Index: sys/amd64/include/pcb.h
===================================================================
--- sys/amd64/include/pcb.h
+++ sys/amd64/include/pcb.h
@@ -44,15 +44,19 @@
 #include <machine/segments.h>
 
 #ifdef __amd64__
+/*
+ * NB: The fields marked with (*) are used by kernel debuggers.  Their
+ * ABI should be preserved.
+ */
 struct pcb {
-	register_t	pcb_r15;
-	register_t	pcb_r14;
-	register_t	pcb_r13;
-	register_t	pcb_r12;
-	register_t	pcb_rbp;
-	register_t	pcb_rsp;
-	register_t	pcb_rbx;
-	register_t	pcb_rip;
+	register_t	pcb_r15;	/* (*) */
+	register_t	pcb_r14;	/* (*) */
+	register_t	pcb_r13;	/* (*) */
+	register_t	pcb_r12;	/* (*) */
+	register_t	pcb_rbp;	/* (*) */
+	register_t	pcb_rsp;	/* (*) */
+	register_t	pcb_rbx;	/* (*) */
+	register_t	pcb_rip;	/* (*) */
 	register_t	pcb_fsbase;
 	register_t	pcb_gsbase;
 	register_t	pcb_kgsbase;
Index: sys/i386/include/pcb.h
===================================================================
--- sys/i386/include/pcb.h
+++ sys/i386/include/pcb.h
@@ -44,13 +44,17 @@
 #endif
 #include <machine/npx.h>
 
+/*
+ * NB: The fields marked with (*) are used by kernel debuggers.  Their
+ * ABI should be preserved.
+ */
 struct pcb {
-	int	pcb_edi;
-	int	pcb_esi;
-	int	pcb_ebp;
-	int	pcb_esp;
-	int	pcb_ebx;
-	int	pcb_eip;
+	int	pcb_edi;	/* (*) */
+	int	pcb_esi;	/* (*) */
+	int	pcb_ebp;	/* (*) */
+	int	pcb_esp;	/* (*) */
+	int	pcb_ebx;	/* (*) */
+	int	pcb_eip;	/* (*) */
 	struct segment_descriptor pcb_fsd;
 	struct segment_descriptor pcb_gsd;
 	int	pcb_ds;
Index: sys/kern/kern_linker.c
===================================================================
--- sys/kern/kern_linker.c
+++ sys/kern/kern_linker.c
@@ -70,6 +70,12 @@
     &kld_debug, 0, "Set various levels of KLD debug");
 #endif
 
+/* These variables are used by kernel debuggers to enumerate loaded files. */
+const int kld_off_address = offsetof(struct linker_file, address);
+const int kld_off_filename = offsetof(struct linker_file, filename);
+const int kld_off_pathname = offsetof(struct linker_file, pathname);
+const int kld_off_next = offsetof(struct linker_file, link.tqe_next);
+
 /*
  * static char *linker_search_path(const char *name, struct mod_depend
  * *verinfo);
Index: sys/kern/kern_mib.c
===================================================================
--- sys/kern/kern_mib.c
+++ sys/kern/kern_mib.c
@@ -580,6 +580,11 @@
 SYSCTL_INT(_debug_sizeof, OID_AUTO, kinfo_proc, CTLFLAG_RD,
     SYSCTL_NULL_INT_PTR, sizeof(struct kinfo_proc), "sizeof(struct kinfo_proc)");
 
+/* Used by kernel debuggers. */
+const int pcb_size = sizeof(struct pcb);
+SYSCTL_INT(_debug_sizeof, OID_AUTO, pcb, CTLFLAG_RD,
+    SYSCTL_NULL_INT_PTR, sizeof(struct pcb), "sizeof(struct pcb)");
+
 /* XXX compatibility, remove for 6.0 */
 #include <sys/imgact.h>
 #include <sys/imgact_elf.h>
Index: sys/kern/kern_proc.c
===================================================================
--- sys/kern/kern_proc.c
+++ sys/kern/kern_proc.c
@@ -139,6 +139,21 @@
 struct mtx ppeers_lock;
 uma_zone_t proc_zone;
 
+/*
+ * The offset of various fields in struct proc and struct thread.
+ * These are used by kernel debuggers to enumerate kernel threads and
+ * processes.
+ */
+const int proc_off_p_pid = offsetof(struct proc, p_pid);
+const int proc_off_p_comm = offsetof(struct proc, p_comm);
+const int proc_off_p_list = offsetof(struct proc, p_list);
+const int proc_off_p_threads = offsetof(struct proc, p_threads);
+const int thread_off_td_tid = offsetof(struct thread, td_tid);
+const int thread_off_td_name = offsetof(struct thread, td_name);
+const int thread_off_td_oncpu = offsetof(struct thread, td_oncpu);
+const int thread_off_td_pcb = offsetof(struct thread, td_pcb);
+const int thread_off_td_plist = offsetof(struct thread, td_plist);
+
 int kstack_pages = KSTACK_PAGES;
 SYSCTL_INT(_kern, OID_AUTO, kstack_pages, CTLFLAG_RD, &kstack_pages, 0,
     "Kernel stack size in pages");
Index: sys/vm/vm_kern.c
===================================================================
--- sys/vm/vm_kern.c
+++ sys/vm/vm_kern.c
@@ -94,6 +94,9 @@
 const void *zero_region;
 CTASSERT((ZERO_REGION_SIZE & PAGE_MASK) == 0);
 
+/* NB: Used by kernel debuggers. */
+const u_long vm_maxuser_address = VM_MAXUSER_ADDRESS;
+
 SYSCTL_ULONG(_vm, OID_AUTO, min_kernel_address, CTLFLAG_RD,
     SYSCTL_NULL_ULONG_PTR, VM_MIN_KERNEL_ADDRESS, "Min kernel address");