From 963d19d86cca708957055f3072cbe8473c8e52e3 Mon Sep 17 00:00:00 2001
From: xiongzhou4 <xiongzhou4@huawei.com>
Date: Thu, 15 Jun 2023 20:34:42 +0800
Subject: [PATCH] [Backport] [BOLT] [AArch64] Handle data at the beginning of a
 function when disassembling and building CFG.

---
 bolt/src/BinaryFunction.cpp          | 11 +++++++----
 bolt/src/BinaryFunction.h            |  9 +++++++++
 bolt/src/Exceptions.cpp              |  2 +-
 bolt/test/AArch64/data-at-0-offset.c | 17 +++++++++++++++++
 4 files changed, 34 insertions(+), 5 deletions(-)
 create mode 100644 bolt/test/AArch64/data-at-0-offset.c

diff --git a/bolt/src/BinaryFunction.cpp b/bolt/src/BinaryFunction.cpp
index 9414b83ad..93de63d3f 100644
--- a/bolt/src/BinaryFunction.cpp
+++ b/bolt/src/BinaryFunction.cpp
@@ -1445,6 +1445,9 @@ add_instruction:
     addInstruction(Offset, std::move(Instruction));
   }
 
+  if (uint64_t Offset = getFirstInstructionOffset())
+    Labels[Offset] = BC.Ctx->createNamedTempSymbol();
+
   clearList(Relocations);
 
   if (!IsSimple) {
@@ -1987,7 +1990,7 @@ bool BinaryFunction::buildCFG(MCPlusBuilder::AllocatorIdTy AllocatorId) {
     return false;
 
   assert(BasicBlocks.empty() && "basic block list should be empty");
-  assert((Labels.find(0) != Labels.end()) &&
+  assert((Labels.find(getFirstInstructionOffset()) != Labels.end()) &&
          "first instruction should always have a label");
 
   // Create basic blocks in the original layout order:
@@ -2087,9 +2090,9 @@ bool BinaryFunction::buildCFG(MCPlusBuilder::AllocatorIdTy AllocatorId) {
         updateOffset(LastInstrOffset);
       }
     }
-    if (Offset == 0) {
-      // Add associated CFI pseudos in the first offset (0)
-      addCFIPlaceholders(0, InsertBB);
+    if (Offset == getFirstInstructionOffset()) {
+      // Add associated CFI pseudos in the first offset.
+      addCFIPlaceholders(Offset, InsertBB);
     }
 
     const bool IsBlockEnd = MIB->isTerminator(Instr);
diff --git a/bolt/src/BinaryFunction.h b/bolt/src/BinaryFunction.h
index a824f3d58..3b435cfb3 100644
--- a/bolt/src/BinaryFunction.h
+++ b/bolt/src/BinaryFunction.h
@@ -967,6 +967,15 @@ public:
     return const_cast<BinaryFunction *>(this)->getInstructionAtOffset(Offset);
   }
 
+  /// Return offset for the first instruction. If there is data at the
+  /// beginning of a function then offset of the first instruction could
+  /// be different from 0.
+  uint64_t getFirstInstructionOffset() const {
+    if (Instructions.empty())
+      return 0;
+    return Instructions.begin()->first;
+  }
+
   /// Return jump table that covers a given \p Address in memory.
   JumpTable *getJumpTableContainingAddress(uint64_t Address) {
     auto JTI = JumpTables.upper_bound(Address);
diff --git a/bolt/src/Exceptions.cpp b/bolt/src/Exceptions.cpp
index f73054aa8..0a64e3fca 100644
--- a/bolt/src/Exceptions.cpp
+++ b/bolt/src/Exceptions.cpp
@@ -499,7 +499,7 @@ bool CFIReaderWriter::fillCFIInfoFor(BinaryFunction &Function) const {
   Optional<uint64_t> LSDA = CurFDE.getLSDAAddress();
   Function.setLSDAAddress(LSDA ? *LSDA : 0);
 
-  uint64_t Offset = 0;
+  uint64_t Offset = Function.getFirstInstructionOffset();
   uint64_t CodeAlignment = CurFDE.getLinkedCIE()->getCodeAlignmentFactor();
   uint64_t DataAlignment = CurFDE.getLinkedCIE()->getDataAlignmentFactor();
   if (CurFDE.getLinkedCIE()->getPersonalityAddress()) {
diff --git a/bolt/test/AArch64/data-at-0-offset.c b/bolt/test/AArch64/data-at-0-offset.c
new file mode 100644
index 000000000..e0c689a19
--- /dev/null
+++ b/bolt/test/AArch64/data-at-0-offset.c
@@ -0,0 +1,17 @@
+// RUN: %clang %cflags -O2 -fPIE -Wl,-q -pie  %s -o %t.exe
+// RUN: llvm-bolt %t.exe -o %t.bolt 2>&1 | FileCheck %s
+// CHECK-NOT: BOLT-WARNING: unable to disassemble instruction at offset
+
+void extra_space() {
+  asm volatile(".rept 256\n"
+               "    .byte 0xff\n"
+               ".endr\n");
+  return;
+}
+
+int main(int argc, char **argv) {
+  void (*fn)(void);
+  fn = extra_space + 256;
+  fn();
+  return 0;
+}
-- 
2.33.0