From 8bb81313a0055125de19cf40e9e76db296a937d7 Mon Sep 17 00:00:00 2001
From: Ariel Abreu <facekapow@outlook.com>
Date: Thu, 24 Mar 2022 13:47:32 -0400
Subject: [PATCH] Add a `set_tracer` call (and implement `get_tracer`)

---
 internal-include/darlingserver/process.hpp |  4 ++
 scripts/generate-rpc-wrappers.py           |  7 ++-
 src/call.cpp                               | 59 +++++++++++++++++++++-
 src/process.cpp                            | 14 +++++
 4 files changed, 81 insertions(+), 3 deletions(-)

diff --git a/internal-include/darlingserver/process.hpp b/internal-include/darlingserver/process.hpp
index ea00a58..1377421 100644
--- a/internal-include/darlingserver/process.hpp
+++ b/internal-include/darlingserver/process.hpp
@@ -79,6 +79,7 @@ namespace DarlingServer {
 		std::unordered_map<uintptr_t, std::weak_ptr<Kqchan::Process>> _listeningKqchannels;
 		dtape_semaphore_t* _dtapeForkWaitSemaphore;
 		Architecture _architecture;
+		std::weak_ptr<Process> _tracerProcess;
 
 #if DSERVER_EXTENDED_DEBUG
 		std::unordered_map<uint32_t, uintptr_t> _registeredNames;
@@ -156,6 +157,9 @@ namespace DarlingServer {
 		MemoryInfo memoryInfo() const;
 		void memoryRegionInfo(uintptr_t address, uintptr_t& startAddress, uint64_t& pageCount, int& protection, uint64_t& mapOffset, bool& shared) const;
 
+		std::shared_ptr<Process> tracerProcess() const;
+		bool setTracerProcess(std::shared_ptr<Process> tracerProcess);
+
 		static std::shared_ptr<Process> currentProcess();
 		static std::shared_ptr<Process> kernelProcess();
 
diff --git a/scripts/generate-rpc-wrappers.py b/scripts/generate-rpc-wrappers.py
index 0bc0d6c..8887ce0 100755
--- a/scripts/generate-rpc-wrappers.py
+++ b/scripts/generate-rpc-wrappers.py
@@ -131,7 +131,7 @@ calls = [
 	]),
 
 	('get_tracer', [], [
-		('tracer', 'uint32_t'),
+		('tracer', 'int32_t'),
 	]),
 
 	('uidgid', [
@@ -188,6 +188,11 @@ calls = [
 		('console', '@fd'),
 	]),
 
+	('set_tracer', [
+		('target', 'int32_t'),
+		('tracer', 'int32_t'),
+	], []),
+
 	#
 	# kqueue channels
 	#
diff --git a/src/call.cpp b/src/call.cpp
index 40fa939..e2bb9a2 100644
--- a/src/call.cpp
+++ b/src/call.cpp
@@ -417,9 +417,21 @@ void DarlingServer::Call::StartedSuspended::processCall() {
 
 void DarlingServer::Call::GetTracer::processCall() {
 	int code = 0;
-	uint32_t tracer = 0;
+	int32_t tracer = 0;
 
-	callLog.warning() << "GetTracer: TODO" << callLog.endLog;
+	if (auto thread = _thread.lock()) {
+		if (auto process = thread->process()) {
+			if (auto tracerProcess = process->tracerProcess()) {
+				tracer = tracerProcess->nsid();
+			} else {
+				// leave `tracer` as 0
+			}
+		} else {
+			code = -ESRCH;
+		}
+	} else {
+		code = -ESRCH;
+	}
 
 	_sendReply(code, tracer);
 };
@@ -769,4 +781,47 @@ void DarlingServer::Call::ConsoleOpen::processCall() {
 	_sendReply(code, sockets[1]);
 };
 
+void DarlingServer::Call::SetTracer::processCall() {
+	int code = 0;
+	std::shared_ptr<Process> targetProcess = nullptr;
+	std::shared_ptr<Process> tracerProcess = nullptr;
+
+	if (_body.target == 0) {
+		if (auto thread = _thread.lock()) {
+			targetProcess = thread->process();
+		}
+	} else {
+		if (auto maybeTargetProcess = processRegistry().lookupEntryByNSID(_body.target)) {
+			targetProcess = *maybeTargetProcess;
+		}
+	}
+
+	if (targetProcess) {
+		if (_body.tracer == 0) {
+			// leave tracer process as nullptr
+		} else {
+			if (auto maybeTracerProcess = processRegistry().lookupEntryByNSID(_body.tracer)) {
+				tracerProcess = *maybeTracerProcess;
+			} else {
+				// intentionally not negated because this is not an internal error;
+				// this is a perfectly valid case
+				code = ESRCH;
+			}
+		}
+
+		if (code == 0) {
+			if (!targetProcess->setTracerProcess(tracerProcess)) {
+				// again, not negated because this isn't an internal error;
+				// simply indicates there was already a tracer set for the target
+				code = EPERM;
+			}
+		}
+	} else {
+		// ditto from before
+		code = ESRCH;
+	}
+
+	_sendReply(code);
+};
+
 DSERVER_CLASS_SOURCE_DEFS;
diff --git a/src/process.cpp b/src/process.cpp
index f94c79e..a86ee62 100644
--- a/src/process.cpp
+++ b/src/process.cpp
@@ -530,3 +530,17 @@ void DarlingServer::Process::_clearPortSet(dtape_port_set_id_t portSetID) {
 };
 
 #endif
+
+std::shared_ptr<DarlingServer::Process> DarlingServer::Process::tracerProcess() const {
+	std::shared_lock lock(_rwlock);
+	return _tracerProcess.lock();
+};
+
+bool DarlingServer::Process::setTracerProcess(std::shared_ptr<Process> tracerProcess) {
+	std::unique_lock lock(_rwlock);
+	if (!_tracerProcess.expired()) {
+		return false;
+	}
+	_tracerProcess = tracerProcess;
+	return true;
+};