[lldb] [Process/FreeBSDKernel] Support finding all processes

Include the complete list of threads of all running processes
in the FreeBSDKernel plugin.  This makes it possible to inspect
the states (including partial register dumps from PCB) of all kernel
and userspace threads at the time of crash, or at the time of reading
/dev/mem first.

Differential Revision: https://reviews.llvm.org/D116255

lldb/source/Plugins/Process/FreeBSDKernel/ProcessFreeBSDKernel.cpp

@@ -137,12 +137,115 @@ bool ProcessFreeBSDKernel::DoUpdateThreadList(ThreadList &old_thread_list,
       return false;
     }
 
-    const Symbol *pcb_sym =
-        GetTarget().GetExecutableModule()->FindFirstSymbolWithNameAndType(
-            ConstString("dumppcb"));
-    ThreadSP thread_sp(new ThreadFreeBSDKernel(
-        *this, 1, pcb_sym ? pcb_sym->GetFileAddress() : LLDB_INVALID_ADDRESS));
-    new_thread_list.AddThread(thread_sp);
+    Status error;
+
+    // struct field offsets are written as symbols so that we don't have
+    // to figure them out ourselves
+    int32_t offset_p_list = ReadSignedIntegerFromMemory(
+        FindSymbol("proc_off_p_list"), 4, -1, error);
+    int32_t offset_p_pid =
+        ReadSignedIntegerFromMemory(FindSymbol("proc_off_p_pid"), 4, -1, error);
+    int32_t offset_p_threads = ReadSignedIntegerFromMemory(
+        FindSymbol("proc_off_p_threads"), 4, -1, error);
+    int32_t offset_p_comm = ReadSignedIntegerFromMemory(
+        FindSymbol("proc_off_p_comm"), 4, -1, error);
+
+    int32_t offset_td_tid = ReadSignedIntegerFromMemory(
+        FindSymbol("thread_off_td_tid"), 4, -1, error);
+    int32_t offset_td_plist = ReadSignedIntegerFromMemory(
+        FindSymbol("thread_off_td_plist"), 4, -1, error);
+    int32_t offset_td_pcb = ReadSignedIntegerFromMemory(
+        FindSymbol("thread_off_td_pcb"), 4, -1, error);
+    int32_t offset_td_oncpu = ReadSignedIntegerFromMemory(
+        FindSymbol("thread_off_td_oncpu"), 4, -1, error);
+    int32_t offset_td_name = ReadSignedIntegerFromMemory(
+        FindSymbol("thread_off_td_name"), 4, -1, error);
+
+    // fail if we were not able to read any of the offsets
+    if (offset_p_list == -1 || offset_p_pid == -1 || offset_p_threads == -1 ||
+        offset_p_comm == -1 || offset_td_tid == -1 || offset_td_plist == -1 ||
+        offset_td_pcb == -1 || offset_td_oncpu == -1 || offset_td_name == -1)
+      return false;
+
+    // dumptid contains the thread-id of the crashing thread
+    // dumppcb contains its PCB
+    int32_t dumptid =
+        ReadSignedIntegerFromMemory(FindSymbol("dumptid"), 4, -1, error);
+    lldb::addr_t dumppcb = FindSymbol("dumppcb");
+
+    // stoppcbs is an array of PCBs on all CPUs
+    // each element is of size pcb_size
+    int32_t pcbsize =
+        ReadSignedIntegerFromMemory(FindSymbol("pcb_size"), 4, -1, error);
+    lldb::addr_t stoppcbs = FindSymbol("stoppcbs");
+
+    // from FreeBSD sys/param.h
+    constexpr size_t fbsd_maxcomlen = 19;
+
+    // iterate through a linked list of all processes
+    // allproc is a pointer to the first list element, p_list field
+    // (found at offset_p_list) specifies the next element
+    for (lldb::addr_t proc =
+             ReadPointerFromMemory(FindSymbol("allproc"), error);
+         proc != 0 && proc != LLDB_INVALID_ADDRESS;
+         proc = ReadPointerFromMemory(proc + offset_p_list, error)) {
+      int32_t pid =
+          ReadSignedIntegerFromMemory(proc + offset_p_pid, 4, -1, error);
+      // process' command-line string
+      char comm[fbsd_maxcomlen + 1];
+      ReadCStringFromMemory(proc + offset_p_comm, comm, sizeof(comm), error);
+
+      // iterate through a linked list of all process' threads
+      // the initial thread is found in process' p_threads, subsequent
+      // elements are linked via td_plist field
+      for (lldb::addr_t td =
+               ReadPointerFromMemory(proc + offset_p_threads, error);
+           td != 0; td = ReadPointerFromMemory(td + offset_td_plist, error)) {
+        int32_t tid =
+            ReadSignedIntegerFromMemory(td + offset_td_tid, 4, -1, error);
+        lldb::addr_t pcb_addr =
+            ReadPointerFromMemory(td + offset_td_pcb, error);
+        // whether process was on CPU (-1 if not, otherwise CPU number)
+        int32_t oncpu =
+            ReadSignedIntegerFromMemory(td + offset_td_oncpu, 4, -2, error);
+        // thread name
+        char thread_name[fbsd_maxcomlen + 1];
+        ReadCStringFromMemory(td + offset_td_name, thread_name,
+                              sizeof(thread_name), error);
+
+        // if we failed to read TID, ignore this thread
+        if (tid == -1)
+          continue;
+
+        std::string thread_desc = llvm::formatv("(pid {0}) {1}", pid, comm);
+        if (*thread_name && strcmp(thread_name, comm)) {
+          thread_desc += '/';
+          thread_desc += thread_name;
+        }
+
+        // roughly:
+        // 1. if the thread crashed, its PCB is going to be at "dumppcb"
+        // 2. if the thread was on CPU, its PCB is going to be on the CPU
+        // 3. otherwise, its PCB is in the thread struct
+        if (tid == dumptid) {
+          // NB: dumppcb can be LLDB_INVALID_ADDRESS if reading it failed
+          pcb_addr = dumppcb;
+          thread_desc += " (crashed)";
+        } else if (oncpu != -1) {
+          // if we managed to read stoppcbs and pcb_size, use them to find
+          // the correct PCB
+          if (stoppcbs != LLDB_INVALID_ADDRESS && pcbsize > 0)
+            pcb_addr = stoppcbs + oncpu * pcbsize;
+          else
+            pcb_addr = LLDB_INVALID_ADDRESS;
+          thread_desc += llvm::formatv(" (on CPU {0})", oncpu);
+        }
+
+        ThreadSP thread_sp{
+            new ThreadFreeBSDKernel(*this, tid, pcb_addr, thread_desc)};
+        new_thread_list.AddThread(thread_sp);
+      }
+    }
   } else {
     const uint32_t num_threads = old_thread_list.GetSize(false);
     for (uint32_t i = 0; i < num_threads; ++i)
@@ -163,6 +266,12 @@ DynamicLoader *ProcessFreeBSDKernel::GetDynamicLoader() {
   return m_dyld_up.get();
 }
 
+lldb::addr_t ProcessFreeBSDKernel::FindSymbol(const char *name) {
+  ModuleSP mod_sp = GetTarget().GetExecutableModule();
+  const Symbol *sym = mod_sp->FindFirstSymbolWithNameAndType(ConstString(name));
+  return sym ? sym->GetLoadAddress(&GetTarget()) : LLDB_INVALID_ADDRESS;
+}
+
 #if LLDB_ENABLE_FBSDVMCORE
 
 ProcessFreeBSDKernelFVC::ProcessFreeBSDKernelFVC(lldb::TargetSP target_sp,

lldb/source/Plugins/Process/FreeBSDKernel/ProcessFreeBSDKernel.h

@@ -46,6 +46,8 @@ class ProcessFreeBSDKernel : public lldb_private::PostMortemProcess {
 protected:
   bool DoUpdateThreadList(lldb_private::ThreadList &old_thread_list,
                           lldb_private::ThreadList &new_thread_list) override;
+
+  lldb::addr_t FindSymbol(const char* name);
 };
 
 #endif // LLDB_SOURCE_PLUGINS_PROCESS_FREEBSDKERNEL_PROCESSFREEBSDKERNEL_H

lldb/source/Plugins/Process/FreeBSDKernel/ThreadFreeBSDKernel.cpp

@@ -24,8 +24,10 @@ using namespace lldb;
 using namespace lldb_private;
 
 ThreadFreeBSDKernel::ThreadFreeBSDKernel(Process &process, lldb::tid_t tid,
-                                         lldb::addr_t pcb_addr)
-    : Thread(process, tid), m_pcb_addr(pcb_addr) {}
+                                         lldb::addr_t pcb_addr,
+                                         std::string thread_name)
+    : Thread(process, tid), m_thread_name(std::move(thread_name)),
+      m_pcb_addr(pcb_addr) {}
 
 ThreadFreeBSDKernel::~ThreadFreeBSDKernel() {}
 
@@ -61,9 +63,8 @@ ThreadFreeBSDKernel::CreateRegisterContextForFrame(StackFrame *frame) {
               m_pcb_addr);
       break;
     case llvm::Triple::x86:
-      m_thread_reg_ctx_sp =
-          std::make_shared<RegisterContextFreeBSDKernel_i386>(
-              *this, new RegisterContextFreeBSD_i386(arch), m_pcb_addr);
+      m_thread_reg_ctx_sp = std::make_shared<RegisterContextFreeBSDKernel_i386>(
+          *this, new RegisterContextFreeBSD_i386(arch), m_pcb_addr);
       break;
     case llvm::Triple::x86_64:
       m_thread_reg_ctx_sp =

lldb/source/Plugins/Process/FreeBSDKernel/ThreadFreeBSDKernel.h

@@ -14,7 +14,7 @@
 class ThreadFreeBSDKernel : public lldb_private::Thread {
 public:
   ThreadFreeBSDKernel(lldb_private::Process &process, lldb::tid_t tid,
-                      lldb::addr_t pcb_addr);
+                      lldb::addr_t pcb_addr, std::string thread_name);
 
   ~ThreadFreeBSDKernel() override;
 
@@ -25,10 +25,24 @@ class ThreadFreeBSDKernel : public lldb_private::Thread {
   lldb::RegisterContextSP
   CreateRegisterContextForFrame(lldb_private::StackFrame *frame) override;
 
+  const char *GetName() override {
+    if (m_thread_name.empty())
+      return nullptr;
+    return m_thread_name.c_str();
+  }
+
+  void SetName(const char *name) override {
+    if (name && name[0])
+      m_thread_name.assign(name);
+    else
+      m_thread_name.clear();
+  }
+
 protected:
   bool CalculateStopInfo() override;
 
 private:
+  std::string m_thread_name;
   lldb::RegisterContextSP m_thread_reg_ctx_sp;
   lldb::addr_t m_pcb_addr;
 };