[BOLT] Disallow Instrumentation mode for pac-ret binaries

- add unittest to cover this check

Author: bgergely0

bolt/lib/Rewrite/RewriteInstance.cpp

@@ -700,6 +700,12 @@ Error RewriteInstance::run() {
   adjustCommandLineOptions();
   discoverFileObjects();
 
+  if (opts::Instrument && opts::AllowPacret) {
+    BC->errs() << "BOLT-ERROR: Instrumenting binaries with pac-ret hardening "
+                  "is not supported.\n";
+    exit(1);
+  }
+
   if (opts::Instrument && !BC->IsStaticExecutable)
     if (Error E = discoverRtFiniAddress())
       return E;

bolt/test/AArch64/pacret-instrument-flags.s

@@ -0,0 +1,40 @@
+# Instrumenting binaries with pac-ret hardening is not supported.
+# This test makes sure that BOLT will fail when ran with both the
+# --allow-experimental-pacret and --instrument flags.
+
+# RUN: llvm-mc -filetype=obj -triple aarch64-unknown-unknown %s -o %t.o
+# RUN: %clang %cflags  %t.o -o %t.exe -Wl,-q
+
+# RUN: not llvm-bolt %t.exe -o %t.bolt --allow-experimental-pacret --instrument 2>&1 | FileCheck %s
+
+# CHECK: BOLT-ERROR: Instrumenting binaries with pac-ret hardening is not supported.
+
+	.text
+	.globl	foo
+	.p2align	2
+	.type	foo,@function
+foo:
+	.cfi_startproc
+	hint	#25
+	.cfi_negate_ra_state
+	sub	sp, sp, #16
+	stp	x29, x30, [sp, #16]             // 16-byte Folded Spill
+	.cfi_def_cfa_offset 16
+	str	w0, [sp, #12]
+	ldr	w8, [sp, #12]
+	add	w0, w8, #1
+	ldp	x29, x30, [sp, #16]             // 16-byte Folded Reload
+	add	sp, sp, #16
+	hint	#29
+	.cfi_negate_ra_state
+	ret
+.Lfunc_end1:
+	.size	foo, .Lfunc_end1-foo
+	.cfi_endproc
+
+	.global _start
+	.type _start, %function
+_start:
+	b foo
+
+.reloc 0, R_AARCH64_NONE