Date: Fri, 18 Jul 2008 11:44:29 -0700
From: Deepak Saxena <dsaxena@plexity.net>
To: Jason Wessel <jason.wessel@windriver.com>
Cc: linux-kernel@vger.kernel.org, rmk@arm.linux.org.uk,
       linux-arm-kernel@lists.arm.linux.org.uk
Subject: Re: [PATCH 1/4] kgdb: support for ARCH=arm
Message-ID: <20080718184429.GA10770@plexity.net>
Reply-To: dsaxena@plexity.net
References: <1216124876-19108-1-git-send-email-jason.wessel@windriver.com> <1216124876-19108-2-git-send-email-jason.wessel@windriver.com>
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On Jul 15 2008, at 07:27, Jason Wessel was caught saying:
> 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.

Acked-By: Deepak Saxena <dsaxena@plexity.net>


> 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>
> ---
>  arch/arm/Kconfig         |    1 +
>  arch/arm/kernel/Makefile |    1 +
>  arch/arm/kernel/kgdb.c   |  201 ++++++++++++++++++++++++++++++++++++++++++++++
>  arch/arm/kernel/setup.c  |    2 +
>  arch/arm/kernel/traps.c  |    5 +
>  include/asm-arm/kgdb.h   |  104 ++++++++++++++++++++++++
>  include/asm-arm/traps.h  |    2 +
>  7 files changed, 316 insertions(+), 0 deletions(-)
>  create mode 100644 arch/arm/kernel/kgdb.c
>  create mode 100644 include/asm-arm/kgdb.h
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 258f136..fd4d803 100644
> --- a/arch/arm/Kconfig
> +++ b/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)
> diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
> index eb9092c..1d296fc 100644
> --- a/arch/arm/kernel/Makefile
> +++ b/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
> diff --git a/arch/arm/kernel/kgdb.c b/arch/arm/kernel/kgdb.c
> new file mode 100644
> index 0000000..aaffaec
> --- /dev/null
> +++ b/arch/arm/kernel/kgdb.c
> @@ -0,0 +1,201 @@
> +/*
> + * 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
> +};
> diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
> index b7b0720..38f0e79 100644
> --- a/arch/arm/kernel/setup.c
> +++ b/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();
>  }
>  
>  
> diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
> index 5595fdd..7277aef 100644
> --- a/arch/arm/kernel/traps.c
> +++ b/arch/arm/kernel/traps.c
> @@ -708,6 +708,11 @@ 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[];
>  	extern char __vectors_start[], __vectors_end[];
> diff --git a/include/asm-arm/kgdb.h b/include/asm-arm/kgdb.h
> new file mode 100644
> index 0000000..67af4b8
> --- /dev/null
> +++ b/include/asm-arm/kgdb.h
> @@ -0,0 +1,104 @@
> +/*
> + * 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__ */
> diff --git a/include/asm-arm/traps.h b/include/asm-arm/traps.h
> index f1541af..aa399ae 100644
> --- a/include/asm-arm/traps.h
> +++ b/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
> -- 
> 1.5.5.1
> 
> --
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