[lldb] [gdb-remote client] Remove breakpoints throughout vfork

Temporarily remove breakpoints for the duration of vfork, in order
to prevent them from triggering in the child process.  Restore them
once the server reports that vfork has finished and it is ready to
resume execution.

Differential Revision: https://reviews.llvm.org/D100267

Author: mgorny

lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp

@@ -265,7 +265,8 @@ ProcessGDBRemote::ProcessGDBRemote(lldb::TargetSP target_sp,
       m_waiting_for_attach(false), m_destroy_tried_resuming(false),
       m_command_sp(), m_breakpoint_pc_offset(0),
       m_initial_tid(LLDB_INVALID_THREAD_ID), m_replay_mode(false),
-      m_allow_flash_writes(false), m_erased_flash_ranges() {
+      m_allow_flash_writes(false), m_erased_flash_ranges(),
+      m_vfork_in_progress(false) {
   m_async_broadcaster.SetEventName(eBroadcastBitAsyncThreadShouldExit,
                                    "async thread should exit");
   m_async_broadcaster.SetEventName(eBroadcastBitAsyncContinue,
@@ -5534,6 +5535,13 @@ void ProcessGDBRemote::DidFork(lldb::pid_t child_pid, lldb::tid_t child_tid) {
 void ProcessGDBRemote::DidVFork(lldb::pid_t child_pid, lldb::tid_t child_tid) {
   Log *log(ProcessGDBRemoteLog::GetLogIfAllCategoriesSet(GDBR_LOG_PROCESS));
 
+  assert(!m_vfork_in_progress);
+  m_vfork_in_progress = true;
+
+  // Disable all software breakpoints for the duration of vfork.
+  if (m_gdb_comm.SupportsGDBStoppointPacket(eBreakpointSoftware))
+    DidForkSwitchSoftwareBreakpoints(false);
+
   LLDB_LOG(log, "Detaching forked child {0}", child_pid);
   Status error = m_gdb_comm.Detach(false, child_pid);
   if (error.Fail()) {
@@ -5543,3 +5551,12 @@ void ProcessGDBRemote::DidVFork(lldb::pid_t child_pid, lldb::tid_t child_tid) {
       return;
   }
 }
+
+void ProcessGDBRemote::DidVForkDone() {
+  assert(m_vfork_in_progress);
+  m_vfork_in_progress = false;
+
+  // Reenable all software breakpoints that were enabled before vfork.
+  if (m_gdb_comm.SupportsGDBStoppointPacket(eBreakpointSoftware))
+    DidForkSwitchSoftwareBreakpoints(true);
+}

lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.h

@@ -232,6 +232,7 @@ class ProcessGDBRemote : public Process,
 
   void DidFork(lldb::pid_t child_pid, lldb::tid_t child_tid) override;
   void DidVFork(lldb::pid_t child_pid, lldb::tid_t child_tid) override;
+  void DidVForkDone() override;
 
 protected:
   friend class ThreadGDBRemote;
@@ -296,6 +297,8 @@ class ProcessGDBRemote : public Process,
   using FlashRange = FlashRangeVector::Entry;
   FlashRangeVector m_erased_flash_ranges;
 
+  bool m_vfork_in_progress;
+
   // Accessors
   bool IsRunning(lldb::StateType state) {
     return state == lldb::eStateRunning || IsStepping(state);

lldb/test/Shell/Subprocess/vfork-follow-parent-softbp.test

@@ -0,0 +1,13 @@
+# REQUIRES: native
+# UNSUPPORTED: system-darwin
+# UNSUPPORTED: system-windows
+# RUN: %clangxx_host %p/Inputs/fork.cpp -DTEST_FORK=vfork -o %t
+# RUN: %lldb -b -s %s %t | FileCheck %s
+b parent_func
+b child_func
+process launch
+# CHECK-NOT: function run in parent
+# CHECK: stop reason = breakpoint
+continue
+# CHECK: function run in parent
+# CHECK: child exited: 0