[trace][intelpt] Support system-wide tracing [4] - Support per core tracing on lldb-server

This diffs implements per-core tracing on lldb-server. It also includes tests that ensure that tracing can be initiated from the client and that the jLLDBGetState ppacket returns the list of trace buffers per core.

This doesn't include any decoder changes.

Finally, this makes some little changes here and there improving the existing code.

A specific piece of code that can't reliably be tested is when tracing
per core fails due to permissions. In this case we add a
troubleshooting message and this is the manual test:

```
/proc/sys/kernel/perf_event_paranoid set to 1

(lldb) process trace start --per-core-tracing                                         error: perf event syscall failed: Permission denied
 You might need that /proc/sys/kernel/perf_event_paranoid has a value of 0 or -1.
``

Differential Revision: https://reviews.llvm.org/D124858

1 files changed, 2 insertions, 5 deletions

diff --git a/lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp b/lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp
index 78d1b3a..37da1f1 100644
--- a/lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp
+++ b/lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp
@@ -312,7 +312,7 @@ NativeProcessLinux::NativeProcessLinux(::pid_t pid, int terminal_fd,
                                        const ArchSpec &arch, MainLoop &mainloop,
                                        llvm::ArrayRef<::pid_t> tids)
     : NativeProcessELF(pid, terminal_fd, delegate), m_arch(arch),
-      m_main_loop(mainloop) {
+      m_main_loop(mainloop), m_intel_pt_collector(*this) {
   if (m_terminal_fd != -1) {
     Status status = EnsureFDFlags(m_terminal_fd, O_NONBLOCK);
     assert(status.Success());
@@ -1967,10 +1967,7 @@ Error NativeProcessLinux::TraceStart(StringRef json_request, StringRef type) {
     if (Expected<TraceIntelPTStartRequest> request =
             json::parse<TraceIntelPTStartRequest>(json_request,
                                                   "TraceIntelPTStartRequest")) {
-      std::vector<lldb::tid_t> process_threads;
-      for (auto &thread : m_threads)
-        process_threads.push_back(thread->GetID());
-      return m_intel_pt_collector.TraceStart(*request, process_threads);
+      return m_intel_pt_collector.TraceStart(*request);
     } else
       return request.takeError();
   }