Re: PPC KGDB changes and some help?

[George Anzinger <george@mvista.com>]

Tom Rini wrote:
> On Fri, Jan 23, 2004 at 03:38:39PM -0800, George Anzinger wrote:
> 
>>Tom Rini wrote:
>>
>>>On Thu, Jan 22, 2004 at 11:05:55AM -0700, Tom Rini wrote:
>>>[snip]
>>>
>>>
>>>>First up:
>>>>We need to call flush_instruction_cache() on a 'c' or 's' command.
>>>>arch/ppc/kernel/ppc-stub.c |   19 ++++++-------------
>>>>1 files changed, 6 insertions(+), 13 deletions(-)
>>>
>>>
>>>On tpo of this patch, there's the following:
>>>Put back some code to figure out what signal we're dealing with.
>>>
>>>arch/ppc/kernel/ppc-stub.c |   63 
>>>++++++++++++++++++++++++++++++++++++++++++---
>>>1 files changed, 60 insertions(+), 3 deletions(-)
>>>--- 1.15/arch/ppc/kernel/ppc-stub.c	Thu Jan 22 10:53:06 2004
>>>+++ edited/arch/ppc/kernel/ppc-stub.c	Fri Jan 23 15:43:10 2004
>>>@@ -3,6 +3,7 @@
>>> *
>>> * PowerPC-specific bits to work with the common KGDB stub.
>>> *
>>>+ * 1998 (c) Michael AK Tesch (tesch@cs.wisc.edu)
>>> * 2003 (c) TimeSys Corporation
>>> * 2004 (c) MontaVista Software, Inc.
>>> * This file is licensed under the terms of the GNU General Public License
>>>@@ -19,13 +20,69 @@
>>>#include <asm/processor.h>
>>>#include <asm/machdep.h>
>>>
>>>+/* Convert the hardware trap type code to a unix signal number. */
>>>+/*
>>>+ * This table contains the mapping between PowerPC hardware trap types, 
>>>and
>>>+ * signals, which are primarily what GDB understands.
>>>+ */
>>>+static struct hard_trap_info
>>>+{
>>>+	unsigned int tt;		/* Trap type code for powerpc */
>>>+	unsigned char signo;		/* Signal that we map this trap into 
>>>*/
>>>+} hard_trap_info[] = {
>>>+#if defined(CONFIG_40x)
>>>+	{ 0x100, SIGINT  },		/* critical input interrupt */
>>>+	{ 0x200, SIGSEGV },		/* machine check */
>>>+	{ 0x300, SIGSEGV },		/* data storage */
>>>+	{ 0x400, SIGBUS  },		/* instruction storage */
>>>+	{ 0x500, SIGINT  },		/* interrupt */
>>>+	{ 0x600, SIGBUS  },		/* alignment */
>>>+	{ 0x700, SIGILL  },		/* program */
>>>+	{ 0x800, SIGILL  },		/* reserved */
>>>+	{ 0x900, SIGILL  },		/* reserved */
>>>+	{ 0xa00, SIGILL  },		/* reserved */
>>>+	{ 0xb00, SIGILL  },		/* reserved */
>>>+	{ 0xc00, SIGCHLD },		/* syscall */
>>>+	{ 0xd00, SIGILL  },		/* reserved */
>>>+	{ 0xe00, SIGILL  },		/* reserved */
>>>+	{ 0xf00, SIGILL  },		/* reserved */
>>>+	{ 0x2000, SIGTRAP},		/* debug */
>>>+#else
>>>+	{ 0x200, SIGSEGV },		/* machine check */
>>>+	{ 0x300, SIGSEGV },		/* address error (store) */
>>>+	{ 0x400, SIGBUS },		/* instruction bus error */
>>>+	{ 0x500, SIGINT },		/* interrupt */
>>>+	{ 0x600, SIGBUS },		/* alingment */
>>>+	{ 0x700, SIGTRAP },		/* breakpoint trap */
>>>+	{ 0x800, SIGFPE },		/* fpu unavail */
>>>+	{ 0x900, SIGALRM },		/* decrementer */
>>>+	{ 0xa00, SIGILL },		/* reserved */
>>>+	{ 0xb00, SIGILL },		/* reserved */
>>>+	{ 0xc00, SIGCHLD },		/* syscall */
>>>+	{ 0xd00, SIGTRAP },		/* single-step/watch */
>>>+	{ 0xe00, SIGFPE },		/* fp assist */
>>>+#endif
>>>+	{ 0, 0}				/* Must be last */
>>>+};
>>>+
>>>+static int computeSignal(unsigned int tt)
>>>+{
>>>+	struct hard_trap_info *ht;
>>>+
>>>+	for (ht = hard_trap_info; ht->tt && ht->signo; ht++)
>>>+		if (ht->tt == tt)
>>>+			return ht->signo;
>>>+
>>>+	return SIGHUP; /* default for things we don't know about */
>>>+}
>>>+
>>>/*
>>> * Routines
>>> */
>>>static void
>>>kgdb_debugger(struct pt_regs *regs)
>>>{
>>>-	(*linux_debug_hook) (0, 0, 0, regs);
>>>+	(*linux_debug_hook) (0, computeSignal(regs->trap), 0, regs);
>>>	return;
>>>}
>>>
>>>@@ -52,14 +109,14 @@
>>>int
>>>kgdb_iabr_match(struct pt_regs *regs)
>>>{
>>>-	(*linux_debug_hook) (0, 0, 0, regs);
>>>+	(*linux_debug_hook) (0, computeSignal(regs->trap), 0, regs);
>>>	return 1;
>>>}
>>>
>>>int
>>>kgdb_dabr_match(struct pt_regs *regs)
>>>{
>>>-	(*linux_debug_hook) (0, 0, 0, regs);
>>>+	(*linux_debug_hook) (0, computeSignal(regs->trap), 0, regs);
>>>	return 1;
>>>}
>>>
>>>
>>>Now, not being as well versed in all of the debugging infos that can be
>>>passed around, it sounds like this patch could be dropped in the future
>>>for a cleaner method using some of the dwarf2 bits being talked about.
>>>But I don't know, and clarification and pointers (if so) to how to do
>>>this would be appreciated.
>>
>>I am not sure what this buys you.  I don't think dwarf2 will help here.
> 
> 
> OK.
> 
> 
>>There is a real danger of passing signal info back to gdb as it will want 
>>to try to deliver the signal which is a non-compute in most kgdbs in the 
>>field.  I did put code in the mm-kgdb to do just this, but usually the 
>>arrival of such a signal (other than SIGTRAP) is the end of the kernel.  
>>All that is left is to read the tea leaves.
> 
> 
> The gdb I've been testing this with knows better than to try and send a
> singal back, so that's not a worry.  The motivation behind doing this
> however is along the lines of "if it ain't broke, don't remove it".  The
> original stub was getting all of this information correctly, so why stop
> doing it?
> 
OK, but I still don't like losing the return address.  Tell me again, why do you 
need three different functions all doing the same thing?


-- 
George Anzinger   george@mvista.com
High-res-timers:  http://sourceforge.net/projects/high-res-timers/
Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml