Refactored, improved test, and addressed reviewers.

Author: paschalis-mpeis

bolt/include/bolt/Core/MCPlusBuilder.h

@@ -2034,7 +2034,10 @@ class MCPlusBuilder {
     return InstructionListType();
   }
 
-  virtual InstructionListType createDummyReturnFunction(MCContext *Ctx) const {
+  /// Returns a function body that contains only a return instruction. An
+  /// example usage is a workaround for the '__bolt_fini_trampoline' of
+  // Instrumentation.
+  virtual InstructionListType createDummyReturn(MCContext *Ctx) const {
     llvm_unreachable("not implemented");
     return InstructionListType();
   }

bolt/lib/Passes/Instrumentation.cpp

@@ -755,7 +755,7 @@ void Instrumentation::createAuxiliaryFunctions(BinaryContext &BC) {
       // with unknown symbol in runtime library. E.g. for static PIE
       // executable
       createSimpleFunction("__bolt_fini_trampoline",
-                           BC.MIB->createDummyReturnFunction(BC.Ctx.get()));
+                           BC.MIB->createDummyReturn(BC.Ctx.get()));
     }
   }
 }

bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp

@@ -1607,7 +1607,7 @@ class AArch64MCPlusBuilder : public MCPlusBuilder {
     return Instrs;
   }
 
-  InstructionListType createDummyReturnFunction(MCContext *Ctx) const override {
+  InstructionListType createDummyReturn(MCContext *Ctx) const override {
     InstructionListType Insts(1);
     createReturn(Insts[0]);
     return Insts;

bolt/lib/Target/X86/X86MCPlusBuilder.cpp

@@ -3271,7 +3271,7 @@ class X86MCPlusBuilder : public MCPlusBuilder {
     return Insts;
   }
 
-  InstructionListType createDummyReturnFunction(MCContext *Ctx) const override {
+  InstructionListType createDummyReturn(MCContext *Ctx) const override {
     InstructionListType Insts(1);
     createReturn(Insts[0]);
     return Insts;

bolt/test/AArch64/dummy-return.test

@@ -1,10 +1,13 @@
-// Tests that AArch64 is able to instrument static binaries in relocation mode.
+// Tests that AArch64 is able to instrument static binaries in relocation mode,
+// by checking that '__bolt_fini_trampoline' is generated and contains a 'ret'
+// instruction.
 
 REQUIRES: system-linux
 
 RUN: %clang %p/../Inputs/main.c -o %t -Wl,-q -static
 RUN: llvm-bolt -instrument -instrumentation-sleep-time=1 %t -o %t.instr 2>&1 | FileCheck %s
-RUN: llvm-nm -n %t.instr | FileCheck %s -check-prefix=CHECK-SYM
+RUN: llvm-objdump --disassemble-symbols=__bolt_fini_trampoline %t.instr -D | FileCheck %s -check-prefix=CHECK-ASM
 
 CHECK: BOLT-INFO: output linked against instrumentation runtime library
-CHECK-SYM: __bolt_fini_trampoline
+CHECK-ASM: <__bolt_fini_trampoline>:
+CHECK-ASM-NEXT: ret

bolt/test/Inputs/main.c

@@ -1,3 +1,3 @@
-// dummy function just for emitting relocations  to the linker.
+// dummy function just for emitting relocations to the linker.
 int foo() { return 0; }
 int main(int argc, char **argv) { return foo() + 1; }