[BOLT] Issue error on unclaimed PC-relative relocation (llvm#166098)

Replace assert with an error and improve the report when unclaimed
PC-relative relocation is left in strict mode.

Author: maksfb

bolt/lib/Core/BinaryContext.cpp

@@ -778,13 +778,17 @@ void BinaryContext::populateJumpTables() {
   }
 
   if (opts::StrictMode && DataPCRelocations.size()) {
-    LLVM_DEBUG({
-      dbgs() << DataPCRelocations.size()
-             << " unclaimed PC-relative relocations left in data:\n";
-      for (uint64_t Reloc : DataPCRelocations)
-        dbgs() << Twine::utohexstr(Reloc) << '\n';
-    });
-    assert(0 && "unclaimed PC-relative relocations left in data\n");
+    this->errs() << "BOLT-ERROR: " << DataPCRelocations.size()
+                 << " unclaimed PC-relative relocation(s) left in data";
+    if (opts::Verbosity) {
+      this->errs() << ":\n";
+      for (uint64_t RelocOffset : DataPCRelocations)
+        this->errs() << "  @0x" << Twine::utohexstr(RelocOffset) << '\n';
+    } else {
+      this->errs() << ". Re-run with -v=1 to see the list\n";
+    }
+    this->errs() << "BOLT-ERROR: unable to proceed with --strict\n";
+    exit(1);
   }
   clearList(DataPCRelocations);
 }

bolt/test/X86/unclaimed-pc-rel.s

@@ -0,0 +1,24 @@
+## Check that unclaimed PC-relative relocation from data to code is detected
+## and reported to the user.
+
+# REQUIRES: system-linux
+
+# RUN: %clang %cflags -no-pie %s -o %t.exe -Wl,-q -nostartfiles
+# RUN: not llvm-bolt %t.exe -o %t.bolt --strict 2>&1 | FileCheck %s
+
+# CHECK: BOLT-ERROR: 1 unclaimed PC-relative relocation(s) left in data
+
+  .text
+  .globl _start
+  .type _start, %function
+_start:
+  movl $42, %eax
+.L0:
+  ret
+  .size _start, .-_start
+
+## Force relocation mode.
+  .reloc 0, R_X86_64_NONE
+
+  .section .rodata
+  .long .L0-.