[PATCH v3 0/11] KGDB/KDB FIQ (NMI) debugger

[PATCH v3 0/11] KGDB/KDB FIQ (NMI) debugger

[Anton Vorontsov]

Hi all,

I do realize that we're in the middle of the merge window. But maybe
some of you will be bored enough to look into this; and no problem if
you don't feel like it -- I promise to send a brand new shiny v4 after
the merge window, so you won't miss a bit of this new cool stuff. :-)

In v3:

- Per Colin Cross suggestion, added a way to release a debug console for
  normal use.  This is done via 'disable_nmi' command (in the original
  FIQ debugger it was 'console' command). For this I added a new callback
  in the tty ops, and serial drivers have to provide a way to clear its
  interrupts. The patch 'tty/serial/kgdboc: Add and wire up clear_irqs
  callback' explains the concept in details.
- Made the debug entry prompt more shell-like;
- A new knocking mode '-1'. It disables the feature altogether, and thus
  makes it possible to hook KDB entry to a dedicated button.
- The code was rebased on 'v3.5 + kdb kiosk'[1] patches; and for
  convenience it is now available in the following repo:

  	git://git.infradead.org/users/cbou/linux-nmi-kdb.git master

Rationale for this patch set:

These patches introduce KGDB FIQ debugger support. The idea (and some
code, of course) comes from Google's FIQ debugger[2]. There are some
differences (mostly implementation details, feature-wise they're almost
equivalent, or can be made equivalent, if desired).

The FIQ debugger is a facility that can be used to debug situations
when the kernel stuck in uninterruptable sections, e.g. the kernel
infinitely loops or deadlocked in an interrupt or with interrupts
disabled. On some development boards there is even a special NMI
button, which is very useful for debugging weird kernel hangs.

And FIQ is basically an NMI, it has a higher priority than IRQs, and
upon IRQ exception FIQs are not disabled. It is still possible to
disable FIQs (as well as some "NMIs" on other architectures), but via
special means.

So, here FIQs and NMIs are synonyms, but in the code I use NMI term
for arch-independent code, and FIQs for ARM code.

A few years ago KDB wasn't yet ready for production, or even not
well-known, so originally Google implemented its own FIQ debugger
that included its own shell, ring-buffer, commands, dumping,
backtracing logic and whatnot. This is very much like PowerPC's xmon
(arch/powerpc/xmon), except that xmon was there for a decade, so it
even predates KDB.

Anyway, nowadays KGDB/KDB is the cross-platform debugger, and the
only feature that was missing is NMI handling. This is now fixed for
ARM.

There are a few differences comparing to the original (Google's) FIQ
debugger:

- Doing stuff in FIQ context is dangerous, as there we are not allowed
  to cause aborts or faults. In the original FIQ debugger there was a
  "signal" software-induced interrupt, upon exit from FIQ it would fire,
  and we would continue to execute "dangerous" commands from there.

  In KGDB/KDB we don't use signal interrupts. We can do easier:
  set up a breakpoint, continue, and you'll trap into KGDB again
  in a safe context.

  It works for most cases, but I can imagine cases when you can't
  set up a breakpoint. For these cases we'd better introduce a
  KDB command "exit_nmi", that will rise the SW IRQ, after which
  we're allowed to do anything.

- KGDB/KDB FIQ debugger shell is synchronous. In Google's version
  you could have a dedicated shell always running in the FIQ context,
  so when you type something on a serial line, you won't actually cause
  any debugging actions, FIQ would save the characters in its own
  buffer and continue execution normally. But when you hit return key
  after the command, then the command is executed.

  In KGDB/KDB FIQ debugger it is different. Once you enter KGDB, the
  kernel will stop until you instruct it to continue.

  This might look as a drastic change, but it is not. There is actually
  no difference whether you have sync or async shell, or at least I
  couldn't find any use-case where this would matter at all. Anyways,
  it is still possible to do async shell in KDB, just don't see any
  need for this.

- Original FIQ debugger used a custom FIQ vector handling code, w/
  a lot of logic in it. In this approach I'm using the fact that
  FIQs are basically IRQs, except that we there are a bit more
  registers banked, and we can actually trap from the IRQ context.

  But this all does not prevent us from using a simple jump-table
  based approach as used in the generic ARM entry code. So, here
  I just reuse the generic approach.

Note that I test the code on a modelled ARM machine (QEMU Versatile), so
there might be some issues on a real HW, but it works in QEMU tho. :-)

Assuming you have QEMU >= 1.1.0, you can easily play with the code
using ARM/versatile defconfig and command like this:

  qemu-system-arm -nographic -machine versatilepb \
  	-kernel linux/arch/arm/boot/zImage  \
  	-append "console=ttyAMA0 kgdboc=ttyAMA0 kgdb_fiq.enable=1"

Thanks,

--
 arch/arm/Kconfig                            |   19 +++
 arch/arm/common/vic.c                       |   28 +++++
 arch/arm/include/asm/hardware/vic.h         |    2 +
 arch/arm/include/asm/kgdb.h                 |    8 ++
 arch/arm/kernel/Makefile                    |    1 +
 arch/arm/kernel/entry-armv.S                |  169 +------------------------
 arch/arm/kernel/entry-header.S              |  176 ++++++++++++++++++++++++++-
 arch/arm/kernel/kgdb_fiq.c                  |  159 ++++++++++++++++++++++++
 arch/arm/kernel/kgdb_fiq_entry.S            |   76 ++++++++++++
 arch/arm/mach-versatile/Makefile            |    1 +
 arch/arm/mach-versatile/include/mach/irqs.h |    1 +
 arch/arm/mach-versatile/kgdb_fiq.c          |   31 +++++
 drivers/tty/serial/amba-pl011.c             |   13 ++
 drivers/tty/serial/kgdboc.c                 |    9 ++
 drivers/tty/serial/serial_core.c            |   15 +++
 include/linux/kgdb.h                        |   14 +++
 include/linux/serial_core.h                 |    1 +
 include/linux/tty_driver.h                  |    1 +
 kernel/debug/debug_core.c                   |   13 +-
 kernel/debug/kdb/kdb_debugger.c             |    4 +
 kernel/debug/kdb/kdb_main.c                 |   20 +++
 21 files changed, 591 insertions(+), 170 deletions(-)

In v2:

- Per Colin Cross' suggestion, we should not enter the debugger on any
  received byte (this might be a problem when there's a noise on the
  serial line). So there is now an additional patch that implements
  "knocking" to the KDB (either via $3#33 command or return key, this
  is configurable);
- Reworked {enable,select}_fiq/is_fiq callbacks, now multi-mach kernels
  should not be a problem;
- For versatile machines there are run-time checks for proper UART port
  (kernel will scream aloud if out of range port is specified);
- Added some __init annotations;
- Since not every architecture defines FIQ_START, we can't just blindly
  select CONFIG_FIQ symbol. So ARCH_MIGHT_HAVE_FIQ introduced;
- Add !THUMB2_KERNEL dependency for KGDB_FIQ, we don't support Thumb2
  kernels;
- New patch that is used to get rid of LCcralign label in alignment_trap
  macro.

[1] https://lkml.org/lkml/2012/7/26/260
[2] Original Google's FIQ debugger, fiq_* files:
http://android.git.linaro.org/gitweb?p=kernel/common.git;a=tree;f=arch/arm/common;hb=refs/heads/android-3.4
And board support as an example of using it:
http://nv-tegra.nvidia.com/gitweb/?p=linux-2.6.git;a=commitdiff;h=461cb80c16e4e266ab6207a00767b59212148086

-- 
Anton Vorontsov
Email: cbouatmailru@gmail.com

[PATCH 01/11] kernel/debug: Make use of KGDB_REASON_NMI

[Anton Vorontsov]

Currently kernel never set KGDB_REASON_NMI. We do now, when we enter
KGDB/KDB from an NMI.

This is not to be confused with kgdb_nmicallback(), NMI callback is
an entry for the slave CPUs during CPUs roundup, but REASON_NMI is the
entry for the master CPU.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 kernel/debug/kdb/kdb_debugger.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/debug/kdb/kdb_debugger.c b/kernel/debug/kdb/kdb_debugger.c
index 8b68ce7..be7b33b 100644
--- a/kernel/debug/kdb/kdb_debugger.c
+++ b/kernel/debug/kdb/kdb_debugger.c
@@ -12,6 +12,7 @@
 #include <linux/kdb.h>
 #include <linux/kdebug.h>
 #include <linux/export.h>
+#include <linux/hardirq.h>
 #include "kdb_private.h"
 #include "../debug_core.h"
 
@@ -52,6 +53,9 @@ int kdb_stub(struct kgdb_state *ks)
 	if (atomic_read(&kgdb_setting_breakpoint))
 		reason = KDB_REASON_KEYBOARD;
 
+	if (in_nmi())
+		reason = KDB_REASON_NMI;
+
 	for (i = 0, bp = kdb_breakpoints; i < KDB_MAXBPT; i++, bp++) {
 		if ((bp->bp_enabled) && (bp->bp_addr == addr)) {
 			reason = KDB_REASON_BREAK;
-- 
1.7.10.4

[PATCH 02/11] kernel/debug: Mask KGDB NMI upon entry

[Anton Vorontsov]

The new arch callback should manage NMIs that usually cause KGDB to
enter. That is, not all NMIs should be enabled/disabled, but only
those that issue kgdb_handle_exception().

We must mask it as serial-line interrupt can be used as an NMI, so
if the original KGDB-entry cause was say a breakpoint, then every
input to KDB console will cause KGDB to reenter, which we don't want.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 include/linux/kgdb.h      |   13 +++++++++++++
 kernel/debug/debug_core.c |   13 ++++++++++++-
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h
index c4d2fc1..e0c0a2e 100644
--- a/include/linux/kgdb.h
+++ b/include/linux/kgdb.h
@@ -221,6 +221,19 @@ extern int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt);
  */
 extern void kgdb_arch_late(void);
 
+/**
+ *	kgdb_arch_enable_nmi - Enable or disable KGDB-entry NMI
+ *	@on: Flag to either enable or disable an NMI
+ *
+ *	This function manages NMIs that usually cause KGDB to enter. That is,
+ *	not all NMIs should be enabled or disabled, but only those that issue
+ *	kgdb_handle_exception().
+ *
+ *	The call counts disable/enable requests, it returns 1 if NMI has been
+ *	actually enabled after the call, and a value <= 0 if it is still
+ *	disabled.
+ */
+extern int kgdb_arch_enable_nmi(bool on);
 
 /**
  * struct kgdb_arch - Describe architecture specific values.
diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index 0557f24..38b0ab2 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -214,6 +214,11 @@ int __weak kgdb_skipexception(int exception, struct pt_regs *regs)
 	return 0;
 }
 
+int __weak kgdb_arch_enable_nmi(bool on)
+{
+	return 0;
+}
+
 /*
  * Some architectures need cache flushes when we set/clear a
  * breakpoint:
@@ -672,6 +677,9 @@ kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
 {
 	struct kgdb_state kgdb_var;
 	struct kgdb_state *ks = &kgdb_var;
+	int ret;
+
+	kgdb_arch_enable_nmi(0);
 
 	ks->cpu			= raw_smp_processor_id();
 	ks->ex_vector		= evector;
@@ -685,7 +693,10 @@ kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
 	if (kgdb_info[ks->cpu].enter_kgdb != 0)
 		return 0;
 
-	return kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
+	ret = kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
+
+	kgdb_arch_enable_nmi(1);
+	return ret;
 }
 
 int kgdb_nmicallback(int cpu, void *regs)
-- 
1.7.10.4

[PATCH 03/11] kdb: Implement disable_nmi command

[Anton Vorontsov]

This command disables NMI-entry. If NMI source was previously shared with
a serial console ("debug port"), this effectively releases the port from
KDB exclusive use, and makes the console available for normal use.

Of course, NMI can be reenabled, enable_nmi modparam is used for that:

	echo 1 > /sys/module/kdb/parameters/enable_nmi

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 kernel/debug/kdb/kdb_main.c |   20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 3ee92a1..1e9f20e 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -2131,6 +2131,24 @@ static int kdb_dmesg(int argc, const char **argv)
 	return 0;
 }
 #endif /* CONFIG_PRINTK */
+
+static int kdb_disable_nmi(int argc, const char *argv[])
+{
+	kgdb_arch_enable_nmi(0);
+	return 0;
+}
+
+static int kdb_param_enable_nmi(const char *val, const struct kernel_param *kp)
+{
+	kgdb_arch_enable_nmi(1);
+	return 0;
+}
+
+static const struct kernel_param_ops kdb_param_ops_enable_nmi = {
+	.set = kdb_param_enable_nmi,
+};
+module_param_cb(enable_nmi, &kdb_param_ops_enable_nmi, NULL, 0600);
+
 /*
  * kdb_cpu - This function implements the 'cpu' command.
  *	cpu	[<cpunum>]
@@ -2873,6 +2891,8 @@ static void __init kdb_inittab(void)
 	kdb_register_flags("dmesg", kdb_dmesg, "[lines]",
 	  "Display syslog buffer", 0, KDB_SAFE);
 #endif
+	kdb_register_flags("disable_nmi", kdb_disable_nmi, "",
+	  "Disable NMI entry to KDB", 0, KDB_SAFE);
 	kdb_register_flags("defcmd", kdb_defcmd, "name \"usage\" \"help\"",
 	  "Define a set of commands, down to endefcmd", 0, KDB_SAFE);
 	kdb_register_flags("kill", kdb_kill, "<-signal> <pid>",
-- 
1.7.10.4

[PATCH 04/11] tty/serial/kgdboc: Add and wire up clear_irqs callback

[Anton Vorontsov]

This patch implements a new callback: clear_irqs. It is used for the
cases when KDB-entry (e.g. NMI) and KDB IO (e.g. serial port) shares
the same interrupt. To get the idea, let's take some real example (ARM
machine): we have a serial port which interrupt is routed to an NMI,
and the interrupt is used to enter KDB. Once there is some activity on
the serial port, the CPU receives NMI exception, and we fall into KDB
shell. So, it is our "debug console", and it is able to interrupt (and
thus debug) even IRQ handlers themselves.

When used that way, the interrupt never reaches serial driver's IRQ
handler routine, which means that serial driver will not silence the
interrupt. NMIs behaviour are quite arch-specific, and we can't assume
that we can use them as ordinary IRQs, e.g. on some arches (like ARM)
we can't handle data aborts, the behaviour is undefined then. So we
can't just handle execution to serial driver's IRQ handler from the
NMI context once we're done with KDB (plus this would defeat the
debugger's purpose: we want the NMI handler be as simple as possible,
so it will have less chances to hang).

So, given that have to deal with it somehow, we have two options:

1. Implement something that clears the interrupt;
2. Implement a whole new concept of grabbing tty for exclusive KDB use,
   plus implement mask/unmask callbacks, i.e.:
   - Since consoles might use ttys w/o opending them, we would have
     to make kdb respect CON_ENABLED flag (maybe a good idea to do it
     anyway);
   - Add 'bool exclusive' argument to tty_find_polling_driver(), if set
     to 1, the function will refuse to return an already tty; and will
     use the flag in tty_reopen() to not allow multiple users (there are
     already checks for pty masters, which are "open once" ttys);
   - Once we got the tty exclusively, we would need to call some new
     uart->mask_all_but_rx_interrupts call before we want to use the
     port for NMI/KDB, and unmask_all_but_rx_interrupts after we're
     done with it.

The second option is obviously more complex, needlessly so, and less
generic. So I went with the first one: we just consume all the interrupts.
The tty becomes silently unusable for the rest of the world when we use
it with KDB; but once we reroute the serial IRQ source back from NMI to
an ordinary IRQ (in KDB this can be done with 'disable_nmi' command), it
will behave as normal.

p.s. Since the callback is so far used only by polling user, we place
it under the appropriate #ifdef.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 drivers/tty/serial/kgdboc.c      |    9 +++++++++
 drivers/tty/serial/serial_core.c |   15 +++++++++++++++
 include/linux/kgdb.h             |    1 +
 include/linux/serial_core.h      |    1 +
 include/linux/tty_driver.h       |    1 +
 5 files changed, 27 insertions(+)

diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
index 2b42a01..178e62c 100644
--- a/drivers/tty/serial/kgdboc.c
+++ b/drivers/tty/serial/kgdboc.c
@@ -227,6 +227,14 @@ static int kgdboc_get_char(void)
 						kgdb_tty_line);
 }
 
+static void kgdboc_clear_irqs(void)
+{
+	if (!kgdb_tty_driver)
+		return;
+	if (kgdb_tty_driver->ops->clear_irqs)
+		kgdb_tty_driver->ops->clear_irqs(kgdb_tty_driver, kgdb_tty_line);
+}
+
 static void kgdboc_put_char(u8 chr)
 {
 	if (!kgdb_tty_driver)
@@ -298,6 +306,7 @@ static struct kgdb_io kgdboc_io_ops = {
 	.name			= "kgdboc",
 	.read_char		= kgdboc_get_char,
 	.write_char		= kgdboc_put_char,
+	.clear_irqs		= kgdboc_clear_irqs,
 	.pre_exception		= kgdboc_pre_exp_handler,
 	.post_exception		= kgdboc_post_exp_handler,
 };
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 246b823..89c4093 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -2154,6 +2154,20 @@ static void uart_poll_put_char(struct tty_driver *driver, int line, char ch)
 	port = state->uart_port;
 	port->ops->poll_put_char(port, ch);
 }
+
+static void uart_clear_irqs(struct tty_driver *driver, int line)
+{
+	struct uart_driver *drv = driver->driver_state;
+	struct uart_state *state = drv->state + line;
+	struct uart_port *port;
+
+	if (!state || !state->uart_port)
+		return;
+
+	port = state->uart_port;
+	if (port->ops->clear_irqs)
+		port->ops->clear_irqs(port);
+}
 #endif
 
 static const struct tty_operations uart_ops = {
@@ -2186,6 +2200,7 @@ static const struct tty_operations uart_ops = {
 	.poll_init	= uart_poll_init,
 	.poll_get_char	= uart_poll_get_char,
 	.poll_put_char	= uart_poll_put_char,
+	.clear_irqs	= uart_clear_irqs,
 #endif
 };
 
diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h
index e0c0a2e..f695b26 100644
--- a/include/linux/kgdb.h
+++ b/include/linux/kgdb.h
@@ -285,6 +285,7 @@ struct kgdb_io {
 	const char		*name;
 	int			(*read_char) (void);
 	void			(*write_char) (u8);
+	void			(*clear_irqs) (void);
 	void			(*flush) (void);
 	int			(*init) (void);
 	void			(*pre_exception) (void);
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 65db992..081d300 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -275,6 +275,7 @@ struct uart_ops {
 #ifdef CONFIG_CONSOLE_POLL
 	void	(*poll_put_char)(struct uart_port *, unsigned char);
 	int		(*poll_get_char)(struct uart_port *);
+	void	(*clear_irqs)(struct uart_port *);
 #endif
 };
 
diff --git a/include/linux/tty_driver.h b/include/linux/tty_driver.h
index 6e6dbb7..94b14cd 100644
--- a/include/linux/tty_driver.h
+++ b/include/linux/tty_driver.h
@@ -287,6 +287,7 @@ struct tty_operations {
 	int (*poll_init)(struct tty_driver *driver, int line, char *options);
 	int (*poll_get_char)(struct tty_driver *driver, int line);
 	void (*poll_put_char)(struct tty_driver *driver, int line, char ch);
+	void (*clear_irqs)(struct tty_driver *driver, int line);
 #endif
 	const struct file_operations *proc_fops;
 };
-- 
1.7.10.4

[PATCH 05/11] tty/serial/amba-pl011: Implement clear_irqs callback

[Anton Vorontsov]

It's all pretty straightforward, except for TXIM interrupt. The interrupt
has meaning "ready to transmit", so it's almost always raised, and the
only way to silence it is to mask it. But that's OK, ops->start_tx will
unmask it.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 drivers/tty/serial/amba-pl011.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index c17923e..378d26b 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1308,6 +1308,18 @@ static void pl010_put_poll_char(struct uart_port *port,
 	writew(ch, uap->port.membase + UART01x_DR);
 }
 
+static void pl010_clear_irqs(struct uart_port *port)
+{
+	struct uart_amba_port *uap = (struct uart_amba_port *)port;
+	unsigned char __iomem *regs = uap->port.membase;
+
+	writew(readw(regs + UART011_MIS), regs + UART011_ICR);
+	/*
+	 * There is no way to clear TXIM, this is "ready to transmit IRQ", so
+	 * we simply mask it. ops->start_tx will unmask it.
+	 */
+	writew(readw(regs + UART011_IMSC) & ~UART011_TXIM, regs + UART011_IMSC);
+}
 #endif /* CONFIG_CONSOLE_POLL */
 
 static int pl011_startup(struct uart_port *port)
@@ -1698,6 +1710,7 @@ static struct uart_ops amba_pl011_pops = {
 #ifdef CONFIG_CONSOLE_POLL
 	.poll_get_char = pl010_get_poll_char,
 	.poll_put_char = pl010_put_poll_char,
+	.clear_irqs    = pl010_clear_irqs,
 #endif
 };
 
-- 
1.7.10.4

[PATCH 06/11] ARM: Move some macros from entry-armv to entry-header

[Anton Vorontsov]

Just move the macros into header file as we would want to use them for
KGDB FIQ entry code.

The following macros were moved:

 - svc_entry
 - usr_entry
 - kuser_cmpxchg_check
 - vector_stub

To make kuser_cmpxchg_check actually work across different files, we
also have to make kuser_cmpxchg64_fixup global.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 arch/arm/kernel/entry-armv.S   |  167 +--------------------------------------
 arch/arm/kernel/entry-header.S |  170 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 171 insertions(+), 166 deletions(-)

diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 0d1851c..6aeb9b8 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -136,57 +136,6 @@ common_invalid:
 	b	bad_mode
 ENDPROC(__und_invalid)
 
-/*
- * SVC mode handlers
- */
-
-#if defined(CONFIG_AEABI) && (__LINUX_ARM_ARCH__ >= 5)
-#define SPFIX(code...) code
-#else
-#define SPFIX(code...)
-#endif
-
-	.macro	svc_entry, stack_hole=0
- UNWIND(.fnstart		)
- UNWIND(.save {r0 - pc}		)
-	sub	sp, sp, #(S_FRAME_SIZE + \stack_hole - 4)
-#ifdef CONFIG_THUMB2_KERNEL
- SPFIX(	str	r0, [sp]	)	@ temporarily saved
- SPFIX(	mov	r0, sp		)
- SPFIX(	tst	r0, #4		)	@ test original stack alignment
- SPFIX(	ldr	r0, [sp]	)	@ restored
-#else
- SPFIX(	tst	sp, #4		)
-#endif
- SPFIX(	subeq	sp, sp, #4	)
-	stmia	sp, {r1 - r12}
-
-	ldmia	r0, {r3 - r5}
-	add	r7, sp, #S_SP - 4	@ here for interlock avoidance
-	mov	r6, #-1			@  ""  ""      ""       ""
-	add	r2, sp, #(S_FRAME_SIZE + \stack_hole - 4)
- SPFIX(	addeq	r2, r2, #4	)
-	str	r3, [sp, #-4]!		@ save the "real" r0 copied
-					@ from the exception stack
-
-	mov	r3, lr
-
-	@
-	@ We are now ready to fill in the remaining blanks on the stack:
-	@
-	@  r2 - sp_svc
-	@  r3 - lr_svc
-	@  r4 - lr_<exception>, already fixed up for correct return/restart
-	@  r5 - spsr_<exception>
-	@  r6 - orig_r0 (see pt_regs definition in ptrace.h)
-	@
-	stmia	r7, {r2 - r6}
-
-#ifdef CONFIG_TRACE_IRQFLAGS
-	bl	trace_hardirqs_off
-#endif
-	.endm
-
 	.align	5
 __dabt_svc:
 	svc_entry
@@ -328,71 +277,8 @@ ENDPROC(__pabt_svc)
 
 /*
  * User mode handlers
- *
- * EABI note: sp_svc is always 64-bit aligned here, so should S_FRAME_SIZE
  */
 
-#if defined(CONFIG_AEABI) && (__LINUX_ARM_ARCH__ >= 5) && (S_FRAME_SIZE & 7)
-#error "sizeof(struct pt_regs) must be a multiple of 8"
-#endif
-
-	.macro	usr_entry
- UNWIND(.fnstart	)
- UNWIND(.cantunwind	)	@ don't unwind the user space
-	sub	sp, sp, #S_FRAME_SIZE
- ARM(	stmib	sp, {r1 - r12}	)
- THUMB(	stmia	sp, {r0 - r12}	)
-
-	ldmia	r0, {r3 - r5}
-	add	r0, sp, #S_PC		@ here for interlock avoidance
-	mov	r6, #-1			@  ""  ""     ""        ""
-
-	str	r3, [sp]		@ save the "real" r0 copied
-					@ from the exception stack
-
-	@
-	@ We are now ready to fill in the remaining blanks on the stack:
-	@
-	@  r4 - lr_<exception>, already fixed up for correct return/restart
-	@  r5 - spsr_<exception>
-	@  r6 - orig_r0 (see pt_regs definition in ptrace.h)
-	@
-	@ Also, separately save sp_usr and lr_usr
-	@
-	stmia	r0, {r4 - r6}
- ARM(	stmdb	r0, {sp, lr}^			)
- THUMB(	store_user_sp_lr r0, r1, S_SP - S_PC	)
-
-	@
-	@ Enable the alignment trap while in kernel mode
-	@
-	alignment_trap r0
-
-	@
-	@ Clear FP to mark the first stack frame
-	@
-	zero_fp
-
-#ifdef CONFIG_IRQSOFF_TRACER
-	bl	trace_hardirqs_off
-#endif
-	.endm
-
-	.macro	kuser_cmpxchg_check
-#if !defined(CONFIG_CPU_32v6K) && !defined(CONFIG_NEEDS_SYSCALL_FOR_CMPXCHG)
-#ifndef CONFIG_MMU
-#warning "NPTL on non MMU needs fixing"
-#else
-	@ Make sure our user space atomic helper is restarted
-	@ if it was interrupted in a critical region.  Here we
-	@ perform a quick test inline since it should be false
-	@ 99.9999% of the time.  The rest is done out of line.
-	cmp	r4, #TASK_SIZE
-	blhs	kuser_cmpxchg64_fixup
-#endif
-#endif
-	.endm
-
 	.align	5
 __dabt_usr:
 	usr_entry
@@ -813,6 +699,7 @@ __kuser_cmpxchg64:				@ 0xffff0f60
 	ldmfd	sp!, {r4, r5, r6, pc}
 
 	.text
+	.global kuser_cmpxchg64_fixup
 kuser_cmpxchg64_fixup:
 	@ Called from kuser_cmpxchg_fixup.
 	@ r4 = address of interrupted insn (must be preserved).
@@ -943,58 +830,6 @@ __kuser_helper_end:
 
  THUMB(	.thumb	)
 
-/*
- * Vector stubs.
- *
- * This code is copied to 0xffff0200 so we can use branches in the
- * vectors, rather than ldr's.  Note that this code must not
- * exceed 0x300 bytes.
- *
- * Common stub entry macro:
- *   Enter in IRQ mode, spsr = SVC/USR CPSR, lr = SVC/USR PC
- *
- * SP points to a minimal amount of processor-private memory, the address
- * of which is copied into r0 for the mode specific abort handler.
- */
-	.macro	vector_stub, name, mode, correction=0
-	.align	5
-
-vector_\name:
-	.if \correction
-	sub	lr, lr, #\correction
-	.endif
-
-	@
-	@ Save r0, lr_<exception> (parent PC) and spsr_<exception>
-	@ (parent CPSR)
-	@
-	stmia	sp, {r0, lr}		@ save r0, lr
-	mrs	lr, spsr
-	str	lr, [sp, #8]		@ save spsr
-
-	@
-	@ Prepare for SVC32 mode.  IRQs remain disabled.
-	@
-	mrs	r0, cpsr
-	eor	r0, r0, #(\mode ^ SVC_MODE | PSR_ISETSTATE)
-	msr	spsr_cxsf, r0
-
-	@
-	@ the branch table must immediately follow this code
-	@
-	and	lr, lr, #0x0f
- THUMB(	adr	r0, 1f			)
- THUMB(	ldr	lr, [r0, lr, lsl #2]	)
-	mov	r0, sp
- ARM(	ldr	lr, [pc, lr, lsl #2]	)
-	movs	pc, lr			@ branch to handler in SVC mode
-ENDPROC(vector_\name)
-
-	.align	2
-	@ handler addresses follow this label
-1:
-	.endm
-
 	.globl	__stubs_start
 __stubs_start:
 /*
diff --git a/arch/arm/kernel/entry-header.S b/arch/arm/kernel/entry-header.S
index 9a8531e..c3c09ac 100644
--- a/arch/arm/kernel/entry-header.S
+++ b/arch/arm/kernel/entry-header.S
@@ -73,6 +73,109 @@
 	msr	cpsr_c, \rtemp			@ switch back to the SVC mode
 	.endm
 
+/*
+ * Vector stubs.
+ *
+ * This code is copied to 0xffff0200 so we can use branches in the
+ * vectors, rather than ldr's.  Note that this code must not
+ * exceed 0x300 bytes.
+ *
+ * Common stub entry macro:
+ *   Enter in IRQ mode, spsr = SVC/USR CPSR, lr = SVC/USR PC
+ *
+ * SP points to a minimal amount of processor-private memory, the address
+ * of which is copied into r0 for the mode specific abort handler.
+ */
+	.macro	vector_stub, name, mode, correction=0
+	.align	5
+
+vector_\name:
+	.if \correction
+	sub	lr, lr, #\correction
+	.endif
+
+	@
+	@ Save r0, lr_<exception> (parent PC) and spsr_<exception>
+	@ (parent CPSR)
+	@
+	stmia	sp, {r0, lr}		@ save r0, lr
+	mrs	lr, spsr
+	str	lr, [sp, #8]		@ save spsr
+
+	@
+	@ Prepare for SVC32 mode.  IRQs remain disabled.
+	@
+	mrs	r0, cpsr
+	eor	r0, r0, #(\mode ^ SVC_MODE | PSR_ISETSTATE)
+	msr	spsr_cxsf, r0
+
+	@
+	@ the branch table must immediately follow this code
+	@
+	and	lr, lr, #0x0f
+ THUMB(	adr	r0, 1f			)
+ THUMB(	ldr	lr, [r0, lr, lsl #2]	)
+	mov	r0, sp
+ ARM(	ldr	lr, [pc, lr, lsl #2]	)
+	movs	pc, lr			@ branch to handler in SVC mode
+ENDPROC(vector_\name)
+
+	.align	2
+	@ handler addresses follow this label
+1:
+	.endm
+
+/*
+ * SVC mode handlers
+ */
+
+#if defined(CONFIG_AEABI) && (__LINUX_ARM_ARCH__ >= 5)
+#define SPFIX(code...) code
+#else
+#define SPFIX(code...)
+#endif
+
+	.macro	svc_entry, stack_hole=0
+ UNWIND(.fnstart		)
+ UNWIND(.save {r0 - pc}		)
+	sub	sp, sp, #(S_FRAME_SIZE + \stack_hole - 4)
+#ifdef CONFIG_THUMB2_KERNEL
+ SPFIX(	str	r0, [sp]	)	@ temporarily saved
+ SPFIX(	mov	r0, sp		)
+ SPFIX(	tst	r0, #4		)	@ test original stack alignment
+ SPFIX(	ldr	r0, [sp]	)	@ restored
+#else
+ SPFIX(	tst	sp, #4		)
+#endif
+ SPFIX(	subeq	sp, sp, #4	)
+	stmia	sp, {r1 - r12}
+
+	ldmia	r0, {r3 - r5}
+	add	r7, sp, #S_SP - 4	@ here for interlock avoidance
+	mov	r6, #-1			@  ""  ""      ""       ""
+	add	r2, sp, #(S_FRAME_SIZE + \stack_hole - 4)
+ SPFIX(	addeq	r2, r2, #4	)
+	str	r3, [sp, #-4]!		@ save the "real" r0 copied
+					@ from the exception stack
+
+	mov	r3, lr
+
+	@
+	@ We are now ready to fill in the remaining blanks on the stack:
+	@
+	@  r2 - sp_svc
+	@  r3 - lr_svc
+	@  r4 - lr_<exception>, already fixed up for correct return/restart
+	@  r5 - spsr_<exception>
+	@  r6 - orig_r0 (see pt_regs definition in ptrace.h)
+	@
+	stmia	r7, {r2 - r6}
+
+#ifdef CONFIG_TRACE_IRQFLAGS
+	bl	trace_hardirqs_off
+#endif
+	.endm
+
 #ifndef CONFIG_THUMB2_KERNEL
 	.macro	svc_exit, rpsr
 	msr	spsr_cxsf, \rpsr
@@ -164,6 +267,73 @@
 #endif	/* !CONFIG_THUMB2_KERNEL */
 
 /*
+ * User mode handlers
+ *
+ * EABI note: sp_svc is always 64-bit aligned here, so should S_FRAME_SIZE
+ */
+
+#if defined(CONFIG_AEABI) && (__LINUX_ARM_ARCH__ >= 5) && (S_FRAME_SIZE & 7)
+#error "sizeof(struct pt_regs) must be a multiple of 8"
+#endif
+
+	.macro	usr_entry
+ UNWIND(.fnstart	)
+ UNWIND(.cantunwind	)	@ don't unwind the user space
+	sub	sp, sp, #S_FRAME_SIZE
+ ARM(	stmib	sp, {r1 - r12}	)
+ THUMB(	stmia	sp, {r0 - r12}	)
+
+	ldmia	r0, {r3 - r5}
+	add	r0, sp, #S_PC		@ here for interlock avoidance
+	mov	r6, #-1			@  ""  ""     ""        ""
+
+	str	r3, [sp]		@ save the "real" r0 copied
+					@ from the exception stack
+
+	@
+	@ We are now ready to fill in the remaining blanks on the stack:
+	@
+	@  r4 - lr_<exception>, already fixed up for correct return/restart
+	@  r5 - spsr_<exception>
+	@  r6 - orig_r0 (see pt_regs definition in ptrace.h)
+	@
+	@ Also, separately save sp_usr and lr_usr
+	@
+	stmia	r0, {r4 - r6}
+ ARM(	stmdb	r0, {sp, lr}^			)
+ THUMB(	store_user_sp_lr r0, r1, S_SP - S_PC	)
+
+	@
+	@ Enable the alignment trap while in kernel mode
+	@
+	alignment_trap r0
+
+	@
+	@ Clear FP to mark the first stack frame
+	@
+	zero_fp
+
+#ifdef CONFIG_IRQSOFF_TRACER
+	bl	trace_hardirqs_off
+#endif
+	.endm
+
+	.macro	kuser_cmpxchg_check
+#if !defined(CONFIG_CPU_32v6K) && !defined(CONFIG_NEEDS_SYSCALL_FOR_CMPXCHG)
+#ifndef CONFIG_MMU
+#warning "NPTL on non MMU needs fixing"
+#else
+	@ Make sure our user space atomic helper is restarted
+	@ if it was interrupted in a critical region.  Here we
+	@ perform a quick test inline since it should be false
+	@ 99.9999% of the time.  The rest is done out of line.
+	cmp	r4, #TASK_SIZE
+	blhs	kuser_cmpxchg64_fixup
+#endif
+#endif
+	.endm
+
+/*
  * These are the registers used in the syscall handler, and allow us to
  * have in theory up to 7 arguments to a function - r0 to r6.
  *
-- 
1.7.10.4

[PATCH 07/11] ARM: Add KGDB/KDB FIQ debugger generic code

[Anton Vorontsov]

The FIQ debugger may be used to debug situations when the kernel stuck
in uninterruptable sections, e.g. the kernel infinitely loops or
deadlocked in an interrupt or with interrupts disabled.

By default KGDB FIQ is disabled in runtime, but can be enabled with
kgdb_fiq.enable=1 kernel command line option.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 arch/arm/Kconfig                 |   18 +++++++
 arch/arm/include/asm/kgdb.h      |    8 +++
 arch/arm/kernel/Makefile         |    1 +
 arch/arm/kernel/kgdb_fiq.c       |  101 ++++++++++++++++++++++++++++++++++++++
 arch/arm/kernel/kgdb_fiq_entry.S |   79 +++++++++++++++++++++++++++++
 5 files changed, 207 insertions(+)
 create mode 100644 arch/arm/kernel/kgdb_fiq.c
 create mode 100644 arch/arm/kernel/kgdb_fiq_entry.S

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index a91009c..ae6ddf1 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -172,6 +172,24 @@ config GENERIC_ISA_DMA
 config FIQ
 	bool
 
+config ARCH_MIGHT_HAVE_FIQ
+	bool
+
+config KGDB_FIQ
+	bool "KGDB/KDB FIQ debugger"
+	depends on KGDB_KDB && ARCH_MIGHT_HAVE_FIQ && !THUMB2_KERNEL
+	select FIQ
+	help
+	  The FIQ debugger may be used to debug situations when the
+	  kernel stuck in uninterruptable sections, e.g. the kernel
+	  infinitely loops or deadlocked in an interrupt or with
+	  interrupts disabled.
+
+	  By default KGDB FIQ is disabled in runtime, but can be
+	  enabled with kgdb_fiq.enable=1 kernel command line option.
+
+	  If unsure, say N.
+
 config NEED_RET_TO_USER
 	bool
 
diff --git a/arch/arm/include/asm/kgdb.h b/arch/arm/include/asm/kgdb.h
index 48066ce..807e547 100644
--- a/arch/arm/include/asm/kgdb.h
+++ b/arch/arm/include/asm/kgdb.h
@@ -11,6 +11,8 @@
 #define __ARM_KGDB_H__
 
 #include <linux/ptrace.h>
+#include <linux/linkage.h>
+#include <asm/exception.h>
 
 /*
  * GDB assumes that we're a user process being debugged, so
@@ -47,6 +49,12 @@ static inline void arch_kgdb_breakpoint(void)
 extern void kgdb_handle_bus_error(void);
 extern int kgdb_fault_expected;
 
+extern char kgdb_fiq_handler;
+extern char kgdb_fiq_handler_end;
+asmlinkage void __exception_irq_entry kgdb_fiq_do_handle(struct pt_regs *regs);
+extern int __init kgdb_register_fiq(unsigned int mach_kgdb_fiq,
+		     void (*mach_kgdb_enable_fiq)(unsigned int irq, bool on),
+		     bool (*mach_is_kgdb_fiq)(unsigned int irq));
 #endif /* !__ASSEMBLY__ */
 
 /*
diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index 7ad2d5c..5aa079b 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -56,6 +56,7 @@ obj-$(CONFIG_ATAGS_PROC)	+= atags.o
 obj-$(CONFIG_OABI_COMPAT)	+= sys_oabi-compat.o
 obj-$(CONFIG_ARM_THUMBEE)	+= thumbee.o
 obj-$(CONFIG_KGDB)		+= kgdb.o
+obj-$(CONFIG_KGDB_FIQ)		+= kgdb_fiq_entry.o kgdb_fiq.o
 obj-$(CONFIG_ARM_UNWIND)	+= unwind.o
 obj-$(CONFIG_HAVE_TCM)		+= tcm.o
 obj-$(CONFIG_OF)		+= devtree.o
diff --git a/arch/arm/kernel/kgdb_fiq.c b/arch/arm/kernel/kgdb_fiq.c
new file mode 100644
index 0000000..72a62c7
--- /dev/null
+++ b/arch/arm/kernel/kgdb_fiq.c
@@ -0,0 +1,101 @@
+/*
+ * KGDB FIQ entry
+ *
+ * Copyright 2010 Google, Inc.
+ *		  Arve Hjønnevåg <arve@android.com>
+ *		  Colin Cross <ccross@android.com>
+ * Copyright 2012 Linaro Ltd.
+ *		  Anton Vorontsov <anton.vorontsov@linaro.org>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published
+ * by the Free Software Foundation.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/errno.h>
+#include <linux/hardirq.h>
+#include <linux/kgdb.h>
+#include <asm/fiq.h>
+#include <asm/exception.h>
+
+static int kgdb_fiq_enabled;
+module_param_named(enable, kgdb_fiq_enabled, int, 0600);
+MODULE_PARM_DESC(enable, "set to 1 to enable FIQ KGDB");
+
+static unsigned int kgdb_fiq;
+static void (*kgdb_enable_fiq)(unsigned int irq, bool on);
+static bool (*is_kgdb_fiq)(unsigned int irq);
+
+asmlinkage void __exception_irq_entry kgdb_fiq_do_handle(struct pt_regs *regs)
+{
+	if (!is_kgdb_fiq(kgdb_fiq))
+		return;
+	dbg_io_ops->clear_irqs();
+
+	nmi_enter();
+	kgdb_handle_exception(1, 0, 0, regs);
+	nmi_exit();
+}
+
+static struct fiq_handler kgdb_fiq_desc = {
+	.name = "kgdb",
+};
+
+static long kgdb_fiq_setup_stack(void *info)
+{
+	struct pt_regs regs;
+
+	regs.ARM_sp = __get_free_pages(GFP_KERNEL, THREAD_SIZE_ORDER) +
+			THREAD_START_SP;
+	WARN_ON(!regs.ARM_sp);
+
+	set_fiq_regs(&regs);
+	return 0;
+}
+
+int kgdb_arch_enable_nmi(bool on)
+{
+	static int cnt;
+
+	if (cnt > 0 && on)
+		return cnt;
+	cnt += on ? 1 : -1;
+	kgdb_enable_fiq(kgdb_fiq, cnt > 0);
+	return cnt;
+}
+
+int __init kgdb_register_fiq(unsigned int mach_kgdb_fiq,
+		void (*mach_kgdb_enable_fiq)(unsigned int irq, bool on),
+		bool (*mach_is_kgdb_fiq)(unsigned int irq))
+{
+	int err;
+	int cpu;
+
+	if (!kgdb_fiq_enabled)
+		return -ENODEV;
+	if (kgdb_fiq)
+		return -EBUSY;
+
+	kgdb_fiq = mach_kgdb_fiq;
+	kgdb_enable_fiq = mach_kgdb_enable_fiq;
+	is_kgdb_fiq = mach_is_kgdb_fiq;
+
+	err = claim_fiq(&kgdb_fiq_desc);
+	if (err) {
+		pr_warn("%s: unable to claim fiq", __func__);
+		return err;
+	}
+
+	for_each_possible_cpu(cpu)
+		work_on_cpu(cpu, kgdb_fiq_setup_stack, NULL);
+
+	set_fiq_handler(&kgdb_fiq_handler,
+			&kgdb_fiq_handler_end - &kgdb_fiq_handler);
+
+	kgdb_arch_enable_nmi(1);
+	return 0;
+}
diff --git a/arch/arm/kernel/kgdb_fiq_entry.S b/arch/arm/kernel/kgdb_fiq_entry.S
new file mode 100644
index 0000000..7be3726
--- /dev/null
+++ b/arch/arm/kernel/kgdb_fiq_entry.S
@@ -0,0 +1,79 @@
+/*
+ * KGDB FIQ entry
+ *
+ * Copyright 1996,1997,1998 Russell King.
+ * Copyright 2012 Linaro Ltd.
+ *		  Anton Vorontsov <anton.vorontsov@linaro.org>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published
+ * by the Free Software Foundation.
+ */
+
+#include <linux/linkage.h>
+#include <asm/assembler.h>
+#include <asm/memory.h>
+#include <asm/unwind.h>
+#include "entry-header.S"
+
+	.text
+
+@ This is needed for usr_entry/alignment_trap
+.LCcralign:
+	.long	cr_alignment
+.LCdohandle:
+	.long	kgdb_fiq_do_handle
+
+	.macro	fiq_handler
+	ldr	r1, =.LCdohandle
+	mov	r0, sp
+	adr	lr, BSYM(9997f)
+	ldr	pc, [r1]
+9997:
+	.endm
+
+	.align	5
+__fiq_svc:
+	svc_entry
+	fiq_handler
+	svc_exit r5				@ return from exception
+ UNWIND(.fnend		)
+ENDPROC(__fiq_svc)
+	.ltorg
+
+	.align	5
+__fiq_usr:
+	usr_entry
+	kuser_cmpxchg_check
+	fiq_handler
+	get_thread_info tsk
+	mov	why, #0
+	b	ret_to_user_from_irq
+ UNWIND(.fnend		)
+ENDPROC(__fiq_usr)
+	.ltorg
+
+	.global kgdb_fiq_handler
+kgdb_fiq_handler:
+
+	vector_stub	fiq, FIQ_MODE, 4
+
+	.long	__fiq_usr			@  0  (USR_26 / USR_32)
+	.long	__fiq_svc			@  1  (FIQ_26 / FIQ_32)
+	.long	__fiq_svc			@  2  (IRQ_26 / IRQ_32)
+	.long	__fiq_svc			@  3  (SVC_26 / SVC_32)
+	.long	__fiq_svc			@  4
+	.long	__fiq_svc			@  5
+	.long	__fiq_svc			@  6
+	.long	__fiq_svc			@  7
+	.long	__fiq_svc			@  8
+	.long	__fiq_svc			@  9
+	.long	__fiq_svc			@  a
+	.long	__fiq_svc			@  b
+	.long	__fiq_svc			@  c
+	.long	__fiq_svc			@  d
+	.long	__fiq_svc			@  e
+	.long	__fiq_svc			@  f
+
+	.global kgdb_fiq_handler_end
+kgdb_fiq_handler_end:
-- 
1.7.10.4

[PATCH 08/11] ARM: kgdb_fiq: Implement knocking into KDB via escape command

[Anton Vorontsov]

As Colin Cross noticed, serial ports could be noisy, so occasional
characters once in a while are possible. So, considering the noise
possibility, entering the debugger on any received byte is unacceptable
for production devices.

This changes KGDB FIQ behaviour in a such way so that we have to type the
GDB-protocol "$3#33" command to actually enter the debugger, the kernel
will print the following prompt:

	Type $3#33 to enter the debugger>

This is the exactly the same command we use to escape from KGDB to KDB,
so it should be all pretty familiar.

For convenience, there is a kgdb_fiq.knock kernel command line option,
when set to 0, this turns the special command to just a return key
press, so the kernel will be printing this:

	Hit <return> to enter the debugger>

And for the cases when NMI connected to a dedicated button, the knocking
can be disabled altogether by setting kgdb_fiq.knock to -1.

Suggested-by: Colin Cross <ccross@android.com>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 arch/arm/kernel/kgdb_fiq.c |   58 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 58 insertions(+)

diff --git a/arch/arm/kernel/kgdb_fiq.c b/arch/arm/kernel/kgdb_fiq.c
index 72a62c7..2bf4467 100644
--- a/arch/arm/kernel/kgdb_fiq.c
+++ b/arch/arm/kernel/kgdb_fiq.c
@@ -18,6 +18,7 @@
 #include <linux/slab.h>
 #include <linux/errno.h>
 #include <linux/hardirq.h>
+#include <linux/kdb.h>
 #include <linux/kgdb.h>
 #include <asm/fiq.h>
 #include <asm/exception.h>
@@ -26,6 +27,60 @@ static int kgdb_fiq_enabled;
 module_param_named(enable, kgdb_fiq_enabled, int, 0600);
 MODULE_PARM_DESC(enable, "set to 1 to enable FIQ KGDB");
 
+static int kgdb_fiq_knock = 1;
+module_param_named(knock, kgdb_fiq_knock, int, 0600);
+MODULE_PARM_DESC(knock, "if set to 1 (default), the special '$3#33' command "
+			"must be used to enter the debugger; when set to 0, "
+			"hitting return key is enough to enter the debugger; "
+			"when set to -1, the debugger is entered immediately "
+			"upon NMI");
+
+/*
+ * "Serial ports are often noisy, especially when muxed over another port (we
+ * often use serial over the headset connector). Noise on the async command
+ * line just causes characters that are ignored, on a command line that blocked
+ * execution noise would be catastrophic." -- Colin Cross
+ *
+ * So, this small function implements KGDB/KDB knocking on the serial line: we
+ * won't enter the debugger until we receive a known magic phrase (which is
+ * actually "$3#33", known as "escape to KDB" command. If knocking is disabled,
+ * just pressing the return key is enough to enter the debugger.
+ */
+static bool kgdb_fiq_poll_knock(void)
+{
+	static int n;
+	int c = -1;
+	get_char_func *getc;
+	char magic[] = "$3#33";
+	size_t m = strlen(magic);
+
+	if (kgdb_fiq_knock < 0)
+		return 1;
+
+	for (getc = &kdb_poll_funcs[0]; *getc; ++getc) {
+		c = (*getc)();
+		if (c >= 0)
+			break;
+	}
+
+	if (!kgdb_fiq_knock && (c == '\r' || c == '\n')) {
+		return 1;
+	} else if (c == magic[n]) {
+		kdb_printf("%c", c);
+		n = (n + 1) % m;
+		if (!n)
+			return 1;
+	} else {
+		n = 0;
+		kdb_printf("\r%s %s to enter the debugger> %*s",
+			   kgdb_fiq_knock ? "Type" : "Hit",
+			   kgdb_fiq_knock ? magic  : "<return>", m, "");
+		memset(magic, '\b', m);
+		kdb_printf("%s", magic);
+	}
+	return 0;
+}
+
 static unsigned int kgdb_fiq;
 static void (*kgdb_enable_fiq)(unsigned int irq, bool on);
 static bool (*is_kgdb_fiq)(unsigned int irq);
@@ -36,6 +91,9 @@ asmlinkage void __exception_irq_entry kgdb_fiq_do_handle(struct pt_regs *regs)
 		return;
 	dbg_io_ops->clear_irqs();
 
+	if (!kgdb_fiq_poll_knock())
+		return;
+
 	nmi_enter();
 	kgdb_handle_exception(1, 0, 0, regs);
 	nmi_exit();
-- 
1.7.10.4

[PATCH 09/11] ARM: VIC: Add a couple of low-level FIQ management helpers

[Anton Vorontsov]

Just a couple of calls to manage VIC FIQ routing. We'll use them for
KGDB FIQ support on ARM Versatile machines.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 arch/arm/common/vic.c               |   28 ++++++++++++++++++++++++++++
 arch/arm/include/asm/hardware/vic.h |    2 ++
 2 files changed, 30 insertions(+)

diff --git a/arch/arm/common/vic.c b/arch/arm/common/vic.c
index e0d5388..df2fc82 100644
--- a/arch/arm/common/vic.c
+++ b/arch/arm/common/vic.c
@@ -66,6 +66,34 @@ static struct vic_device vic_devices[CONFIG_ARM_VIC_NR];
 
 static int vic_id;
 
+static void __iomem *vic_base(struct irq_data *d)
+{
+	return (void __iomem *)irq_data_get_irq_chip_data(d);
+}
+
+void vic_fiq_select(unsigned int irq, bool on)
+{
+	void __iomem *base = vic_base(&irq_to_desc(irq)->irq_data);
+	void __iomem *sel = base + VIC_INT_SELECT;
+	u32 msk = 1 << irq;
+	u32 val;
+
+	pr_debug("rerouting VIC vector %d to %s\n", irq, on ? "FIQ" : "IRQ");
+
+	val = readl(sel);
+	val &= ~msk;
+	if (on)
+		val |= msk;
+	writel(val, sel);
+}
+
+bool vic_is_fiq_rised(unsigned int irq)
+{
+	void __iomem *base = vic_base(&irq_to_desc(irq)->irq_data);
+
+	return readl(base + VIC_FIQ_STATUS) & (1 << irq);
+}
+
 /**
  * vic_init2 - common initialisation code
  * @base: Base of the VIC.
diff --git a/arch/arm/include/asm/hardware/vic.h b/arch/arm/include/asm/hardware/vic.h
index e14af1a..2728975 100644
--- a/arch/arm/include/asm/hardware/vic.h
+++ b/arch/arm/include/asm/hardware/vic.h
@@ -52,6 +52,8 @@ void __vic_init(void __iomem *base, unsigned int irq_start, u32 vic_sources,
 void vic_init(void __iomem *base, unsigned int irq_start, u32 vic_sources, u32 resume_sources);
 int vic_of_init(struct device_node *node, struct device_node *parent);
 void vic_handle_irq(struct pt_regs *regs);
+void vic_fiq_select(unsigned int irq, bool on);
+bool vic_is_fiq_rised(unsigned int irq);
 
 #endif /* __ASSEMBLY__ */
 #endif
-- 
1.7.10.4

[PATCH 10/11] ARM: versatile: Make able to use UART ports for KGDB FIQ debugger

[Anton Vorontsov]

If enabled, kernel will able to enter KGDB upon serial line activity on
UART ports.

Note that even with this patch and CONFIG_KGDB_FIQ is enabled, you still
need to pass kgdb_fiq.enable=1 kernel command line option, otherwise UART
will behave in a normal way.

By default UART0 is used, but this can be changed via kgdb_fiq.uart_num
kernel command line option.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 arch/arm/Kconfig                            |    1 +
 arch/arm/mach-versatile/Makefile            |    1 +
 arch/arm/mach-versatile/include/mach/irqs.h |    1 +
 arch/arm/mach-versatile/kgdb_fiq.c          |   31 +++++++++++++++++++++++++++
 4 files changed, 34 insertions(+)
 create mode 100644 arch/arm/mach-versatile/kgdb_fiq.c

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index ae6ddf1..c0df1ba 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -311,6 +311,7 @@ config ARCH_VERSATILE
 	select ICST
 	select GENERIC_CLOCKEVENTS
 	select ARCH_WANT_OPTIONAL_GPIOLIB
+	select ARCH_MIGHT_HAVE_FIQ
 	select NEED_MACH_IO_H if PCI
 	select PLAT_VERSATILE
 	select PLAT_VERSATILE_CLCD
diff --git a/arch/arm/mach-versatile/Makefile b/arch/arm/mach-versatile/Makefile
index 81fa3fe..bfd761f 100644
--- a/arch/arm/mach-versatile/Makefile
+++ b/arch/arm/mach-versatile/Makefile
@@ -7,3 +7,4 @@ obj-$(CONFIG_ARCH_VERSATILE_PB)		+= versatile_pb.o
 obj-$(CONFIG_MACH_VERSATILE_AB)		+= versatile_ab.o
 obj-$(CONFIG_MACH_VERSATILE_DT)		+= versatile_dt.o
 obj-$(CONFIG_PCI)			+= pci.o
+obj-$(CONFIG_KGDB_FIQ)			+= kgdb_fiq.o
diff --git a/arch/arm/mach-versatile/include/mach/irqs.h b/arch/arm/mach-versatile/include/mach/irqs.h
index bf44c61..fcd2a95 100644
--- a/arch/arm/mach-versatile/include/mach/irqs.h
+++ b/arch/arm/mach-versatile/include/mach/irqs.h
@@ -26,6 +26,7 @@
  *  held within platform.h
  */
 #define IRQ_VIC_START		0
+#define FIQ_START		IRQ_VIC_START
 #define IRQ_WDOGINT		(IRQ_VIC_START + INT_WDOGINT)
 #define IRQ_SOFTINT		(IRQ_VIC_START + INT_SOFTINT)
 #define IRQ_COMMRx		(IRQ_VIC_START + INT_COMMRx)
diff --git a/arch/arm/mach-versatile/kgdb_fiq.c b/arch/arm/mach-versatile/kgdb_fiq.c
new file mode 100644
index 0000000..3cdf71d
--- /dev/null
+++ b/arch/arm/mach-versatile/kgdb_fiq.c
@@ -0,0 +1,31 @@
+/*
+ * KGDB FIQ board support
+ *
+ * Copyright 2012 Linaro Ltd.
+ *		  Anton Vorontsov <anton.vorontsov@linaro.org>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published
+ * by the Free Software Foundation.
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/kgdb.h>
+#include <mach/hardware.h>
+#include <mach/platform.h>
+#include <asm/hardware/vic.h>
+
+static int kgdb_fiq;
+module_param_named(uart_num, kgdb_fiq, int, 0600);
+MODULE_PARM_DESC(uart_num, "UART<number> port to use for KGDB FIQ");
+
+static int __init kgdb_fiq_init(void)
+{
+	WARN_ON(kgdb_fiq > INT_UARTINT2 - INT_UARTINT0);
+
+	return kgdb_register_fiq(INT_UARTINT0 + kgdb_fiq,
+				 vic_fiq_select,
+				 vic_is_fiq_rised);
+}
+console_initcall(kgdb_fiq_init);
-- 
1.7.10.4

[PATCH 11/11] ARM: Get rid of .LCcralign local label usage in alignment_trap macro

[Anton Vorontsov]

This makes the code more izolated.

The downside of this is that we now have an additional branch and the
code itself is 8 bytes longer. But on the bright side, this new layout
can be more cache friendly since cr_alignment address might be already
in the cache line (not that I measured anything, it's just fun to think
about it).

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 arch/arm/kernel/entry-armv.S     |    2 --
 arch/arm/kernel/entry-header.S   |    6 +++++-
 arch/arm/kernel/kgdb_fiq_entry.S |    3 ---
 3 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 6aeb9b8..6b04ab5 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -266,8 +266,6 @@ __pabt_svc:
 ENDPROC(__pabt_svc)
 
 	.align	5
-.LCcralign:
-	.word	cr_alignment
 #ifdef MULTI_DABORT
 .LCprocfns:
 	.word	processor
diff --git a/arch/arm/kernel/entry-header.S b/arch/arm/kernel/entry-header.S
index c3c09ac..5a05e7f 100644
--- a/arch/arm/kernel/entry-header.S
+++ b/arch/arm/kernel/entry-header.S
@@ -38,9 +38,13 @@
 
 	.macro	alignment_trap, rtemp
 #ifdef CONFIG_ALIGNMENT_TRAP
-	ldr	\rtemp, .LCcralign
+	ldr	\rtemp, 1f
 	ldr	\rtemp, [\rtemp]
 	mcr	p15, 0, \rtemp, c1, c0
+	b	2f
+1:
+	.word	cr_alignment
+2:
 #endif
 	.endm
 
diff --git a/arch/arm/kernel/kgdb_fiq_entry.S b/arch/arm/kernel/kgdb_fiq_entry.S
index 7be3726..e7c05fc 100644
--- a/arch/arm/kernel/kgdb_fiq_entry.S
+++ b/arch/arm/kernel/kgdb_fiq_entry.S
@@ -18,9 +18,6 @@
 
 	.text
 
-@ This is needed for usr_entry/alignment_trap
-.LCcralign:
-	.long	cr_alignment
 .LCdohandle:
 	.long	kgdb_fiq_do_handle
 
-- 
1.7.10.4

Re: [PATCH 07/11] ARM: Add KGDB/KDB FIQ debugger generic code

[Russell King - ARM Linux]

On Mon, Jul 30, 2012 at 04:58:16AM -0700, Anton Vorontsov wrote:
> +	.align	5
> +__fiq_svc:
> +	svc_entry
> +	fiq_handler
> +	svc_exit r5				@ return from exception
> + UNWIND(.fnend		)
> +ENDPROC(__fiq_svc)
> +	.ltorg
> +
> +	.align	5
> +__fiq_usr:
> +	usr_entry
> +	kuser_cmpxchg_check
> +	fiq_handler
> +	get_thread_info tsk
> +	mov	why, #0
> +	b	ret_to_user_from_irq
> + UNWIND(.fnend		)
> +ENDPROC(__fiq_usr)
> +	.ltorg
> +
> +	.global kgdb_fiq_handler
> +kgdb_fiq_handler:
> +
> +	vector_stub	fiq, FIQ_MODE, 4
> +
> +	.long	__fiq_usr			@  0  (USR_26 / USR_32)
> +	.long	__fiq_svc			@  1  (FIQ_26 / FIQ_32)
> +	.long	__fiq_svc			@  2  (IRQ_26 / IRQ_32)
> +	.long	__fiq_svc			@  3  (SVC_26 / SVC_32)
> +	.long	__fiq_svc			@  4
> +	.long	__fiq_svc			@  5
> +	.long	__fiq_svc			@  6
> +	.long	__fiq_svc			@  7
> +	.long	__fiq_svc			@  8
> +	.long	__fiq_svc			@  9
> +	.long	__fiq_svc			@  a
> +	.long	__fiq_svc			@  b
> +	.long	__fiq_svc			@  c
> +	.long	__fiq_svc			@  d
> +	.long	__fiq_svc			@  e
> +	.long	__fiq_svc			@  f

I am not convinced that this does not cause loss of state from the parent
context.  Let's review what happens when a FIQ is received from SVC mode
with the above code.

- The CPU will be in SVC mode.
- FIQ received.
- CPU saves CPSR into SPSR_fiq and PC into LR_fiq, and jumps to the FIQ
  vector.
- We apply the 4 byte correction to LR_fiq, and store r0, LR_fiq and
  SPSR_fiq to the FIQ 'stack'
- We switch to SVC mode and jump to __fiq_svc
- svc_entry:
  - adjusts the SVC stack pointer down, and saves r1 - r12
  - loads r0, LR_fiq and SPSR_fiq and saves them as ARM_r0, ARM_pc, ARM_cpsr
    into the pt_regs
  - the original value of the SVC stack pointer is saved as ARM_r13
  - LR_svc is saved as ARM_r14

At this point, we have saved everything *except* for the SPSR_svc register.

Now, when we return from the above, we use svc_exit:
- write SPSR_svc with ARM_cpsr (from SPSR_fiq)
- load r0-pc from the pt_regs and load CPSR from SPSR_svc

Now the thing here is that even if we did preserve SPSR_svc, with the
above exit sequence, there is _no_ way to preserve the value of SPSR_svc.
Normally, this doesn't matter because we know that the regions we care
about this have IRQs disabled.

However, what this means, if we receive an FIQ and use this path from any
part of the kernel which expects SPSR_svc to be preserved (eg, the exit
path from any exception) the kernel will blow up.

I guess you could do something like this instead:
- disable FIQs
- load SPSR_svc with a saved value of it from entry.
- load r1-r14 from ARM_r1..ARM_lr
- switch to FIQ mode
- load SPSR_fiq from saved ARM_cpsr
- load r0 from ARM_r0
- load pc from ARM_pc

So, maybe something like this for the svc return path:

	cpsid	f
	ldr	r1, [saved_spsr_svc]
	mov	r0, sp
	mrs	spsr_cxsf, r1
	ldmib	r0, {r1 - r14}
	msr	cpsr_c, #FIQ_MODE | PSR_I_BIT | PSR_F_BIT
	add	r7, r0, #S_PC
	ldr	r8, [r0, #S_CPSR]
	mrs	spsr_cxsf, r8
	ldr	r0, [r0, #S_R0]
	ldmia	r7, {pc}^

Re: [PATCH 11/11] ARM: Get rid of .LCcralign local label usage in alignment_trap macro

[Russell King - ARM Linux]

On Mon, Jul 30, 2012 at 04:58:20AM -0700, Anton Vorontsov wrote:
> This makes the code more izolated.
> 
> The downside of this is that we now have an additional branch and the
> code itself is 8 bytes longer. But on the bright side, this new layout
> can be more cache friendly since cr_alignment address might be already
> in the cache line (not that I measured anything, it's just fun to think
> about it).

The caches are harvard, so mixing data and code together does not increase
performance.  Having data which is used by the same code in the same cache
line results in better performance.

The additional branch will also cause a pipeline stall on older CPUs.

So no, I don't see any way that this is a performance improvement.  Please
leave this as is.

Re: [PATCH 10/11] ARM: versatile: Make able to use UART ports for KGDB FIQ debugger

[Russell King - ARM Linux]

On Mon, Jul 30, 2012 at 04:58:19AM -0700, Anton Vorontsov wrote:
> diff --git a/arch/arm/mach-versatile/include/mach/irqs.h b/arch/arm/mach-versatile/include/mach/irqs.h
> index bf44c61..fcd2a95 100644
> --- a/arch/arm/mach-versatile/include/mach/irqs.h
> +++ b/arch/arm/mach-versatile/include/mach/irqs.h
> @@ -26,6 +26,7 @@
>   *  held within platform.h
>   */
>  #define IRQ_VIC_START		0
> +#define FIQ_START		IRQ_VIC_START

No.  We want to ultimately get rid of FIQ_START.

Re: [PATCH 03/11] kdb: Implement disable_nmi command

[Colin Cross]

On Mon, Jul 30, 2012 at 4:58 AM, Anton Vorontsov
<anton.vorontsov@linaro.org> wrote:
> This command disables NMI-entry. If NMI source was previously shared with
> a serial console ("debug port"), this effectively releases the port from
> KDB exclusive use, and makes the console available for normal use.
>
> Of course, NMI can be reenabled, enable_nmi modparam is used for that:
>
>         echo 1 > /sys/module/kdb/parameters/enable_nmi

This is very different behavior from the FIQ debugger "console"
command you are trying to replace.  In the FIQ debugger, everything
goes through the FIQ/NMI, even when in console mode.  That means that
the user can always get back to FIQ debugger/KDB mode using a special
sequence (we use a break character).  With your implementation, if you
switch from KDB to console to see if the console is working, and find
that it is not working, you can never get back into KDB.

Re: [PATCH 01/11] kernel/debug: Make use of KGDB_REASON_NMI

[Jason Wessel]

On 07/30/2012 06:58 AM, Anton Vorontsov wrote:
> Currently kernel never set KGDB_REASON_NMI. We do now, when we enter
> KGDB/KDB from an NMI.
>
> This is not to be confused with kgdb_nmicallback(), NMI callback is
> an entry for the slave CPUs during CPUs roundup, but REASON_NMI is the
> entry for the master CPU.

No need for confusion here :-)

I'll take this one for the kernel merge window if it passes regression tests, no reason not to be setting the stop codes properly.

Thanks,
Jason.

Re: [PATCH 07/11] ARM: Add KGDB/KDB FIQ debugger generic code

[Anton Vorontsov]

On Mon, Jul 30, 2012 at 03:07:24PM +0100, Russell King - ARM Linux wrote:
[....]
> Now the thing here is that even if we did preserve SPSR_svc, with the
> above exit sequence, there is _no_ way to preserve the value of SPSR_svc.
> Normally, this doesn't matter because we know that the regions we care
> about this have IRQs disabled.

Wow, that is quite subtle. Indeed, now I clearly see that we do mangle
SVC's SPSR.

Thanks!

[...]
> So, maybe something like this for the svc return path:
> 
> 	cpsid	f
> 	ldr	r1, [saved_spsr_svc]
> 	mov	r0, sp
> 	mrs	spsr_cxsf, r1
> 	ldmib	r0, {r1 - r14}
> 	msr	cpsr_c, #FIQ_MODE | PSR_I_BIT | PSR_F_BIT
...
>       ldmia   r7, {pc}^

Yup, I got the idea: we have to restore the SPSR in SVC mode, but
then we switch to FIQ mode and exit the exception while being in
the FIQ mode, that way CPU won't change our restored SPSR_svc.

As for "saved_spsr_svc", I think the easiest way to get it, is to
switch to FIQ mode temporary, and read it from the stack.

(Plus, cpsid is not available for older CPUs, but the thing is that
we don't touch global enable/disable FIQs/IRQs flags, so I guess
I don't actually need it.)

So, that's what I've applied on top:

@@ -33,7 +33,20 @@
 __fiq_svc:
 	svc_entry
 	fiq_handler
-	svc_exit r5				@ return from exception
+	mrs	r4, cpsr
+	msr	cpsr_c, #FIQ_MODE | PSR_I_BIT | PSR_F_BIT
+	ldr	r1, [sp, #8]
+	msr	cpsr_c, r4
+	msr	spsr_cxsf, r1
+	mov	r0, sp
+	ldmib	r0, {r1 - r14}
+	msr	cpsr_c, #FIQ_MODE | PSR_I_BIT | PSR_F_BIT
+	add	r8, r0, #S_PC
+	ldr	r9, [r0, #S_PSR]
+	msr	spsr_cxsf, r9
+	ldr	r0, [r0, #S_R0]
+	ldmia	r8, {pc}^


And the whole fixed up patch is down below:

- - - -
From: Anton Vorontsov <anton.vorontsov@linaro.org>
Subject: ARM: Add KGDB/KDB FIQ debugger generic code

The FIQ debugger may be used to debug situations when the kernel stuck
in uninterruptable sections, e.g. the kernel infinitely loops or
deadlocked in an interrupt or with interrupts disabled.

By default KGDB FIQ is disabled in runtime, but can be enabled with
kgdb_fiq.enable=1 kernel command line option.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 arch/arm/Kconfig                 |   18 +++++++
 arch/arm/include/asm/kgdb.h      |    8 +++
 arch/arm/kernel/Makefile         |    1 +
 arch/arm/kernel/kgdb_fiq.c       |  101 ++++++++++++++++++++++++++++++++++++++
 arch/arm/kernel/kgdb_fiq_entry.S |   92 ++++++++++++++++++++++++++++++++++
 5 files changed, 220 insertions(+)
 create mode 100644 arch/arm/kernel/kgdb_fiq.c
 create mode 100644 arch/arm/kernel/kgdb_fiq_entry.S

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index a91009c..ae6ddf1 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -172,6 +172,24 @@ config GENERIC_ISA_DMA
 config FIQ
 	bool
 
+config ARCH_MIGHT_HAVE_FIQ
+	bool
+
+config KGDB_FIQ
+	bool "KGDB/KDB FIQ debugger"
+	depends on KGDB_KDB && ARCH_MIGHT_HAVE_FIQ && !THUMB2_KERNEL
+	select FIQ
+	help
+	  The FIQ debugger may be used to debug situations when the
+	  kernel stuck in uninterruptable sections, e.g. the kernel
+	  infinitely loops or deadlocked in an interrupt or with
+	  interrupts disabled.
+
+	  By default KGDB FIQ is disabled in runtime, but can be
+	  enabled with kgdb_fiq.enable=1 kernel command line option.
+
+	  If unsure, say N.
+
 config NEED_RET_TO_USER
 	bool
 
diff --git a/arch/arm/include/asm/kgdb.h b/arch/arm/include/asm/kgdb.h
index 48066ce..807e547 100644
--- a/arch/arm/include/asm/kgdb.h
+++ b/arch/arm/include/asm/kgdb.h
@@ -11,6 +11,8 @@
 #define __ARM_KGDB_H__
 
 #include <linux/ptrace.h>
+#include <linux/linkage.h>
+#include <asm/exception.h>
 
 /*
  * GDB assumes that we're a user process being debugged, so
@@ -47,6 +49,12 @@ static inline void arch_kgdb_breakpoint(void)
 extern void kgdb_handle_bus_error(void);
 extern int kgdb_fault_expected;
 
+extern char kgdb_fiq_handler;
+extern char kgdb_fiq_handler_end;
+asmlinkage void __exception_irq_entry kgdb_fiq_do_handle(struct pt_regs *regs);
+extern int __init kgdb_register_fiq(unsigned int mach_kgdb_fiq,
+		     void (*mach_kgdb_enable_fiq)(unsigned int irq, bool on),
+		     bool (*mach_is_kgdb_fiq)(unsigned int irq));
 #endif /* !__ASSEMBLY__ */
 
 /*
diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index 7ad2d5c..5aa079b 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -56,6 +56,7 @@ obj-$(CONFIG_ATAGS_PROC)	+= atags.o
 obj-$(CONFIG_OABI_COMPAT)	+= sys_oabi-compat.o
 obj-$(CONFIG_ARM_THUMBEE)	+= thumbee.o
 obj-$(CONFIG_KGDB)		+= kgdb.o
+obj-$(CONFIG_KGDB_FIQ)		+= kgdb_fiq_entry.o kgdb_fiq.o
 obj-$(CONFIG_ARM_UNWIND)	+= unwind.o
 obj-$(CONFIG_HAVE_TCM)		+= tcm.o
 obj-$(CONFIG_OF)		+= devtree.o
diff --git a/arch/arm/kernel/kgdb_fiq.c b/arch/arm/kernel/kgdb_fiq.c
new file mode 100644
index 0000000..72a62c7
--- /dev/null
+++ b/arch/arm/kernel/kgdb_fiq.c
@@ -0,0 +1,101 @@
+/*
+ * KGDB FIQ entry
+ *
+ * Copyright 2010 Google, Inc.
+ *		  Arve Hjønnevåg <arve@android.com>
+ *		  Colin Cross <ccross@android.com>
+ * Copyright 2012 Linaro Ltd.
+ *		  Anton Vorontsov <anton.vorontsov@linaro.org>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published
+ * by the Free Software Foundation.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/errno.h>
+#include <linux/hardirq.h>
+#include <linux/kgdb.h>
+#include <asm/fiq.h>
+#include <asm/exception.h>
+
+static int kgdb_fiq_enabled;
+module_param_named(enable, kgdb_fiq_enabled, int, 0600);
+MODULE_PARM_DESC(enable, "set to 1 to enable FIQ KGDB");
+
+static unsigned int kgdb_fiq;
+static void (*kgdb_enable_fiq)(unsigned int irq, bool on);
+static bool (*is_kgdb_fiq)(unsigned int irq);
+
+asmlinkage void __exception_irq_entry kgdb_fiq_do_handle(struct pt_regs *regs)
+{
+	if (!is_kgdb_fiq(kgdb_fiq))
+		return;
+	dbg_io_ops->clear_irqs();
+
+	nmi_enter();
+	kgdb_handle_exception(1, 0, 0, regs);
+	nmi_exit();
+}
+
+static struct fiq_handler kgdb_fiq_desc = {
+	.name = "kgdb",
+};
+
+static long kgdb_fiq_setup_stack(void *info)
+{
+	struct pt_regs regs;
+
+	regs.ARM_sp = __get_free_pages(GFP_KERNEL, THREAD_SIZE_ORDER) +
+			THREAD_START_SP;
+	WARN_ON(!regs.ARM_sp);
+
+	set_fiq_regs(&regs);
+	return 0;
+}
+
+int kgdb_arch_enable_nmi(bool on)
+{
+	static int cnt;
+
+	if (cnt > 0 && on)
+		return cnt;
+	cnt += on ? 1 : -1;
+	kgdb_enable_fiq(kgdb_fiq, cnt > 0);
+	return cnt;
+}
+
+int __init kgdb_register_fiq(unsigned int mach_kgdb_fiq,
+		void (*mach_kgdb_enable_fiq)(unsigned int irq, bool on),
+		bool (*mach_is_kgdb_fiq)(unsigned int irq))
+{
+	int err;
+	int cpu;
+
+	if (!kgdb_fiq_enabled)
+		return -ENODEV;
+	if (kgdb_fiq)
+		return -EBUSY;
+
+	kgdb_fiq = mach_kgdb_fiq;
+	kgdb_enable_fiq = mach_kgdb_enable_fiq;
+	is_kgdb_fiq = mach_is_kgdb_fiq;
+
+	err = claim_fiq(&kgdb_fiq_desc);
+	if (err) {
+		pr_warn("%s: unable to claim fiq", __func__);
+		return err;
+	}
+
+	for_each_possible_cpu(cpu)
+		work_on_cpu(cpu, kgdb_fiq_setup_stack, NULL);
+
+	set_fiq_handler(&kgdb_fiq_handler,
+			&kgdb_fiq_handler_end - &kgdb_fiq_handler);
+
+	kgdb_arch_enable_nmi(1);
+	return 0;
+}
diff --git a/arch/arm/kernel/kgdb_fiq_entry.S b/arch/arm/kernel/kgdb_fiq_entry.S
new file mode 100644
index 0000000..a6a1ad1
--- /dev/null
+++ b/arch/arm/kernel/kgdb_fiq_entry.S
@@ -0,0 +1,92 @@
+/*
+ * KGDB FIQ entry
+ *
+ * Copyright 1996,1997,1998 Russell King.
+ * Copyright 2012 Linaro Ltd.
+ *		  Anton Vorontsov <anton.vorontsov@linaro.org>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published
+ * by the Free Software Foundation.
+ */
+
+#include <linux/linkage.h>
+#include <asm/assembler.h>
+#include <asm/memory.h>
+#include <asm/unwind.h>
+#include "entry-header.S"
+
+	.text
+
+@ This is needed for usr_entry/alignment_trap
+.LCcralign:
+	.long	cr_alignment
+.LCdohandle:
+	.long	kgdb_fiq_do_handle
+
+	.macro	fiq_handler
+	ldr	r1, =.LCdohandle
+	mov	r0, sp
+	adr	lr, BSYM(9997f)
+	ldr	pc, [r1]
+9997:
+	.endm
+
+	.align	5
+__fiq_svc:
+	svc_entry
+	fiq_handler
+	mrs	r4, cpsr
+	msr	cpsr_c, #FIQ_MODE | PSR_I_BIT | PSR_F_BIT
+	ldr	r1, [sp, #8]
+	msr	cpsr_c, r4
+	msr	spsr_cxsf, r1
+	mov	r0, sp
+	ldmib	r0, {r1 - r14}
+	msr	cpsr_c, #FIQ_MODE | PSR_I_BIT | PSR_F_BIT
+	add	r8, r0, #S_PC
+	ldr	r9, [r0, #S_PSR]
+	msr	spsr_cxsf, r9
+	ldr	r0, [r0, #S_R0]
+	ldmia	r8, {pc}^
+
+ UNWIND(.fnend		)
+ENDPROC(__fiq_svc)
+	.ltorg
+
+	.align	5
+__fiq_usr:
+	usr_entry
+	kuser_cmpxchg_check
+	fiq_handler
+	get_thread_info tsk
+	mov	why, #0
+	b	ret_to_user_from_irq
+ UNWIND(.fnend		)
+ENDPROC(__fiq_usr)
+	.ltorg
+
+	.global kgdb_fiq_handler
+kgdb_fiq_handler:
+
+	vector_stub	fiq, FIQ_MODE, 4
+
+	.long	__fiq_usr			@  0  (USR_26 / USR_32)
+	.long	__fiq_svc			@  1  (FIQ_26 / FIQ_32)
+	.long	__fiq_svc			@  2  (IRQ_26 / IRQ_32)
+	.long	__fiq_svc			@  3  (SVC_26 / SVC_32)
+	.long	__fiq_svc			@  4
+	.long	__fiq_svc			@  5
+	.long	__fiq_svc			@  6
+	.long	__fiq_svc			@  7
+	.long	__fiq_svc			@  8
+	.long	__fiq_svc			@  9
+	.long	__fiq_svc			@  a
+	.long	__fiq_svc			@  b
+	.long	__fiq_svc			@  c
+	.long	__fiq_svc			@  d
+	.long	__fiq_svc			@  e
+	.long	__fiq_svc			@  f
+
+	.global kgdb_fiq_handler_end
+kgdb_fiq_handler_end:
-- 
1.7.10.4

Re: [PATCH 11/11] ARM: Get rid of .LCcralign local label usage in alignment_trap macro

[Anton Vorontsov]

On Mon, Jul 30, 2012 at 03:15:44PM +0100, Russell King - ARM Linux wrote:
> On Mon, Jul 30, 2012 at 04:58:20AM -0700, Anton Vorontsov wrote:
> > This makes the code more izolated.
> > 
> > The downside of this is that we now have an additional branch and the
> > code itself is 8 bytes longer. But on the bright side, this new layout
> > can be more cache friendly since cr_alignment address might be already
> > in the cache line (not that I measured anything, it's just fun to think
> > about it).
> 
> The caches are harvard, so mixing data and code together does not increase
> performance.  Having data which is used by the same code in the same cache
> line results in better performance.
> 
> The additional branch will also cause a pipeline stall on older CPUs.
> 
> So no, I don't see any way that this is a performance improvement.  Please
> leave this as is.

Sure, will drop it.

Thanks!

-- 
Anton Vorontsov
Email: cbouatmailru@gmail.com

Re: [PATCH 03/11] kdb: Implement disable_nmi command

[Anton Vorontsov]

On Mon, Jul 30, 2012 at 10:33:34AM -0700, Colin Cross wrote:
> On Mon, Jul 30, 2012 at 4:58 AM, Anton Vorontsov
> <anton.vorontsov@linaro.org> wrote:
> > This command disables NMI-entry. If NMI source was previously shared with
> > a serial console ("debug port"), this effectively releases the port from
> > KDB exclusive use, and makes the console available for normal use.
> >
> > Of course, NMI can be reenabled, enable_nmi modparam is used for that:
> >
> >         echo 1 > /sys/module/kdb/parameters/enable_nmi
> 
> This is very different behavior from the FIQ debugger "console"
> command you are trying to replace.  In the FIQ debugger, everything
> goes through the FIQ/NMI, even when in console mode.  That means that
> the user can always get back to FIQ debugger/KDB mode using a special
> sequence (we use a break character).  With your implementation, if you
> switch from KDB to console to see if the console is working, and find
> that it is not working, you can never get back into KDB.

Ah, I see. But with disable_nmi, in addition to kernel console,
applications can use /dev/ttyXX as normal, and with 'console' command
that is not possible (at least w/o modifying applications to escape
magic sequence). So, I think we should have both commands, each would
handle its own use case.

(Initially I just tried to avoid adding another console driver, but
it seems there is no other way, heh.)

Thanks!

-- 
Anton Vorontsov
Email: cbouatmailru@gmail.com