Discussion:
[Kgdb-bugreport] [PATCH 3/6] ARM: Move some macros from entry-armv to entry-header
Anton Vorontsov
2012-07-05 23:12:37 UTC
Permalink
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 <***@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
Anton Vorontsov
2012-07-05 23:12:40 UTC
Permalink
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 <***@linaro.org>
---
arch/arm/mach-versatile/Makefile | 1 +
arch/arm/mach-versatile/include/mach/irqs.h | 1 +
arch/arm/mach-versatile/kgdb_fiq.c | 40 +++++++++++++++++++++++++++
3 files changed, 42 insertions(+)
create mode 100644 arch/arm/mach-versatile/kgdb_fiq.c

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..c82e8ce
--- /dev/null
+++ b/arch/arm/mach-versatile/kgdb_fiq.c
@@ -0,0 +1,40 @@
+/*
+ * KGDB FIQ entry board/IC support
+ *
+ * Copyright 2012 Linaro Ltd.
+ * 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/types.h>
+#include <linux/kgdb.h>
+#include <mach/hardware.h>
+#include <mach/platform.h>
+#include <asm/kgdb.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 bool is_kgdb_nmi(void)
+{
+ return vic_is_fiq_rised(kgdb_fiq);
+}
+
+void kgdb_arch_enable_nmi(bool on)
+{
+ vic_fiq_select(kgdb_fiq, on);
+}
+
+static int kgdb_fiq_init(void)
+{
+ kgdb_fiq += INT_UARTINT0;
+ kgdb_register_nmi(is_kgdb_nmi);
+ return 0;
+}
+console_initcall(kgdb_fiq_init);
--
1.7.10.4
Anton Vorontsov
2012-07-05 23:12:39 UTC
Permalink
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 <***@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
Anton Vorontsov
2012-07-05 23:12:35 UTC
Permalink
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 <***@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
Anton Vorontsov
2012-07-05 23:12:36 UTC
Permalink
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 <***@linaro.org>
---
include/linux/kgdb.h | 9 +++++++++
kernel/debug/debug_core.c | 12 +++++++++++-
2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h
index c4d2fc1..47e739e 100644
--- a/include/linux/kgdb.h
+++ b/include/linux/kgdb.h
@@ -221,6 +221,15 @@ 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().
+ */
+extern void 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..e285600 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -214,6 +214,10 @@ int __weak kgdb_skipexception(int exception, struct pt_regs *regs)
return 0;
}

+void __weak kgdb_arch_enable_nmi(bool on)
+{
+}
+
/*
* Some architectures need cache flushes when we set/clear a
* breakpoint:
@@ -672,6 +676,9 @@ 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 +692,10 @@ 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
Anton Vorontsov
2012-07-05 23:12:38 UTC
Permalink
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 <***@linaro.org>
---
arch/arm/Kconfig | 14 +++++++
arch/arm/include/asm/kgdb.h | 8 ++++
arch/arm/kernel/Makefile | 1 +
arch/arm/kernel/kgdb_fiq.c | 78 +++++++++++++++++++++++++++++++++++++
arch/arm/kernel/kgdb_fiq_entry.S | 80 ++++++++++++++++++++++++++++++++++++++
5 files changed, 181 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..bc558d1 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -172,6 +172,20 @@ config GENERIC_ISA_DMA
config FIQ
bool

+config KGDB_FIQ
+ bool "KGDB/KDB FIQ debugger"
+ 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..ee51024 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);
+typedef bool (*is_kgdb_nmi_fn)(void);
+extern void kgdb_register_nmi(is_kgdb_nmi_fn is_kgdb_nmi);
+
#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..287504d
--- /dev/null
+++ b/arch/arm/kernel/kgdb_fiq.c
@@ -0,0 +1,78 @@
+/*
+ * KGDB FIQ entry
+ *
+ * Copyright 2010 Google, Inc.
+ * Arve Hjønnevåg <***@android.com>
+ * Colin Cross <***@android.com>
+ * Copyright 2012 Linaro Ltd.
+ * 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/slab.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 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;
+}
+
+static is_kgdb_nmi_fn is_kgdb_nmi;
+
+asmlinkage void __exception_irq_entry kgdb_fiq_do_handle(struct pt_regs *regs)
+{
+ if (!is_kgdb_nmi())
+ return;
+
+ nmi_enter();
+ kgdb_handle_exception(1, 0, 0, regs);
+ nmi_exit();
+}
+
+static struct fiq_handler kgdb_fiq_desc = {
+ .name = "kgdb",
+};
+
+void kgdb_register_nmi(is_kgdb_nmi_fn _is_kgdb_nmi)
+{
+ int err;
+ int cpu;
+
+ if (!kgdb_fiq_enabled)
+ return;
+
+ is_kgdb_nmi = _is_kgdb_nmi;
+
+ err = claim_fiq(&kgdb_fiq_desc);
+ if (err) {
+ WARN_ON(1);
+ return;
+ }
+
+ 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);
+}
diff --git a/arch/arm/kernel/kgdb_fiq_entry.S b/arch/arm/kernel/kgdb_fiq_entry.S
new file mode 100644
index 0000000..8524671
--- /dev/null
+++ b/arch/arm/kernel/kgdb_fiq_entry.S
@@ -0,0 +1,80 @@
+/*
+ * KGDB FIQ entry
+ *
+ * Copyright 1996,1997,1998 Russell King.
+ * Copyright 2012 Linaro Ltd.
+ * 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
+
+ .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
+ @ This is needed for kuser_cmpxchg_check/alignment_trap
+ .global cr_alignment
+.LCcralign:
+ .word cr_alignment
+
+.LCdohandle:
+ .long kgdb_fiq_do_handle
+
+ .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
Anton Vorontsov
2012-07-13 09:49:54 UTC
Permalink
On Thu, Jul 05, 2012 at 05:02:12PM -0700, Colin Cross wrote:
[...]
KGDB can obviously only be enabled on development
devices, although perhaps a more limited KDB could be left enabled.
Um, I would argue about 'obviously'. :-) It doesn't require
CONFIG_DEBUG_INFO (-g) or something like this, so if the concern is
the size (which is about 30..40 KB), then it is all manageable. If we
want it to be smaller, we should just work on making KGDB/KDB more
modular, so that we can exclude non-production features.
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.
Unfortunately, FIQs have been repurposed as secure interrupts on every
ARM SoC that supports TrustZone, which is basically all of the latest
generation, as well as a few of the previous generation. When an FIQ
arrives, the cpu traps into the secure mode, generally running a
separate secure OS written by a 3rd party vendor. We've tried to get
some SoC secure implementations to drop out of secure mode and into
the FIQ exception vector for specific irqs, with the registers set up
to allow the FIQ handler to return back to the original execution
point, but it's been successful.
It's pity, and this just shows that recent SOCs have a somewhat limited
debugging facilities. There are countless times when I was able to debug
a hang simply by hitting an NMI button on a reference board (not ARM,
tho) and just reading the trace.

Having any (even a watchdog) NMI connected to a kernel would be enough
to make things better. Btw, these patches' approach works even if we
can't reroute arbitrary interrupts to FIQs (like we do for serial lines).

[...]
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.
I think it could be an issue if KDB stopped execution whenever it
received any character. 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.
Aha, that's the real use-case, thanks! I started hacking the KDB
to add the async shell support, but then I realized that we still
don't need all the complexity. If the only purpose is to be safe from
the noise, then we can just do "knocking" before entering the debugger.

The thing is, we even have a standard sequence for entering KDB,
it is GDB-protocol command $3#33, so it actually makes sense to
implement this. This would be the only async command, and it doesn't
affect anything but the new code. I prepared a separate patch for this.

[...]
One of the nice features in FIQ debugger is the "console" command,
which causes all incoming serial characters to get passed to a console
device provided by the FIQ debugger, and characters from the console
to go out the serial port (when it is enabled). That way you can
still have the console when you want it, but only one driver talking
to the hardware.
This is surely a nice feature, and we have a chance to make it work
with this scheme too. For example, we can reroute FIQ to IRQ, and
reinitialize the tty device, so that it would grab the IRQ, then we
can give uart back. Surely there are some implementation details
that makes it not that easy, but it is definitely doable.

Thanks!
--
Anton Vorontsov
Email: ***@gmail.com
Anton Vorontsov
2012-07-13 22:10:56 UTC
Permalink
On Fri, Jul 13, 2012 at 09:43:45AM -0700, Colin Cross wrote:
[...]
I was referring to the security implications, not size. Leaving KDB
on is effectively instant root access over the serial console.
Oh, I see. Yes, for this we'd need to disable all modification commands.

[...]
Post by Anton Vorontsov
The thing is, we even have a standard sequence for entering KDB,
it is GDB-protocol command $3#33, so it actually makes sense to
implement this. This would be the only async command, and it doesn't
affect anything but the new code. I prepared a separate patch for this.
I would suggest making the sequence longer than just return. A single
character is not that unlikely to be generated by random noise - I've
seen multiple devices reboot when the serial console was connected
because it received a SysRq-Crash (a break is all zeroes, which is
very common while shorting the lines as the console is plugged in, and
then random noise sent a 'c').
No no, it's not just return. It is either return or the longer '$3#33'
escape sequence. Default is $3#33, so it should be pretty safe (but of
course we can make it even longer, or even configurable).

Thanks,
--
Anton Vorontsov
Email: ***@gmail.com
Colin Cross
2012-07-13 16:43:52 UTC
Permalink
On Fri, Jul 13, 2012 at 2:49 AM, Anton Vorontsov
Post by Anton Vorontsov
[...]
KGDB can obviously only be enabled on development
devices, although perhaps a more limited KDB could be left enabled.
Um, I would argue about 'obviously'. :-) It doesn't require
CONFIG_DEBUG_INFO (-g) or something like this, so if the concern is
the size (which is about 30..40 KB), then it is all manageable. If we
want it to be smaller, we should just work on making KGDB/KDB more
modular, so that we can exclude non-production features.
I was referring to the security implications, not size. Leaving KDB
on is effectively instant root access over the serial console.

<snip
Post by Anton Vorontsov
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.
I think it could be an issue if KDB stopped execution whenever it
received any character. 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.
Aha, that's the real use-case, thanks! I started hacking the KDB
to add the async shell support, but then I realized that we still
don't need all the complexity. If the only purpose is to be safe from
the noise, then we can just do "knocking" before entering the debugger.
The thing is, we even have a standard sequence for entering KDB,
it is GDB-protocol command $3#33, so it actually makes sense to
implement this. This would be the only async command, and it doesn't
affect anything but the new code. I prepared a separate patch for this.
I would suggest making the sequence longer than just return. A single
character is not that unlikely to be generated by random noise - I've
seen multiple devices reboot when the serial console was connected
because it received a SysRq-Crash (a break is all zeroes, which is
very common while shorting the lines as the console is plugged in, and
then random noise sent a 'c').

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