[BOLT] Skip _init; avoiding GOT breakage for static binaries

bolt/lib/Rewrite/RewriteInstance.cpp

@@ -2927,6 +2927,23 @@ void RewriteInstance::handleRelocation(const SectionRef &RelocatedSection,
     LLVM_DEBUG(dbgs() << "BOLT-DEBUG: ignoring relocation from data to data\n");
 }
 
+static BinaryFunction *getInitFunctionIfStaticBinary(BinaryContext &BC) {
+  // Workaround for https://github.com/llvm/llvm-project/issues/100096
+  // ("[BOLT] GOT array pointer incorrectly rewritten"). In aarch64
+  // static glibc binaries, the .init section's _init function pointer can
+  // alias with a data pointer for the end of an array. GOT rewriting
+  // currently can't detect this and updates the data pointer to the
+  // moved _init, causing a runtime crash. Skipping _init on the other
+  // hand should be harmless.
+  if (!BC.IsStaticExecutable)
+    return nullptr;
+  const BinaryData *BD = BC.getBinaryDataByName("_init");
+  if (!BD || BD->getSectionName() != ".init")
+    return nullptr;
+  LLVM_DEBUG(dbgs() << "BOLT-DEBUG: skip _init in for GOT workaround.\n");
+  return BC.getBinaryFunctionAtAddress(BD->getAddress());
+}
+
 void RewriteInstance::selectFunctionsToProcess() {
   // Extend the list of functions to process or skip from a file.
   auto populateFunctionNames = [](cl::opt<std::string> &FunctionNamesFile,
@@ -3047,6 +3064,9 @@ void RewriteInstance::selectFunctionsToProcess() {
     return true;
   };
 
+  if (BinaryFunction *Init = getInitFunctionIfStaticBinary(*BC))
+    Init->setIgnored();
+
   for (auto &BFI : BC->getBinaryFunctions()) {
     BinaryFunction &Function = BFI.second;
 

bolt/test/AArch64/check-init-not-moved.s

@@ -0,0 +1,43 @@
+# Regression test for https://github.com/llvm/llvm-project/issues/100096
+# static glibc binaries crash on startup because _init is moved and
+# shares its address with an array end pointer. The GOT rewriting can't
+# tell the two pointers apart and incorrectly updates the _array_end
+# address. Test checks that _init is not moved.
+
+# RUN: llvm-mc -filetype=obj -triple aarch64-unknown-unknown %s -o %t.o
+# RUN: %clang %cflags %t.o -o %t.exe -Wl,-q -static -Wl,--section-start=.data=0x1000 -Wl,--section-start=.init=0x1004
+# RUN: llvm-bolt %t.exe -o %t.bolt
+# RUN: llvm-nm %t.exe | FileCheck --check-prefix=CHECK-ORIGINAL %s
+# RUN: llvm-nm %t.bolt | FileCheck --check-prefix=CHECK-BOLTED %s
+
+.section .data
+.globl _array_end
+_array_start:
+    .word 0x0
+
+_array_end:
+.section .init,"ax",@progbits
+.globl _init
+
+# Check that bolt doesn't move _init.
+#
+# CHECK-ORIGINAL: 0000000000001004 T _init
+# CHECK-BOLTED:   0000000000001004 T _init
+_init:
+    ret
+
+.section .text,"ax",@progbits
+.globl _start
+
+# Check that bolt is moving some other functions.
+#
+# CHECK-ORIGINAL:   0000000000001008 T _start
+# CHECK-BOLTED-NOT: 0000000000001008 T _start
+_start:
+    bl _init
+    adrp x0, #:got:_array_end
+    ldr x0, [x0, #:gotpage_lo15:_array_end]
+    adrp x0, #:got:_init
+    ldr x0, [x0, #:gotpage_lo15:_init]
+    ret
+