[clang] [Clang][Sema] Fix crash with asm goto and OpenMP pragma (PR #179368)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: None (nataliakokoromyti)

<details>
<summary>Changes</summary>

We were getting a segfault when using asm goto with an undeclared label inside an OpenMP pragma (see issue #<!-- -->179238). The issue was that when you have an undeclared label in an OpenMP scope, Target (which is a LabelDecl*) can be null. The code was just assuming it was always valid and dereferencing it without checking. Just adding a null check before using Target fixes it. Still reports the errors (undeclared label, invalid jump, etc.) but doesn't segfault.

---
Full diff: https://github.com/llvm/llvm-project/pull/179368.diff


2 Files Affected:

- (modified) clang/lib/Sema/JumpDiagnostics.cpp (+2-1) 
- (added) clang/test/Sema/openmp-asm-goto-crash.c (+11) 


``````````diff
diff --git a/clang/lib/Sema/JumpDiagnostics.cpp b/clang/lib/Sema/JumpDiagnostics.cpp
index 2c45de69e7cdf..f7bc8dea5fa75 100644
--- a/clang/lib/Sema/JumpDiagnostics.cpp
+++ b/clang/lib/Sema/JumpDiagnostics.cpp
@@ -916,7 +916,8 @@ static void DiagnoseIndirectOrAsmJumpStmt(Sema &S, Stmt *Jump,
   bool IsAsmGoto = isa<GCCAsmStmt>(Jump);
   S.Diag(Jump->getBeginLoc(), diag::err_indirect_goto_in_protected_scope)
       << IsAsmGoto;
-  S.Diag(Target->getStmt()->getIdentLoc(), diag::note_indirect_goto_target)
+  if (Target && Target->getStmt())
+    S.Diag(Target->getStmt()->getIdentLoc(), diag::note_indirect_goto_target)
       << IsAsmGoto;
   Diagnosed = true;
 }
diff --git a/clang/test/Sema/openmp-asm-goto-crash.c b/clang/test/Sema/openmp-asm-goto-crash.c
new file mode 100644
index 0000000000000..7429573b4c2db
--- /dev/null
+++ b/clang/test/Sema/openmp-asm-goto-crash.c
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -fopenmp -fsyntax-only -verify -triple x86_64-unknown-linux-gnu %s
+
+int test_asm_goto_undeclared_label() {
+#pragma omp assume
+  __asm__ goto("" : : : : undefined_label); // expected-error {{use of undeclared label 'undefined_label'}} \
+                                             // expected-error {{cannot jump from this asm goto statement to one of its possible targets}} \
+                                             // expected-note {{jump exits scope of OpenMP structured block}}
+  int x = 1;
+undefined_label:
+  return x;
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/179368