kgdb: support for ARCH=arm

This patch adds the ARCH=arm specific a kgdb backend, originally
written by Deepak Saxena <dsaxena@plexity.net> and George Davis
<gdavis@mvista.com>.  Geoff Levand <geoffrey.levand@am.sony.com>,
Nicolas Pitre, Manish Lachwani, and Jason Wessel have contributed
various fixups here as well.

The KGDB patch makes one change to the core ARM architecture such that
the traps are initialized early for use with the debugger or other
subsystems.

[ mingo@elte.hu: small cleanups. ]
[ ben-linux@fluff.org: fixed early_trap_init ]
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Acked-by: Deepak Saxena <dsaxena@plexity.net>

arch/arm/Kconfig

@@ -12,6 +12,7 @@ config ARM
 	select RTC_LIB
 	select SYS_SUPPORTS_APM_EMULATION
 	select HAVE_OPROFILE
+	select HAVE_ARCH_KGDB
 	select HAVE_KPROBES if (!XIP_KERNEL)
 	select HAVE_KRETPROBES if (HAVE_KPROBES)
 	select HAVE_FTRACE if (!XIP_KERNEL)

arch/arm/kernel/Makefile

@@ -28,6 +28,7 @@ obj-$(CONFIG_KPROBES)		+= kprobes.o kprobes-decode.o
 obj-$(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_CRUNCH)		+= crunch.o crunch-bits.o
 AFLAGS_crunch-bits.o		:= -Wa,-mcpu=ep9312

arch/arm/kernel/kgdb.c

+/*
+ * arch/arm/kernel/kgdb.c
+ *
+ * ARM KGDB support
+ *
+ * Copyright (c) 2002-2004 MontaVista Software, Inc
+ * Copyright (c) 2008 Wind River Systems, Inc.
+ *
+ * Authors:  George Davis <davis_g@mvista.com>
+ *           Deepak Saxena <dsaxena@plexity.net>
+ */
+#include <linux/kgdb.h>
+#include <asm/traps.h>
+
+/* Make a local copy of the registers passed into the handler (bletch) */
+void pt_regs_to_gdb_regs(unsigned long *gdb_regs, struct pt_regs *kernel_regs)
+{
+	int regno;
+
+	/* Initialize all to zero. */
+	for (regno = 0; regno < GDB_MAX_REGS; regno++)
+		gdb_regs[regno] = 0;
+
+	gdb_regs[_R0]		= kernel_regs->ARM_r0;
+	gdb_regs[_R1]		= kernel_regs->ARM_r1;
+	gdb_regs[_R2]		= kernel_regs->ARM_r2;
+	gdb_regs[_R3]		= kernel_regs->ARM_r3;
+	gdb_regs[_R4]		= kernel_regs->ARM_r4;
+	gdb_regs[_R5]		= kernel_regs->ARM_r5;
+	gdb_regs[_R6]		= kernel_regs->ARM_r6;
+	gdb_regs[_R7]		= kernel_regs->ARM_r7;
+	gdb_regs[_R8]		= kernel_regs->ARM_r8;
+	gdb_regs[_R9]		= kernel_regs->ARM_r9;
+	gdb_regs[_R10]		= kernel_regs->ARM_r10;
+	gdb_regs[_FP]		= kernel_regs->ARM_fp;
+	gdb_regs[_IP]		= kernel_regs->ARM_ip;
+	gdb_regs[_SPT]		= kernel_regs->ARM_sp;
+	gdb_regs[_LR]		= kernel_regs->ARM_lr;
+	gdb_regs[_PC]		= kernel_regs->ARM_pc;
+	gdb_regs[_CPSR]		= kernel_regs->ARM_cpsr;
+}
+
+/* Copy local gdb registers back to kgdb regs, for later copy to kernel */
+void gdb_regs_to_pt_regs(unsigned long *gdb_regs, struct pt_regs *kernel_regs)
+{
+	kernel_regs->ARM_r0	= gdb_regs[_R0];
+	kernel_regs->ARM_r1	= gdb_regs[_R1];
+	kernel_regs->ARM_r2	= gdb_regs[_R2];
+	kernel_regs->ARM_r3	= gdb_regs[_R3];
+	kernel_regs->ARM_r4	= gdb_regs[_R4];
+	kernel_regs->ARM_r5	= gdb_regs[_R5];
+	kernel_regs->ARM_r6	= gdb_regs[_R6];
+	kernel_regs->ARM_r7	= gdb_regs[_R7];
+	kernel_regs->ARM_r8	= gdb_regs[_R8];
+	kernel_regs->ARM_r9	= gdb_regs[_R9];
+	kernel_regs->ARM_r10	= gdb_regs[_R10];
+	kernel_regs->ARM_fp	= gdb_regs[_FP];
+	kernel_regs->ARM_ip	= gdb_regs[_IP];
+	kernel_regs->ARM_sp	= gdb_regs[_SPT];
+	kernel_regs->ARM_lr	= gdb_regs[_LR];
+	kernel_regs->ARM_pc	= gdb_regs[_PC];
+	kernel_regs->ARM_cpsr	= gdb_regs[_CPSR];
+}
+
+void
+sleeping_thread_to_gdb_regs(unsigned long *gdb_regs, struct task_struct *task)
+{
+	struct pt_regs *thread_regs;
+	int regno;
+
+	/* Just making sure... */
+	if (task == NULL)
+		return;
+
+	/* Initialize to zero */
+	for (regno = 0; regno < GDB_MAX_REGS; regno++)
+		gdb_regs[regno] = 0;
+
+	/* Otherwise, we have only some registers from switch_to() */
+	thread_regs		= task_pt_regs(task);
+	gdb_regs[_R0]		= thread_regs->ARM_r0;
+	gdb_regs[_R1]		= thread_regs->ARM_r1;
+	gdb_regs[_R2]		= thread_regs->ARM_r2;
+	gdb_regs[_R3]		= thread_regs->ARM_r3;
+	gdb_regs[_R4]		= thread_regs->ARM_r4;
+	gdb_regs[_R5]		= thread_regs->ARM_r5;
+	gdb_regs[_R6]		= thread_regs->ARM_r6;
+	gdb_regs[_R7]		= thread_regs->ARM_r7;
+	gdb_regs[_R8]		= thread_regs->ARM_r8;
+	gdb_regs[_R9]		= thread_regs->ARM_r9;
+	gdb_regs[_R10]		= thread_regs->ARM_r10;
+	gdb_regs[_FP]		= thread_regs->ARM_fp;
+	gdb_regs[_IP]		= thread_regs->ARM_ip;
+	gdb_regs[_SPT]		= thread_regs->ARM_sp;
+	gdb_regs[_LR]		= thread_regs->ARM_lr;
+	gdb_regs[_PC]		= thread_regs->ARM_pc;
+	gdb_regs[_CPSR]		= thread_regs->ARM_cpsr;
+}
+
+static int compiled_break;
+
+int kgdb_arch_handle_exception(int exception_vector, int signo,
+			       int err_code, char *remcom_in_buffer,
+			       char *remcom_out_buffer,
+			       struct pt_regs *linux_regs)
+{
+	unsigned long addr;
+	char *ptr;
+
+	switch (remcom_in_buffer[0]) {
+	case 'D':
+	case 'k':
+	case 'c':
+		kgdb_contthread = NULL;
+
+		/*
+		 * Try to read optional parameter, pc unchanged if no parm.
+		 * If this was a compiled breakpoint, we need to move
+		 * to the next instruction or we will just breakpoint
+		 * over and over again.
+		 */
+		ptr = &remcom_in_buffer[1];
+		if (kgdb_hex2long(&ptr, &addr))
+			linux_regs->ARM_pc = addr;
+		else if (compiled_break == 1)
+			linux_regs->ARM_pc += 4;
+
+		compiled_break = 0;
+
+		return 0;
+	}
+
+	return -1;
+}
+
+static int kgdb_brk_fn(struct pt_regs *regs, unsigned int instr)
+{
+	kgdb_handle_exception(1, SIGTRAP, 0, regs);
+
+	return 0;
+}
+
+static int kgdb_compiled_brk_fn(struct pt_regs *regs, unsigned int instr)
+{
+	compiled_break = 1;
+	kgdb_handle_exception(1, SIGTRAP, 0, regs);
+
+	return 0;
+}
+
+static struct undef_hook kgdb_brkpt_hook = {
+	.instr_mask		= 0xffffffff,
+	.instr_val		= KGDB_BREAKINST,
+	.fn			= kgdb_brk_fn
+};
+
+static struct undef_hook kgdb_compiled_brkpt_hook = {
+	.instr_mask		= 0xffffffff,
+	.instr_val		= KGDB_COMPILED_BREAK,
+	.fn			= kgdb_compiled_brk_fn
+};
+
+/**
+ *	kgdb_arch_init - Perform any architecture specific initalization.
+ *
+ *	This function will handle the initalization of any architecture
+ *	specific callbacks.
+ */
+int kgdb_arch_init(void)
+{
+	register_undef_hook(&kgdb_brkpt_hook);
+	register_undef_hook(&kgdb_compiled_brkpt_hook);
+
+	return 0;
+}
+
+/**
+ *	kgdb_arch_exit - Perform any architecture specific uninitalization.
+ *
+ *	This function will handle the uninitalization of any architecture
+ *	specific callbacks, for dynamic registration and unregistration.
+ */
+void kgdb_arch_exit(void)
+{
+	unregister_undef_hook(&kgdb_brkpt_hook);
+	unregister_undef_hook(&kgdb_compiled_brkpt_hook);
+}
+
+/*
+ * Register our undef instruction hooks with ARM undef core.
+ * We regsiter a hook specifically looking for the KGB break inst
+ * and we handle the normal undef case within the do_undefinstr
+ * handler.
+ */
+struct kgdb_arch arch_kgdb_ops = {
+#ifndef __ARMEB__
+	.gdb_bpt_instr		= {0xfe, 0xde, 0xff, 0xe7}
+#else /* ! __ARMEB__ */
+	.gdb_bpt_instr		= {0xe7, 0xff, 0xde, 0xfe}
+#endif
+};

arch/arm/kernel/setup.c

@@ -36,6 +36,7 @@
 #include <asm/mach/arch.h>
 #include <asm/mach/irq.h>
 #include <asm/mach/time.h>
+#include <asm/traps.h>
 
 #include "compat.h"
 #include "atags.h"
@@ -853,6 +854,7 @@ void __init setup_arch(char **cmdline_p)
 	conswitchp = &dummy_con;
 #endif
 #endif
+	early_trap_init();
 }
 
 

arch/arm/kernel/traps.c

@@ -707,6 +707,11 @@ void abort(void)
 EXPORT_SYMBOL(abort);
 
 void __init trap_init(void)
+{
+	return;
+}
+
+void __init early_trap_init(void)
 {
 	unsigned long vectors = CONFIG_VECTORS_BASE;
 	extern char __stubs_start[], __stubs_end[];

include/asm-arm/kgdb.h

+/*
+ * ARM KGDB support
+ *
+ * Author: Deepak Saxena <dsaxena@mvista.com>
+ *
+ * Copyright (C) 2002 MontaVista Software Inc.
+ *
+ */
+
+#ifndef __ARM_KGDB_H__
+#define __ARM_KGDB_H__
+
+#include <linux/ptrace.h>
+
+/*
+ * GDB assumes that we're a user process being debugged, so
+ * it will send us an SWI command to write into memory as the
+ * debug trap. When an SWI occurs, the next instruction addr is
+ * placed into R14_svc before jumping to the vector trap.
+ * This doesn't work for kernel debugging as we are already in SVC
+ * we would loose the kernel's LR, which is a bad thing. This
+ * is  bad thing.
+ *
+ * By doing this as an undefined instruction trap, we force a mode
+ * switch from SVC to UND mode, allowing us to save full kernel state.
+ *
+ * We also define a KGDB_COMPILED_BREAK which can be used to compile
+ * in breakpoints. This is important for things like sysrq-G and for
+ * the initial breakpoint from trap_init().
+ *
+ * Note to ARM HW designers: Add real trap support like SH && PPC to
+ * make our lives much much simpler. :)
+ */
+#define BREAK_INSTR_SIZE	4
+#define GDB_BREAKINST		0xef9f0001
+#define KGDB_BREAKINST		0xe7ffdefe
+#define KGDB_COMPILED_BREAK	0xe7ffdeff
+#define CACHE_FLUSH_IS_SAFE	1
+
+#ifndef	__ASSEMBLY__
+
+static inline void arch_kgdb_breakpoint(void)
+{
+	asm(".word 0xe7ffdeff");
+}
+
+extern void kgdb_handle_bus_error(void);
+extern int kgdb_fault_expected;
+
+#endif /* !__ASSEMBLY__ */
+
+/*
+ * From Kevin Hilman:
+ *
+ * gdb is expecting the following registers layout.
+ *
+ * r0-r15: 1 long word each
+ * f0-f7:  unused, 3 long words each !!
+ * fps:    unused, 1 long word
+ * cpsr:   1 long word
+ *
+ * Even though f0-f7 and fps are not used, they need to be
+ * present in the registers sent for correct processing in
+ * the host-side gdb.
+ *
+ * In particular, it is crucial that CPSR is in the right place,
+ * otherwise gdb will not be able to correctly interpret stepping over
+ * conditional branches.
+ */
+#define _GP_REGS		16
+#define _FP_REGS		8
+#define _EXTRA_REGS		2
+#define GDB_MAX_REGS		(_GP_REGS + (_FP_REGS * 3) + _EXTRA_REGS)
+
+#define KGDB_MAX_NO_CPUS	1
+#define BUFMAX			400
+#define NUMREGBYTES		(GDB_MAX_REGS << 2)
+#define NUMCRITREGBYTES		(32 << 2)
+
+#define _R0			0
+#define _R1			1
+#define _R2			2
+#define _R3			3
+#define _R4			4
+#define _R5			5
+#define _R6			6
+#define _R7			7
+#define _R8			8
+#define _R9			9
+#define _R10			10
+#define _FP			11
+#define _IP			12
+#define _SPT			13
+#define _LR			14
+#define _PC			15
+#define _CPSR			(GDB_MAX_REGS - 1)
+
+/*
+ * So that we can denote the end of a frame for tracing,
+ * in the simple case:
+ */
+#define CFI_END_FRAME(func)	__CFI_END_FRAME(_PC, _SPT, func)
+
+#endif /* __ASM_KGDB_H__ */

include/asm-arm/traps.h

@@ -24,4 +24,6 @@ static inline int in_exception_text(unsigned long ptr)
 	       ptr < (unsigned long)&__exception_text_end;
 }
 
+extern void __init early_trap_init(void);
+
 #endif