Add more debugging steps

diff --git a/docs/howtos/HowToDebugVKernels/index.mdwn b/docs/howtos/HowToDebugVKernels/index.mdwn
index 18d347d..05e3e64 100644 (file)
--- a/docs/howtos/HowToDebugVKernels/index.mdwn
+++ b/docs/howtos/HowToDebugVKernels/index.mdwn
@@ -107,7 +107,7 @@ We need to do better this time. Let's break into the kernel _before_ it crashes.
     Breakpoint 1 at 0x80acf43: file ./machine/thread.h, line 83.
     (gdb) 
 
-Next type 'c' in the gdb prompt to resume vkernel execution:
+Next we type 'c' in the gdb prompt to resume vkernel execution:
 
     (gdb) c
     Continuing.
@@ -122,6 +122,22 @@ Gdb stops the execution of vkernel and a message pops up in gdb buffer:
     83          __asm ("movl %%fs:globaldata,%0" : "=r" (gd) : "m"(__mycpu__dummy));
     (gdb) 
 
-We navigate through source code with the 'step' and 'next' gdb commands. They are identical, except that 'step' follows function calls. We 
+We navigate through source code with the 'step' and 'next' gdb commands. They are identical, except that 'step' follows function calls. When we meet this call:
 
-276                     allproc_scan(ktrace_clear_callback, &info);
+    276                     allproc_scan(ktrace_clear_callback, &info);
+
+we 'step' inside it. alloproc_scan() iterates through the process list and applies the ktrace_clear_callback() to each one of them.
+Later we see this:
+
+    347                     if (p->p_tracenode->kn_vp == info->tracenode->kn_vp) {
+
+Here p is a pointer to the current process:
+    (gdb) print p
+    $1 = (struct proc *) 0x57098c00
+
+Let's see if this process is traced:
+    (gdb) print p->p_tracenode
+    $2 = (struct ktrace_node *) 0x0
+    (gdb) 
+
+Oops. There is no trace to a vnode for this process.