Implement db_print_backtrace() if DDB is compiled into the kernel. This

MD function is just a wrapper around db_stack_trace_cmd() that prints out
a backtrace of curthread.  Currently, this function is only implemented
on i386 and alpha (and the alpha version isn't quite tested yet, will do
that in a bit).  Other changes:

- For i386, fix a bug in the raw frame address case.  The eip we extract
  from the passed in frame address does not match the frame we received.
  Thus, instead of printing a bogus frame with the wrong eip, go ahead
  and advance frame down to the same frame as the eip we are using.
- For alpha, attempt to add a way of doing a raw trace for alpha.  Instead
  of passing a frame address in 'addr', pass in a pointer to a structure
  containing PC and KSP and use those to start the backtrace.  The alpha
  db_print_backtrace() uses asm to read in the current PC and KSP values
  into such a request.

Tested on:	i386
Requested by:	many

1 files changed, 25 insertions, 2 deletions

diff --git a/sys/alpha/alpha/db_trace.c b/sys/alpha/alpha/db_trace.c
index f84d1b9..b8a200c 100644
--- a/sys/alpha/alpha/db_trace.c
+++ b/sys/alpha/alpha/db_trace.c
@@ -60,6 +60,11 @@
 #include <ddb/db_output.h>
 #include <alpha/alpha/db_instruction.h>
 
+struct trace_request {
+	register_t ksp;
+	register_t pc;
+};
+
 /*
  * Information about the `standard' Alpha function prologue.
  */
@@ -260,8 +265,16 @@ db_stack_trace_cmd(db_expr_t addr, boolean_t have_addr, db_expr_t count, char *m
 			frame = addr;
 		}
 	} else {
-		db_printf("alpha trace requires known PC =eject=\n");
-		return;
+		struct trace_request *tr;
+
+		tr = (struct trace_request *)addr;
+		if (tr->ksp >= KERNBASE && tr->pc >= KERNBASE) {
+			db_printf("alpha trace requires known PC =eject=\n");
+			return;
+		}
+		callpc = tr->pc;
+		addr = tr->ksp;
+		frame = addr;
 	}
 
 	while (count--) {
@@ -377,7 +390,17 @@ db_stack_trace_cmd(db_expr_t addr, boolean_t have_addr, db_expr_t count, char *m
 	}
 }
 
+void
+db_stack_trace_cmd(void)
+{
+	struct trace_request tr;
 
+	__asm __volatile(
+		"	stq sp,%0 \n"
+		"	stq pc,%1 \n"
+		: "=r" (tr.ksp), "=r" (tr.pc));
+	db_stack_trace_cmd(&tr, 1, -1, NULL);
+}
 
 int
 db_md_set_watchpoint(addr, size)