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[lldb] [Process/FreeBSDKernel] List threads in correct order #178306

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Merged
DavidSpickett merged 1 commit into from
Feb 5, 2026
Merged

[lldb] [Process/FreeBSDKernel] List threads in correct order #178306

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32 changes: 21 additions & 11 deletions lldb/source/Plugins/Process/FreeBSDKernel/ProcessFreeBSDKernel.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -162,7 +162,7 @@ bool ProcessFreeBSDKernel::DoUpdateThreadList(ThreadList &old_thread_list,
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
// 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)
Expand All @@ -174,29 +174,39 @@ bool ProcessFreeBSDKernel::DoUpdateThreadList(ThreadList &old_thread_list,
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
// 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
// Iterate through a linked list of all processes. New processes are added
// to the head of this list. Which means that earlier PIDs are actually at
// the end of the list, so we have to walk it backwards. First collect all
// the processes in the list order.
std::vector<lldb::addr_t> process_addrs;
for (lldb::addr_t proc =
ReadPointerFromMemory(FindSymbol("allproc"), error);
proc != 0 && proc != LLDB_INVALID_ADDRESS;
proc = ReadPointerFromMemory(proc + offset_p_list, error)) {
process_addrs.push_back(proc);
}

// Processes are in the linked list in descending PID order, so we must walk
// them in reverse to get ascending PID order.
for (auto proc_it = process_addrs.rbegin(); proc_it != process_addrs.rend();
++proc_it) {
lldb::addr_t proc = *proc_it;
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
// 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 =
Expand All @@ -214,7 +224,7 @@ bool ProcessFreeBSDKernel::DoUpdateThreadList(ThreadList &old_thread_list,
ReadCStringFromMemory(td + offset_td_name, thread_name,
sizeof(thread_name), error);

// if we failed to read TID, ignore this thread
// If we failed to read TID, ignore this thread.
if (tid == -1)
continue;

Expand All @@ -224,7 +234,7 @@ bool ProcessFreeBSDKernel::DoUpdateThreadList(ThreadList &old_thread_list,
thread_desc += thread_name;
}

// roughly:
// 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
Expand All @@ -233,8 +243,8 @@ bool ProcessFreeBSDKernel::DoUpdateThreadList(ThreadList &old_thread_list,
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 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
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