[Lldb-commits] [lldb] [lldb] Allow forks to occur in expression evaluation (PR #184815)

[via lldb-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-lldb

Author: Philip DePetro (pdepetro)

<details>
<summary>Changes</summary>

@<!-- -->jimingham You had suggested to @<!-- -->clayborg that we should call DidFork(), DidVFork() and DidVForkDone() after a corresponding stop in expression evaluation. Those functions require parameters that are private to the specific child StopInfo class.  I went with reusing the existing StopInfo::PerformAction() virtual function, rather than create a new one just for this purpose.

---
Full diff: https://github.com/llvm/llvm-project/pull/184815.diff


5 Files Affected:

- (modified) lldb/include/lldb/Target/StopInfo.h (+1) 
- (modified) lldb/source/Target/ThreadPlanCallFunction.cpp (+15) 
- (added) lldb/test/API/commands/expression/expr-with-fork/Makefile (+4) 
- (added) lldb/test/API/commands/expression/expr-with-fork/TestExprWithFork.py (+49) 
- (added) lldb/test/API/commands/expression/expr-with-fork/main.cpp (+21) 


``````````diff
diff --git a/lldb/include/lldb/Target/StopInfo.h b/lldb/include/lldb/Target/StopInfo.h
index cdd6a6fbe6aa4..5c1f37edcbd3e 100644
--- a/lldb/include/lldb/Target/StopInfo.h
+++ b/lldb/include/lldb/Target/StopInfo.h
@@ -21,6 +21,7 @@ class StopInfo : public std::enable_shared_from_this<StopInfo> {
   friend class Process::ProcessEventData;
   friend class ThreadPlanBase;
   friend class ThreadPlanReverseContinue;
+  friend class ThreadPlanCallFunction;
 
 public:
   // Constructors and Destructors
diff --git a/lldb/source/Target/ThreadPlanCallFunction.cpp b/lldb/source/Target/ThreadPlanCallFunction.cpp
index 218111d4faf60..e555745754aab 100644
--- a/lldb/source/Target/ThreadPlanCallFunction.cpp
+++ b/lldb/source/Target/ThreadPlanCallFunction.cpp
@@ -284,6 +284,21 @@ bool ThreadPlanCallFunction::DoPlanExplainsStop(Event *event_ptr) {
   if (stop_reason == eStopReasonBreakpoint && BreakpointsExplainStop())
     return true;
 
+  if ((stop_reason == eStopReasonFork) ||
+      (stop_reason == eStopReasonVFork) ||
+      (stop_reason == eStopReasonVForkDone)) {
+    if (stop_reason == eStopReasonFork)
+      LLDB_LOGF(log, "ThreadPlanCallFunction::PlanExplainsStop hit a fork not stopping.");
+    else if (stop_reason == eStopReasonVFork)
+      LLDB_LOGF(log, "ThreadPlanCallFunction::PlanExplainsStop hit a vfork not stopping.");
+    else if (stop_reason == eStopReasonVForkDone)
+      LLDB_LOGF(log, "ThreadPlanCallFunction::PlanExplainsStop hit a vforkdone not stopping.");
+
+    m_real_stop_info_sp->PerformAction(event_ptr);
+    m_real_stop_info_sp->OverrideShouldStop(false);
+    return true;
+  }
+
   // One more quirk here.  If this event was from Halt interrupting the target,
   // then we should not consider ourselves complete.  Return true to
   // acknowledge the stop.
diff --git a/lldb/test/API/commands/expression/expr-with-fork/Makefile b/lldb/test/API/commands/expression/expr-with-fork/Makefile
new file mode 100644
index 0000000000000..f016d5b15d839
--- /dev/null
+++ b/lldb/test/API/commands/expression/expr-with-fork/Makefile
@@ -0,0 +1,4 @@
+CXX_SOURCES := main.cpp
+USE_SYSTEM_STDLIB := 1
+
+include Makefile.rules
diff --git a/lldb/test/API/commands/expression/expr-with-fork/TestExprWithFork.py b/lldb/test/API/commands/expression/expr-with-fork/TestExprWithFork.py
new file mode 100644
index 0000000000000..80ee288ee709a
--- /dev/null
+++ b/lldb/test/API/commands/expression/expr-with-fork/TestExprWithFork.py
@@ -0,0 +1,49 @@
+"""
+Test that expressions that call functions which fork
+can be evaluated successfully.
+
+This tests the ThreadPlanCallFunction handling of fork/vfork/vforkdone
+stop reasons, which should be silently resumed rather than causing the
+expression evaluation to fail.
+"""
+
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class ExprWithForkTestCase(TestBase):
+    NO_DEBUG_INFO_TESTCASE = True
+
+    @skipIfWindows
+    @add_test_categories(["fork"])
+    def test_expr_with_fork(self):
+        """Test that expression evaluation succeeds when the expression calls fork()."""
+        self.build()
+        (target, process, thread, bkpt) = lldbutil.run_to_source_breakpoint(
+            self, "// break here", lldb.SBFileSpec("main.cpp")
+        )
+
+        # Evaluate an expression that calls fork() inside a user function.
+        # The fork will generate a fork stop event which ThreadPlanCallFunction
+        # must handle transparently for the expression to complete.
+        self.expect_expr(
+            "fork_and_return(42, false)", result_type="int", result_value="42"
+        )
+
+    @skipIfWindows
+    @add_test_categories(["fork"])
+    def test_expr_with_vfork(self):
+        """Test that expression evaluation succeeds when the expression calls vfork()."""
+        self.build()
+        (target, process, thread, bkpt) = lldbutil.run_to_source_breakpoint(
+            self, "// break here", lldb.SBFileSpec("main.cpp")
+        )
+
+        # Evaluate an expression that calls fork() inside a user function.
+        # The fork will generate a fork stop event which ThreadPlanCallFunction
+        # must handle transparently for the expression to complete.
+        self.expect_expr(
+            "fork_and_return(42, true)", result_type="int", result_value="42"
+        )
diff --git a/lldb/test/API/commands/expression/expr-with-fork/main.cpp b/lldb/test/API/commands/expression/expr-with-fork/main.cpp
new file mode 100644
index 0000000000000..4e210df3d7682
--- /dev/null
+++ b/lldb/test/API/commands/expression/expr-with-fork/main.cpp
@@ -0,0 +1,21 @@
+#include <sys/wait.h>
+#include <unistd.h>
+
+int fork_and_return(int value, bool use_vfork) {
+  pid_t pid = use_vfork ? vfork() : fork();
+  if (pid == -1)
+    return -1;
+  if (pid == 0) {
+    // child
+    _exit(value);
+  }
+  // parent
+  int status;
+  waitpid(pid, &status, 0);
+  return WEXITSTATUS(status);
+}
+
+int main() {
+  int x = 42;
+  return 0; // break here
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/184815