPageAddr == Rel.Value &&
+        !isPageAddressValidForGOT(SymbolPageAddr)) {
+      AdjustedRel.Type = ELF::R_AARCH64_ADR_PREL_PG_HI21;
+    } else {
+      AdjustedRel.Symbol = BC.registerNameAtAddress("__BOLT_got_zero", 0, 0, 0);
+      AdjustedRel.Addend = Rel.Value;
+    }
   }
 
   return AdjustedRel;
 }
 
+bool AArch64MCSymbolizer::isPageAddressValidForGOT(uint64_t PageAddress) const {
+  assert(!(PageAddress & 0xfffULL) && "Page address not aligned at 4KB");
+
+  ErrorOr<BinarySection &> GOT =
+      Function.getBinaryContext().getUniqueSectionByName(".got");
+  if (!GOT || !GOT->getSize())
+    return false;
+
+  const uint64_t GOTFirstPageAddress = GOT->getAddress() & ~0xfffULL;
+  const uint64_t GOTLastPageAddress =
+      (GOT->getAddress() + GOT->getSize() - 1) & ~0xfffULL;
+
+  return PageAddress >= GOTFirstPageAddress &&
+         PageAddress <= GOTLastPageAddress;
+}
+
 void AArch64MCSymbolizer::tryAddingPcLoadReferenceComment(raw_ostream &CStream,
                                                           int64_t Value,
                                                           uint64_t Address) {}

bolt/lib/Target/AArch64/AArch64MCSymbolizer.h

@@ -28,6 +28,9 @@ class AArch64MCSymbolizer : public MCSymbolizer {
   std::optional<Relocation> adjustRelocation(const Relocation &Rel,
                                              const MCInst &Inst) const;
 
+  /// Return true if \p PageAddress is a valid page address for .got section.
+  bool isPageAddressValidForGOT(uint64_t PageAddress) const;
+
 public:
   AArch64MCSymbolizer(BinaryFunction &Function, bool CreateNewSymbols = true)
       : MCSymbolizer(*Function.getBinaryContext().Ctx.get(), nullptr),

bolt/test/AArch64/got-load-symbolization.s

@@ -0,0 +1,100 @@
+## Check that BOLT symbolizer properly handles loads from GOT, including
+## instruction sequences changed/relaxed by the linker.
+
+# RUN: split-file %s %t
+
+# RUN: llvm-mc -filetype=obj -triple aarch64-unknown-unknown %t/main.s \
+# RUN:   -o %t/main.o
+# RUN: llvm-mc -filetype=obj -triple aarch64-unknown-unknown %t/near.s \
+# RUN:   -o %t/near.o
+# RUN: llvm-mc -filetype=obj -triple aarch64-unknown-unknown %t/far.s \
+# RUN:   -o %t/far.o
+# RUN: %clang %cflags %t/main.o %t/near.o %t/far.o -o %t/main.exe -Wl,-q -static
+# RUN: llvm-bolt %t/main.exe -o %t/main.bolt --keep-nops --print-disasm \
+# RUN:   --print-only=_start | FileCheck %s
+
+#--- main.s
+
+	.text
+	.globl _start
+	.p2align        2
+	.type _start, @function
+# CHECK-LABEL: _start
+_start:
+
+## Function address load relaxable into nop+adr.
+# CHECK: 			nop
+# CHECK-NEXT: adr x0, near
+	adrp    x0, :got:near
+	ldr     x0, [x0, :got_lo12:near]
+
+## Function address load relaxable into adrp+add.
+# CHECK-NEXT: adrp x1, far
+# CHECK-NEXT: add  x1, x1, :lo12:far
+	adrp    x1, :got:far
+	ldr     x1, [x1, :got_lo12:far]
+
+## Non-relaxable due to the instruction in-between.
+# CHECK-NEXT: adrp x2, __BOLT_got_zero
+# CHECK-NEXT: nop
+# CHECK-NEXT: ldr  x2, [x2, :lo12:__BOLT_got_zero{{.*}}]
+	adrp    x2, :got:near
+	nop
+	ldr     x2, [x2, :got_lo12:near]
+
+## Load data object with local visibility. Relaxable into adrp+add.
+# CHECK-NEXT: adrp x3, "local_far_data/1"
+# CHECK-NEXT: add  x3, x3, :lo12:"local_far_data/1"
+  adrp    x3, :got:local_far_data
+  ldr     x3, [x3, :got_lo12:local_far_data]
+
+## Global data reference relaxable into adrp+add.
+# CHECK-NEXT: adrp x4, far_data
+# CHECK-NEXT: add  x4, x4, :lo12:far_data
+  adrp    x4, :got:far_data
+  ldr     x4, [x4, :got_lo12:far_data]
+
+	ret
+	.size _start, .-_start
+
+.weak near
+.weak far
+.weak far_data
+
+## Data object separated by more than 1MB from _start.
+  .data
+  .type local_far_data, @object
+local_far_data:
+  .xword 0
+.size   local_far_data, .-local_far_data
+
+#--- near.s
+
+	.text
+	.globl near
+	.type near, @function
+near:
+  ret
+.size   near, .-near
+
+#--- far.s
+
+  .text
+
+## Insert 1MB of empty space to make objects after it unreachable by adr
+## instructions in _start.
+  .space 0x100000
+
+	.globl far
+	.type far, @function
+far:
+  ret
+.size   far, .-far
+
+  .data
+  .globl far_data
+  .type far_data, @object
+far_data:
+  .xword 0
+.size   far_data, .-far_data
+