1 files changed, 77 insertions, 0 deletions
diff --git a/sys/tools/gdb/pcpu.py b/sys/tools/gdb/pcpu.py
new file mode 100644
index 000000000000..aadc4b2d42df
--- /dev/null
+++ b/sys/tools/gdb/pcpu.py
@@ -0,0 +1,77 @@
+#
+# Copyright (c) 2025 Mark Johnston <markj@FreeBSD.org>
+#
+# SPDX-License-Identifier: BSD-2-Clause
+#
+
+import gdb
+from freebsd import *
+
+class pcpu(gdb.Function):
+    """
+    Register a function to lookup PCPU and DPCPU variables by name.
+
+    To look up the value of the PCPU field foo on CPU n, use
+    $PCPU("foo", n).  This works for DPCPU fields too.  If the CPU ID is
+    omitted, and the currently selected thread is on-CPU, that CPU is
+    used, otherwise an error is raised.
+    """
+    def __init__(self):
+        super(pcpu, self).__init__("PCPU")
+
+    def invoke(self, field, cpuid=-1):
+        if cpuid == -1:
+            cpuid = tdfind(gdb.selected_thread().ptid[2])['td_oncpu']
+            if cpuid == -1:
+                raise gdb.error("Currently selected thread is off-CPU")
+            if cpuid < 0 or cpuid > symval("mp_maxid"):
+                raise gdb.error(f"Currently selected on invalid CPU {cpuid}")
+        pcpu = symval("cpuid_to_pcpu")[cpuid]
+
+        # Are we dealing with a PCPU or DPCPU field?
+        field = field.string()
+        for f in gdb.lookup_type("struct pcpu").fields():
+            if f.name == "pc_" + field:
+                return pcpu["pc_" + field]
+
+        def uintptr_t(val):
+            return val.cast(gdb.lookup_type("uintptr_t"))
+
+        # We're dealing with a DPCPU field.  This is handled similarly
+        # to VNET symbols, see vnet.py for comments.
+        pcpu_base = pcpu['pc_dynamic']
+        pcpu_entry = symval("pcpu_entry_" + field)
+        pcpu_entry_addr = uintptr_t(pcpu_entry.address)
+
+        for lf in linker_file_foreach():
+            block = gdb.block_for_pc(lf['ops']['cls']['methods'][0]['func'])
+            elf_file_t = gdb.lookup_type("elf_file_t", block).target()
+            ef = lf.cast(elf_file_t)
+
+            file_type = lf['ops']['cls']['name'].string()
+            if file_type == "elf64":
+                start = uintptr_t(ef['pcpu_start'])
+                if start == 0:
+                    continue
+                end = uintptr_t(ef['pcpu_stop'])
+                base = uintptr_t(ef['pcpu_base'])
+            elif file_type == "elf64_obj":
+                for i in range(ef['nprogtab']):
+                    pe = ef['progtab'][i]
+                    if pe['name'].string() == "set_pcpu":
+                        start = uintptr_t(pe['origaddr'])
+                        end = start + uintptr_t(pe['size'])
+                        base = uintptr_t(pe['addr'])
+                        break
+                else:
+                    continue
+            else:
+                path = lf['pathname'].string()
+                raise gdb.error(f"{path} has unexpected linker file type {file_type}")
+
+            if pcpu_entry_addr >= start and pcpu_entry_addr < end:
+                obj = gdb.Value(pcpu_base + pcpu_entry_addr - start + base)
+                return obj.cast(pcpu_entry.type.pointer()).dereference()
+
+# Register with gdb.
+pcpu()