[Lldb-commits] [lldb] [lldb-mcp] Launch lldb on demand, if needed. (PR #158701)
John Harrison via lldb-commits
lldb-commits at lists.llvm.org
Tue Sep 16 09:33:29 PDT 2025
https://github.com/ashgti updated https://github.com/llvm/llvm-project/pull/158701
>From 39b27ffc60fe30e88e42918f2c3382369f06f3df Mon Sep 17 00:00:00 2001
From: John Harrison <harjohn at google.com>
Date: Mon, 15 Sep 2025 10:30:04 -0700
Subject: [PATCH 1/5] [lldb-mcp] Launch lldb on demand, if needed.
Adding support for launching lldb with `-O protocol start MCP` if a valid ~/.lldb/lldb-mcp-*.json` file is not found.
---
lldb/source/Host/common/Socket.cpp | 2 +-
lldb/tools/lldb-mcp/lldb-mcp.cpp | 122 +++++++++++++++++++++--------
2 files changed, 92 insertions(+), 32 deletions(-)
diff --git a/lldb/source/Host/common/Socket.cpp b/lldb/source/Host/common/Socket.cpp
index 3511cde8bb36f..bc3d849c5c6c6 100644
--- a/lldb/source/Host/common/Socket.cpp
+++ b/lldb/source/Host/common/Socket.cpp
@@ -506,7 +506,7 @@ Socket::GetProtocolAndMode(llvm::StringRef scheme) {
.Case("unix-abstract-accept",
ProtocolModePair{SocketProtocol::ProtocolUnixAbstract,
SocketMode::ModeAccept})
- .Cases("connect", "tcp-connect",
+ .Cases("connect", "tcp-connect", "connection",
ProtocolModePair{SocketProtocol::ProtocolTcp,
SocketMode::ModeConnect})
.Case("udp", ProtocolModePair{SocketProtocol::ProtocolTcp,
diff --git a/lldb/tools/lldb-mcp/lldb-mcp.cpp b/lldb/tools/lldb-mcp/lldb-mcp.cpp
index 12545dcf3a3cc..42e82709dd9df 100644
--- a/lldb/tools/lldb-mcp/lldb-mcp.cpp
+++ b/lldb/tools/lldb-mcp/lldb-mcp.cpp
@@ -8,12 +8,16 @@
#include "lldb/Host/Config.h"
#include "lldb/Host/File.h"
+#include "lldb/Host/FileSystem.h"
+#include "lldb/Host/Host.h"
#include "lldb/Host/MainLoop.h"
#include "lldb/Host/MainLoopBase.h"
+#include "lldb/Host/ProcessLaunchInfo.h"
#include "lldb/Host/Socket.h"
#include "lldb/Initialization/SystemInitializerCommon.h"
#include "lldb/Initialization/SystemLifetimeManager.h"
#include "lldb/Protocol/MCP/Server.h"
+#include "lldb/Utility/FileSpec.h"
#include "lldb/Utility/Status.h"
#include "lldb/Utility/UriParser.h"
#include "lldb/lldb-forward.h"
@@ -24,7 +28,9 @@
#include "llvm/Support/ManagedStatic.h"
#include "llvm/Support/Signals.h"
#include "llvm/Support/WithColor.h"
+#include <chrono>
#include <cstdlib>
+#include <future>
#include <memory>
#if defined(_WIN32)
@@ -35,13 +41,19 @@ using namespace llvm;
using namespace lldb;
using namespace lldb_protocol::mcp;
+using lldb_private::Environment;
using lldb_private::File;
+using lldb_private::FileSpec;
+using lldb_private::FileSystem;
+using lldb_private::Host;
using lldb_private::MainLoop;
using lldb_private::MainLoopBase;
using lldb_private::NativeFile;
namespace {
+constexpr size_t kForwardIOBufferSize = 1024;
+
inline void exitWithError(llvm::Error Err, StringRef Prefix = "") {
handleAllErrors(std::move(Err), [&](ErrorInfoBase &Info) {
WithColor::error(errs(), Prefix) << Info.message() << '\n';
@@ -49,10 +61,68 @@ inline void exitWithError(llvm::Error Err, StringRef Prefix = "") {
std::exit(EXIT_FAILURE);
}
-constexpr size_t kForwardIOBufferSize = 1024;
+FileSpec driverPath() {
+ Environment host_env = Host::GetEnvironment();
+
+ // Check if an override for which lldb we're using exists, otherwise look next
+ // to the current binary.
+ std::string lldb_exe_path = host_env.lookup("LLDB_EXE_PATH");
+ auto &fs = FileSystem::Instance();
+ if (fs.Exists(lldb_exe_path)) {
+ return FileSpec(lldb_exe_path);
+ }
+ FileSpec lldb_exec_spec = lldb_private::HostInfo::GetProgramFileSpec();
+ lldb_exec_spec.SetFilename("lldb");
+ return lldb_exec_spec;
+}
+
+llvm::Error launch() {
+ FileSpec lldb_exec = driverPath();
+ lldb_private::ProcessLaunchInfo info;
+ info.SetExecutableFile(lldb_exec,
+ /*add_exe_file_as_first_arg=*/true);
+ info.GetArguments().AppendArgument("-O");
+ info.GetArguments().AppendArgument("protocol start MCP");
+ std::promise<int> exit_status;
+ info.SetMonitorProcessCallback([&](lldb::pid_t pid, int signal, int status) {
+ exit_status.set_value(status);
+ });
+
+ return Host::LaunchProcess(info).takeError();
+}
+
+Expected<ServerInfo> loadOrStart(
+ lldb_private::Timeout<std::micro> timeout = std::chrono::seconds(30)) {
+ using namespace std::chrono;
+ bool started = false;
+
+ auto deadline = steady_clock::now() + *timeout;
+ while (steady_clock::now() < deadline) {
+ auto servers = ServerInfo::Load();
+ if (!servers)
+ return servers.takeError();
+
+ if (servers->empty()) {
+ if (!started) {
+ started = true;
+ if (llvm::Error err = launch())
+ return std::move(err);
+ }
+ std::this_thread::sleep_for(std::chrono::microseconds(250));
+ continue;
+ }
+
+ if (servers->size() > 1)
+ return createStringError("To many MCP servers running, picking a "
+ "specific one is not yet implemented");
+
+ return servers->front();
+ }
+
+ return createStringError("timed out waiting for MCP server to start");
+}
-void forwardIO(lldb_private::MainLoopBase &loop, lldb::IOObjectSP &from,
- lldb::IOObjectSP &to) {
+void forwardIO(MainLoopBase &loop, IOObjectSP &from, IOObjectSP &to) {
char buf[kForwardIOBufferSize];
size_t num_bytes = sizeof(buf);
@@ -67,21 +137,24 @@ void forwardIO(lldb_private::MainLoopBase &loop, lldb::IOObjectSP &from,
exitWithError(std::move(err));
}
-void connectAndForwardIO(lldb_private::MainLoop &loop, ServerInfo &info,
- IOObjectSP &input_sp, IOObjectSP &output_sp) {
+llvm::Error connectAndForwardIO(lldb_private::MainLoop &loop, ServerInfo &info,
+ IOObjectSP &input_sp, IOObjectSP &output_sp) {
auto uri = lldb_private::URI::Parse(info.connection_uri);
if (!uri)
- exitWithError(createStringError("invalid connection_uri"));
+ return createStringError("invalid connection_uri");
std::optional<lldb_private::Socket::ProtocolModePair> protocol_and_mode =
lldb_private::Socket::GetProtocolAndMode(uri->scheme);
+ if (!protocol_and_mode)
+ return createStringError("unknown protocol scheme");
+
lldb_private::Status status;
std::unique_ptr<lldb_private::Socket> sock =
lldb_private::Socket::Create(protocol_and_mode->first, status);
if (status.Fail())
- exitWithError(status.takeError());
+ return status.takeError();
if (uri->port && !uri->hostname.empty())
status = sock->Connect(
@@ -89,24 +162,22 @@ void connectAndForwardIO(lldb_private::MainLoop &loop, ServerInfo &info,
else
status = sock->Connect(uri->path);
if (status.Fail())
- exitWithError(status.takeError());
+ return status.takeError();
IOObjectSP sock_sp = std::move(sock);
auto input_handle = loop.RegisterReadObject(
input_sp, std::bind(forwardIO, std::placeholders::_1, input_sp, sock_sp),
status);
if (status.Fail())
- exitWithError(status.takeError());
+ return status.takeError();
auto socket_handle = loop.RegisterReadObject(
sock_sp, std::bind(forwardIO, std::placeholders::_1, sock_sp, output_sp),
status);
if (status.Fail())
- exitWithError(status.takeError());
+ return status.takeError();
- status = loop.Run();
- if (status.Fail())
- exitWithError(status.takeError());
+ return loop.Run().takeError();
}
llvm::ManagedStatic<lldb_private::SystemLifetimeManager> g_debugger_lifetime;
@@ -147,30 +218,19 @@ int main(int argc, char *argv[]) {
IOObjectSP output_sp = std::make_shared<NativeFile>(
fileno(stdout), File::eOpenOptionWriteOnly, NativeFile::Unowned);
- static MainLoop loop;
+ Expected<ServerInfo> server_info = loadOrStart();
+ if (!server_info)
+ exitWithError(server_info.takeError());
+ static MainLoop loop;
sys::SetInterruptFunction([]() {
loop.AddPendingCallback(
[](MainLoopBase &loop) { loop.RequestTermination(); });
});
- auto existing_servers = ServerInfo::Load();
-
- if (!existing_servers)
- exitWithError(existing_servers.takeError());
-
- // FIXME: Launch `lldb -o 'protocol start MCP'`.
- if (existing_servers->empty())
- exitWithError(createStringError("No MCP servers running"));
-
- // FIXME: Support selecting a specific server.
- if (existing_servers->size() != 1)
- exitWithError(
- createStringError("To many MCP servers running, picking a specific "
- "one is not yet implemented."));
-
- ServerInfo &info = existing_servers->front();
- connectAndForwardIO(loop, info, input_sp, output_sp);
+ if (llvm::Error error =
+ connectAndForwardIO(loop, *server_info, input_sp, output_sp))
+ exitWithError(std::move(error));
return EXIT_SUCCESS;
}
>From b0c9485ccb04896b7fe8d89506c220692fa8f29b Mon Sep 17 00:00:00 2001
From: John Harrison <harjohn at google.com>
Date: Mon, 15 Sep 2025 11:02:43 -0700
Subject: [PATCH 2/5] Adding some comments and removing some dead code.
---
lldb/tools/lldb-mcp/lldb-mcp.cpp | 18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)
diff --git a/lldb/tools/lldb-mcp/lldb-mcp.cpp b/lldb/tools/lldb-mcp/lldb-mcp.cpp
index 42e82709dd9df..6c306ad40e306 100644
--- a/lldb/tools/lldb-mcp/lldb-mcp.cpp
+++ b/lldb/tools/lldb-mcp/lldb-mcp.cpp
@@ -30,8 +30,8 @@
#include "llvm/Support/WithColor.h"
#include <chrono>
#include <cstdlib>
-#include <future>
#include <memory>
+#include <thread>
#if defined(_WIN32)
#include <fcntl.h>
@@ -71,6 +71,7 @@ FileSpec driverPath() {
if (fs.Exists(lldb_exe_path)) {
return FileSpec(lldb_exe_path);
}
+
FileSpec lldb_exec_spec = lldb_private::HostInfo::GetProgramFileSpec();
lldb_exec_spec.SetFilename("lldb");
return lldb_exec_spec;
@@ -83,22 +84,18 @@ llvm::Error launch() {
/*add_exe_file_as_first_arg=*/true);
info.GetArguments().AppendArgument("-O");
info.GetArguments().AppendArgument("protocol start MCP");
- std::promise<int> exit_status;
- info.SetMonitorProcessCallback([&](lldb::pid_t pid, int signal, int status) {
- exit_status.set_value(status);
- });
-
return Host::LaunchProcess(info).takeError();
}
Expected<ServerInfo> loadOrStart(
+ // FIXME: This should become a CLI arg.
lldb_private::Timeout<std::micro> timeout = std::chrono::seconds(30)) {
using namespace std::chrono;
bool started = false;
- auto deadline = steady_clock::now() + *timeout;
+ const auto deadline = steady_clock::now() + *timeout;
while (steady_clock::now() < deadline) {
- auto servers = ServerInfo::Load();
+ Expected<std::vector<ServerInfo>> servers = ServerInfo::Load();
if (!servers)
return servers.takeError();
@@ -108,10 +105,13 @@ Expected<ServerInfo> loadOrStart(
if (llvm::Error err = launch())
return std::move(err);
}
- std::this_thread::sleep_for(std::chrono::microseconds(250));
+
+ // FIXME: Can we use MainLoop to watch the directory?
+ std::this_thread::sleep_for(microseconds(250));
continue;
}
+ // FIXME: Support selecting / multiplexing a specific lldb instance.
if (servers->size() > 1)
return createStringError("To many MCP servers running, picking a "
"specific one is not yet implemented");
>From 2c4f00353c81edbecce5058a7e9510b8742b2932 Mon Sep 17 00:00:00 2001
From: John Harrison <ash at greaterthaninfinity.com>
Date: Tue, 16 Sep 2025 09:00:13 -0700
Subject: [PATCH 3/5] Update lldb/tools/lldb-mcp/lldb-mcp.cpp
Co-authored-by: Jonas Devlieghere <jonas at devlieghere.com>
---
lldb/tools/lldb-mcp/lldb-mcp.cpp | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/lldb/tools/lldb-mcp/lldb-mcp.cpp b/lldb/tools/lldb-mcp/lldb-mcp.cpp
index 6c306ad40e306..775e86b8067eb 100644
--- a/lldb/tools/lldb-mcp/lldb-mcp.cpp
+++ b/lldb/tools/lldb-mcp/lldb-mcp.cpp
@@ -113,7 +113,7 @@ Expected<ServerInfo> loadOrStart(
// FIXME: Support selecting / multiplexing a specific lldb instance.
if (servers->size() > 1)
- return createStringError("To many MCP servers running, picking a "
+ return createStringError("too many MCP servers running, picking a "
"specific one is not yet implemented");
return servers->front();
>From 089c985de9ff62c23f31baa143f238bf645291ec Mon Sep 17 00:00:00 2001
From: John Harrison <ash at greaterthaninfinity.com>
Date: Tue, 16 Sep 2025 09:00:23 -0700
Subject: [PATCH 4/5] Update lldb/tools/lldb-mcp/lldb-mcp.cpp
Co-authored-by: Jonas Devlieghere <jonas at devlieghere.com>
---
lldb/tools/lldb-mcp/lldb-mcp.cpp | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/lldb/tools/lldb-mcp/lldb-mcp.cpp b/lldb/tools/lldb-mcp/lldb-mcp.cpp
index 775e86b8067eb..af8424d2b39a1 100644
--- a/lldb/tools/lldb-mcp/lldb-mcp.cpp
+++ b/lldb/tools/lldb-mcp/lldb-mcp.cpp
@@ -68,9 +68,8 @@ FileSpec driverPath() {
// to the current binary.
std::string lldb_exe_path = host_env.lookup("LLDB_EXE_PATH");
auto &fs = FileSystem::Instance();
- if (fs.Exists(lldb_exe_path)) {
+ if (fs.Exists(lldb_exe_path))
return FileSpec(lldb_exe_path);
- }
FileSpec lldb_exec_spec = lldb_private::HostInfo::GetProgramFileSpec();
lldb_exec_spec.SetFilename("lldb");
>From 37597b4472096e08ab896e5afd842b4f6c27efd2 Mon Sep 17 00:00:00 2001
From: John Harrison <harjohn at google.com>
Date: Tue, 16 Sep 2025 09:33:12 -0700
Subject: [PATCH 5/5] Adding in the Windows name of the driver executable.
---
lldb/tools/lldb-mcp/lldb-mcp.cpp | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/lldb/tools/lldb-mcp/lldb-mcp.cpp b/lldb/tools/lldb-mcp/lldb-mcp.cpp
index af8424d2b39a1..68e987237cc69 100644
--- a/lldb/tools/lldb-mcp/lldb-mcp.cpp
+++ b/lldb/tools/lldb-mcp/lldb-mcp.cpp
@@ -52,6 +52,12 @@ using lldb_private::NativeFile;
namespace {
+#if defined(_WIN32)
+constexpr StringLiteral kDriverName = "lldb.exe";
+#else
+constexpr StringLiteral kDriverName = "lldb";
+#endif
+
constexpr size_t kForwardIOBufferSize = 1024;
inline void exitWithError(llvm::Error Err, StringRef Prefix = "") {
@@ -68,11 +74,11 @@ FileSpec driverPath() {
// to the current binary.
std::string lldb_exe_path = host_env.lookup("LLDB_EXE_PATH");
auto &fs = FileSystem::Instance();
- if (fs.Exists(lldb_exe_path))
+ if (fs.Exists(lldb_exe_path))
return FileSpec(lldb_exe_path);
FileSpec lldb_exec_spec = lldb_private::HostInfo::GetProgramFileSpec();
- lldb_exec_spec.SetFilename("lldb");
+ lldb_exec_spec.SetFilename(kDriverName);
return lldb_exec_spec;
}
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