Kernel: Add syscall performance event type

This allows tracing the syscalls made by a thread through the kernel's
performance event framework, which is similar in principle to strace.

Currently, this merely logs a stack backtrace to the current thread's
performance event buffer whenever a syscall is made, if profiling is
enabled. Future improvements could include tracing the arguments and
the return value, for example.

Kernel/PerformanceEventBuffer.cpp

@@ -135,6 +135,8 @@ KResult PerformanceEventBuffer::append_with_ip_and_bp(ProcessID pid, ThreadID ti
         break;
     case PERF_EVENT_PAGE_FAULT:
         break;
+    case PERF_EVENT_SYSCALL:
+        break;
     default:
         return EINVAL;
     }
@@ -226,6 +228,9 @@ bool PerformanceEventBuffer::to_json_impl(Serializer& object) const
         case PERF_EVENT_PAGE_FAULT:
             event_object.add("type", "page_fault");
             break;
+        case PERF_EVENT_SYSCALL:
+            event_object.add("type", "syscall");
+            break;
         }
         event_object.add("pid", event.pid);
         event_object.add("tid", event.tid);

Kernel/PerformanceManager.h

@@ -119,6 +119,17 @@ public:
         }
     }
 
+    inline static void add_syscall_event(Thread& thread, const RegisterState& regs)
+    {
+        if (thread.is_profiling_suppressed())
+            return;
+        if (auto* event_buffer = thread.process().current_perf_events_buffer()) {
+            [[maybe_unused]] auto rc = event_buffer->append_with_ip_and_bp(
+                thread.pid(), thread.tid(),
+                regs.ip(), regs.bp(), PERF_EVENT_SYSCALL, 0, 0, 0, nullptr);
+        }
+    }
+
     inline static void timer_tick(RegisterState const& regs)
     {
         static Time last_wakeup;

Kernel/Syscall.cpp

@@ -9,6 +9,7 @@
 #include <Kernel/Arch/x86/TrapFrame.h>
 #include <Kernel/Memory/MemoryManager.h>
 #include <Kernel/Panic.h>
+#include <Kernel/PerformanceManager.h>
 #include <Kernel/Process.h>
 #include <Kernel/Sections.h>
 #include <Kernel/ThreadTracer.h>
@@ -108,6 +109,8 @@ KResultOr<FlatPtr> handle(RegisterState& regs, FlatPtr function, FlatPtr arg1, F
     auto& process = current_thread->process();
     current_thread->did_syscall();
 
+    PerformanceManager::add_syscall_event(*current_thread, regs);
+
     if (function >= Function::__Count) {
         dbgln("Unknown syscall {} requested ({:p}, {:p}, {:p}, {:p})", function, arg1, arg2, arg3, arg4);
         return ENOSYS;

Kernel/UnixTypes.h

@@ -62,6 +62,7 @@ enum {
     PERF_EVENT_KMALLOC = 2048,
     PERF_EVENT_KFREE = 4096,
     PERF_EVENT_PAGE_FAULT = 8192,
+    PERF_EVENT_SYSCALL = 16384,
 };
 
 #define WNOHANG 1