[BOLT] AArch64: Emit text objects

BOLT treats aarch64 objects located in text as empty functions with
contant islands. Emit them with at least 8-byte alignment to the new
text section.

Vladislav Khmelevsky,
Advanced Software Technology Lab, Huawei

Differential Revision: https://reviews.llvm.org/D122097

bolt/lib/Core/BinaryEmitter.cpp

@@ -277,7 +277,7 @@ void BinaryEmitter::emitFunctions() {
 }
 
 bool BinaryEmitter::emitFunction(BinaryFunction &Function, bool EmitColdPart) {
-  if (Function.size() == 0)
+  if (Function.size() == 0 && !Function.hasIslandsInfo())
     return false;
 
   if (Function.getState() == BinaryFunction::State::Empty)

bolt/lib/Passes/Aligner.cpp

@@ -172,6 +172,20 @@ void AlignerPass::runOnFunctions(BinaryContext &BC) {
     else
       alignMaxBytes(BF);
 
+    // Align objects that contains constant islands and no code
+    // to at least 8 bytes.
+    if (!BF.size() && BF.hasIslandsInfo()) {
+      const uint16_t Alignment = BF.getConstantIslandAlignment();
+      if (BF.getAlignment() < Alignment)
+        BF.setAlignment(Alignment);
+
+      if (BF.getMaxAlignmentBytes() < Alignment)
+        BF.setMaxAlignmentBytes(Alignment);
+
+      if (BF.getMaxColdAlignmentBytes() < Alignment)
+        BF.setMaxColdAlignmentBytes(Alignment);
+    }
+
     if (opts::AlignBlocks && !opts::PreserveBlocksAlignment)
       alignBlocks(BF, Emitter.MCE.get());
   };

bolt/test/AArch64/text-data.c

@@ -0,0 +1,22 @@
+// This test checks that the data object located in text section
+// is properly emitted in the new section.
+
+// RUN: %clang %cflags %s -o %t.exe -Wl,-q
+// RUN: llvm-bolt %t.exe -o %t.bolt -lite=0 -use-old-text=0
+// RUN: llvm-objdump -j .text -d --disassemble-symbols=arr %t.bolt | \
+// RUN:   FileCheck %s
+
+// CHECK: {{.*}} <arr>:
+
+#include <stdlib.h>
+
+typedef void (*FooPtr)();
+
+void exitOk() { exit(0); }
+
+__attribute__((section(".text"))) const FooPtr arr[] = {exitOk, NULL};
+
+int main() {
+  arr[0]();
+  return -1;
+}