[WebKit checkers] Treat asm brk as trivial

[rniwa]

Like other functions which results in abort, treat asm brk instruction as trivial.

[llvmbot]

@llvm/pr-subscribers-clang

@llvm/pr-subscribers-clang-static-analyzer-1

Author: Ryosuke Niwa (rniwa)

Changes

Like other functions which results in abort, treat asm brk instruction as trivial.

---

Full diff: https://github.com/llvm/llvm-project/pull/155046.diff

2 Files Affected:

• (modified) clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp (+7)
• (added) clang/test/Analysis/Checkers/WebKit/trivial-code-check-asm-brk.cpp (+22)

diff --git a/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp b/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp
index 36c12582a5787..93ffc58b1055e 100644
--- a/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp
@@ -666,6 +666,13 @@ class TrivialFunctionAnalysisVisitor
     return IsFunctionTrivial(Callee);
   }
 
+  bool VisitGCCAsmStmt(const GCCAsmStmt *AS) {
+    auto *Asm = AS->getAsmString();
+    if (!Asm)
+      return false;
+    return Asm->getString() == "brk #0xc471";
+  }
+
   bool
   VisitSubstNonTypeTemplateParmExpr(const SubstNonTypeTemplateParmExpr *E) {
     // Non-type template paramter is compile time constant and trivial.
diff --git a/clang/test/Analysis/Checkers/WebKit/trivial-code-check-asm-brk.cpp b/clang/test/Analysis/Checkers/WebKit/trivial-code-check-asm-brk.cpp
new file mode 100644
index 0000000000000..de98c77eb7347
--- /dev/null
+++ b/clang/test/Analysis/Checkers/WebKit/trivial-code-check-asm-brk.cpp
@@ -0,0 +1,22 @@
+// RUN: %clang_analyze_cc1 -triple arm-darwin -analyzer-checker=alpha.webkit.UncountedCallArgsChecker -verify %s
+// expected-no-diagnostics
+
+void crash()
+{
+  __asm__ volatile ("brk #0xc471");
+  __builtin_unreachable();
+}
+
+class SomeObj {
+public:
+  void ref();
+  void deref();
+
+  void someWork() { crash(); }
+};
+
+SomeObj* provide();
+
+void doSomeWork() {
+  provide()->someWork();
+}

[ojhunt]

does this need to be restricted to a specific brk constant, and should it include int3, and similar?

I guess it's unlikely as whitespace is usually present only in multiline asm but is it worth considering stripping white space?

[rniwa]

It could be other kinds of brk as long as it triggers a crash.

[rniwa]

We could consider stripping whitespace but it's probably not necessary for a WebKit specific checker since we would never add random whitespace around brk. Having said that, in long term, a better solution would be to provide a way to annotate that a function causes the program to terminate.

[t-rasmud]

LGTM!