[Lldb-commits] [lldb] [lldb] fix software breakpoint removing in multithreaded process while stepping (PR #127506)

[via lldb-commits]

https://github.com/dlav-sc created https://github.com/llvm/llvm-project/pull/127506

I have encountered with the issue that sometimes lldb-server can't remove internal software breakpoints in a multithread process and as a result the process freezes.

The source of the issue was that lldb-server tried to read/write memory of the process using a tid of the exited thread and received 'No such process' error from ptrace.

This patch sets an existing thread as the current one for this process before software breakpoints removing.

>From 8beff49a1b0af7b5f2298a73b9bb1a17670f673b Mon Sep 17 00:00:00 2001
From: Daniil Avdeev <daniil.avdeev at syntacore.com>
Date: Wed, 12 Feb 2025 13:15:53 +0000
Subject: [PATCH] [lldb] fix software breakpoint removing in multithreaded
 process while stepping

I have encountered with the issue that sometimes lldb-server can't remove
internal software breakpoints in a multithread process and as a result
the process freezes.

The source of the issue was that lldb-server tried to read/write memory
of the process using a tid of the exited thread and received 'No such
process' error from ptrace.

This patch sets an existing thread as the current one for this process
before software breakpoints removing.
---
 lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp b/lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp
index 7f2aba0e4eb2c..fe16ec73c0404 100644
--- a/lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp
+++ b/lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp
@@ -1959,6 +1959,7 @@ void NativeProcessLinux::SignalIfAllThreadsStopped() {
 
   // Clear any temporary breakpoints we used to implement software single
   // stepping.
+  SetCurrentThreadID(m_pending_notification_tid);
   for (const auto &thread_info : m_threads_stepping_with_breakpoint) {
     Status error = RemoveBreakpoint(thread_info.second);
     if (error.Fail())
@@ -1968,7 +1969,6 @@ void NativeProcessLinux::SignalIfAllThreadsStopped() {
   m_threads_stepping_with_breakpoint.clear();
 
   // Notify the delegate about the stop
-  SetCurrentThreadID(m_pending_notification_tid);
   SetState(StateType::eStateStopped, true);
   m_pending_notification_tid = LLDB_INVALID_THREAD_ID;
 }