[lldb] Have lldb-server assign ports to children in platform mode #88845
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@llvm/pr-subscribers-lldb Author: Anthony Ha (Awfa) Changes
How the platform code seems to work is that it listens on a port, and whenever there's an incoming connection, it forks the process to handle the connection. To handle the port flags, the main process uses an instance of the helper class However, in the current code, this works only once. After the first connection is handled by forking a child process, the main platform listener code loops around, and then 'forgets' about the port map. This is because this code: GDBRemoteCommunicationServerPlatform platform(
acceptor_up->GetSocketProtocol(), acceptor_up->GetSocketScheme());
if (!gdbserver_portmap.empty()) {
platform.SetPortMap(std::move(gdbserver_portmap));
}is within the connection listening loop. This results in the This PR fixes this issue by having the port map be maintained by the parent platform listener process. On connection, the listener allocates a single available port from the port map, associates the child process pid with the port, and lets the connection handling child use that single port number. Additionally, when cleaning up child processes, the main listener process tracks the child that exited to deallocate the previously associated port, so it can be reused for a new connection. For review:
Full diff: https://github.com/llvm/llvm-project/pull/88845.diff 1 Files Affected:
diff --git a/lldb/tools/lldb-server/lldb-platform.cpp b/lldb/tools/lldb-server/lldb-platform.cpp
index 3e126584eb25b4..384709ba79b656 100644
--- a/lldb/tools/lldb-server/lldb-platform.cpp
+++ b/lldb/tools/lldb-server/lldb-platform.cpp
@@ -282,17 +282,10 @@ int main_platform(int argc, char *argv[]) {
}
}
- do {
- GDBRemoteCommunicationServerPlatform platform(
- acceptor_up->GetSocketProtocol(), acceptor_up->GetSocketScheme());
-
- if (port_offset > 0)
- platform.SetPortOffset(port_offset);
-
- if (!gdbserver_portmap.empty()) {
- platform.SetPortMap(std::move(gdbserver_portmap));
- }
+ GDBRemoteCommunicationServerPlatform platform(
+ acceptor_up->GetSocketProtocol(), acceptor_up->GetSocketScheme());
+ do {
const bool children_inherit_accept_socket = true;
Connection *conn = nullptr;
error = acceptor_up->Accept(children_inherit_accept_socket, conn);
@@ -301,13 +294,31 @@ int main_platform(int argc, char *argv[]) {
exit(socket_error);
}
printf("Connection established.\n");
+
+ std::optional<uint16_t> port = 0;
if (g_server) {
// Collect child zombie processes.
#if !defined(_WIN32)
- while (waitpid(-1, nullptr, WNOHANG) > 0)
- ;
+ auto waitResult = waitpid(-1, nullptr, WNOHANG);
+ while (waitResult > 0) {
+ // waitResult is the child pid
+ gdbserver_portmap.FreePortForProcess(waitResult);
+ waitResult = waitpid(-1, nullptr, WNOHANG);
+ }
#endif
- if (fork()) {
+ llvm::Expected<uint16_t> available_port =
+ gdbserver_portmap.GetNextAvailablePort();
+ if (available_port)
+ port = *available_port;
+
+ else {
+ fprintf(stderr, "no available port for connection - dropping...\n");
+ delete conn;
+ continue;
+ }
+ auto childPid = fork();
+ if (childPid) {
+ gdbserver_portmap.AssociatePortWithProcess(*available_port, childPid);
// Parent doesn't need a connection to the lldb client
delete conn;
@@ -324,6 +335,10 @@ int main_platform(int argc, char *argv[]) {
// connections while a connection is active.
acceptor_up.reset();
}
+
+ GDBRemoteCommunicationServerPlatform::PortMap portmap_for_child;
+ portmap_for_child.AllowPort(*port);
+ platform.SetPortMap(std::move(portmap_for_child));
platform.SetConnection(std::unique_ptr<Connection>(conn));
if (platform.IsConnected()) {
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I think this will fix #47549. And make the note at the end of For testing we might be able to send the platform the gdbserver spawn packets and check that it doesn't return the same port each time. There are tests in Given the only existing tests are for the command line validation, I'd be ok not adding tests for this. |
[lldb] Have lldb-server assign ports to children in platform mode
[lldb] Have lldb-server assign ports to children in platform mode
Removing this is the last thing to do here. |
[lldb] Have lldb-server assign ports to children in platform mode
Fixed! If this looks good to you, would you also be able to merge it? I don't have write permissions. |
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Is there a way to invoke BuildBot on this branch before it's merged in by the way? I got bit on another PR where it caught some failures I wished were caught before merge. |
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Nope, that would be lovely and is closer than ever with the move to GitHub, but not here yet. |
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@Awfa Congratulations on having your first Pull Request (PR) merged into the LLVM Project! Your changes will be combined with recent changes from other authors, then tested Please check whether problems have been caused by your change specifically, as How to do this, and the rest of the post-merge process, is covered in detail here. If your change does cause a problem, it may be reverted, or you can revert it yourself. If you don't get any reports, no action is required from you. Your changes are working as expected, well done! |
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Hi @Awfa, we start getting failures for some LLDB API tests after these changes. The tests are running on Jetson AGX/Cortex a78 (aarch64) board with Ubuntu Linux 22.04 on it. The failed tests get failed with the following error message: We run these tests in 8 threads. The The build host is Windows, the remote target host is Ubuntu Linux. Affected tests:
Reverting of these changes fixes the problem. Thanks. |
Fixes #47549
lldb-server's platform mode seems to have an issue with its--min-gdbserver-port--max-gdbserver-portflags (and probably the--gdbserver-portflag, but I didn't test it).How the platform code seems to work is that it listens on a port, and whenever there's an incoming connection, it forks the process to handle the connection. To handle the port flags, the main process uses an instance of the helper class
GDBRemoteCommunicationServerPlatform::PortMap, that can be configured and track usages of ports. The child process handling the platform connection, can then use the port map to allocate a port for the gdb-server connection it will make (this is another process it spawns).However, in the current code, this works only once. After the first connection is handled by forking a child process, the main platform listener code loops around, and then 'forgets' about the port map. This is because this code:
is within the connection listening loop. This results in the
gdbserver_portmapbeing moved into the platform object at the beginning of the first iteration of the loop, but on the second iteration, after the first fork, the next instance of the platform object will not have its platform port mapped.The result of this bug is that subsequent connections to the platform, when spawning the gdb-remote connection, will be supplied a random port - which isn't bounded by the
--min-gdbserver-portand--max-gdbserver--portparameters passed in by the user.This PR fixes this issue by having the port map be maintained by the parent platform listener process. On connection, the listener allocates a single available port from the port map, associates the child process pid with the port, and lets the connection handling child use that single port number.
Additionally, when cleaning up child processes, the main listener process tracks the child that exited to deallocate the previously associated port, so it can be reused for a new connection.