Re: PPC KGDB changes and some help?

[Tom Rini <trini@kernel.crashing.org>]

On Mon, Jan 26, 2004 at 01:27:35PM -0800, George Anzinger wrote:
> 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?

You get:
- kgdb_breakpoint => debugger_bpt : This is how the various PPC codes
  drop you into KGDB.
- kgdb_iabr_match => debugger_iabr_match : Called from
  InstructionBreakpoint, exception.
- kgdb_dabr_match => debugger_dabr_match : Called from do_page_fault,
  this is a Data Access Breakpoint Register match.

So we need at least 2 for the KGDB side of things (prototypes) and 3
just to make it clear.

-- 
Tom Rini
http://gate.crashing.org/~trini/