MFC 290728:

Export various helper variables describing the layout and size of
certain kernel structures for use by debuggers. This mostly aids
in examining cores from a kernel without debug symbols as a debugger
can infer these values if debug symbols are available.

One set of variables describes the layout of 'struct linker_file' to
walk the list of loaded kernel modules.

A second set of variables describes the layout of 'struct proc' and
'struct thread' to walk the list of processes in the kernel and the
threads in each process.

The 'pcb_size' variable is used to index into the stoppcbs[] array.

The 'vm_maxuser_address' is used to distinguish kernel virtual addresses
from user addresses. This doesn't have to be perfect, and
'vm_maxuser_address' is a cheap and simple way to differentiate kernel
pointers from simple values like TIDs and PIDs.

While here, annotate the fields in struct pcb used by kgdb on amd64
and i386 to note that their ABI should be preserved.  Annotations for
other platforms will be added in the future.

1 files changed, 12 insertions, 8 deletions

diff --git a/sys/amd64/include/pcb.h b/sys/amd64/include/pcb.h
index 4bf9a4f..3f8d4c7 100644
--- a/sys/amd64/include/pcb.h
+++ b/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;