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Date: Tue, 29 Mar 2011 12:02:19 -0700
From: Simon Glass <sjg@...omium.org>
To: linux-arm-kernel@...ts.infradead.org
Cc: Russell King <linux@....linux.org.uk>,
Tony Lindgren <tony@...mide.com>,
Nicolas Pitre <nicolas.pitre@...aro.org>,
Catalin Marinas <catalin.marinas@....com>,
Joe Perches <joe@...ches.com>,
Laurent Pinchart <laurent.pinchart@...asonboard.com>,
Alexander Shishkin <virtuoso@...nd.org>,
Phil Carmody <ext-phil.2.carmody@...ia.com>,
Rabin Vincent <rabin@....in>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: Use generic BUG() handler
Hi, does anyone have any more comments on this? Has anyone tried it
apart from anish kumar? Thanks, Simon
On Wed, Mar 16, 2011 at 1:27 PM, Simon Glass <sjg@...omium.org> wrote:
> From: Simon Glass <sjg@...gle.com>
>
> ARM uses its own BUG() handler which makes its output slightly different
> from other archtectures.
>
> One of the problems is that the ARM implementation doesn't report the function
> with the BUG() in it, but always reports the PC being in __bug(). The generic
> implementation doesn't have this problem.
>
> Currently we get something like:
>
> kernel BUG at fs/proc/breakme.c:35!
> Unable to handle kernel NULL pointer dereference at virtual address 00000000
> ...
> PC is at __bug+0x20/0x2c
>
> With this patch it displays:
>
> kernel BUG at fs/proc/breakme.c:35!
> Internal error: Oops - undefined instruction: 0 [#1] PREEMPT SMP
> ...
> PC is at write_breakme+0xd0/0x1b4
>
> This implementation uses an undefined instruction to implement BUG, and sets up
> a bug table containing the relevant information. Many version of gcc do not
> support %c properly for ARM (inserting a # when they shouldn't) so we work
> around this using distasteful macro magic.
>
> Also the backtrace the message now appears even when CONFIG_ARM_UNWIND is
> defined.
>
> You can fall back to the previous BUG implementation by making GENERIC_BUG
> default to n in arch/arm/Kconfig.
>
> Change-Id: I07d77c832e816f5ad2390e25f466ddf750adecf4
>
> Signed-off-by: Simon Glass <sjg@...omium.org>
> ---
> arch/arm/Kconfig | 4 +++
> arch/arm/include/asm/bug.h | 57 +++++++++++++++++++++++++++++++++++++++++
> arch/arm/kernel/traps.c | 24 +++++++++++++++++
> arch/arm/kernel/vmlinux.lds.S | 12 ++++++++
> 4 files changed, 97 insertions(+), 0 deletions(-)
>
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 166efa2..7c8f11c 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -191,6 +191,10 @@ config VECTORS_BASE
> help
> The base address of exception vectors.
>
> +config GENERIC_BUG
> + def_bool y
> + depends on BUG
> +
> source "init/Kconfig"
>
> source "kernel/Kconfig.freezer"
> diff --git a/arch/arm/include/asm/bug.h b/arch/arm/include/asm/bug.h
> index 4d88425..3f8a798 100644
> --- a/arch/arm/include/asm/bug.h
> +++ b/arch/arm/include/asm/bug.h
> @@ -3,6 +3,61 @@
>
>
> #ifdef CONFIG_BUG
> +
> +#ifdef CONFIG_GENERIC_BUG
> +
> +/*
> + * Use a suitable undefined instruction to use for ARM/Thumb2 bug handling.
> + * We need to be careful not to conflict with those used by other modules and
> + * the register_undef_hook() system.
> + */
> +#ifdef CONFIG_THUMB2_KERNEL
> +#define BUG_INSTR_VALUE 0xde02
> +#define BUG_INSTR_TYPE ".hword "
> +#else
> +#define BUG_INSTR_VALUE 0xe7f001f2
> +#define BUG_INSTR_TYPE ".word "
> +#endif
> +
> +
> +#define BUG() _BUG(__FILE__, __LINE__, BUG_INSTR_VALUE)
> +#define _BUG(file, line, value) __BUG(file, line, value)
> +
> +#ifdef CONFIG_DEBUG_BUGVERBOSE
> +
> +/*
> + * The extra indirection is to ensure that the __FILE__ string comes through
> + * OK. Many version of gcc do not support the asm %c parameter which would be
> + * preferable to this unpleasantness. We use mergeable string sections to
> + * avoid multiple copies of the string appearing in the kernel image.
> + */
> +
> +#define __BUG(__file, __line, __value) \
> +do { \
> + BUILD_BUG_ON(sizeof(struct bug_entry) != 12); \
> + asm volatile("1:\t" BUG_INSTR_TYPE #__value "\n" \
> + ".pushsection .rodata.str, \"aMS\", 1\n" \
> + "2:\t.asciz " #__file "\n" \
> + ".popsection\n" \
> + ".pushsection __bug_table,\"a\"\n" \
> + "3:\t.word 1b, 2b\n" \
> + "\t.hword " #__line ", 0\n" \
> + ".popsection"); \
> + unreachable(); \
> +} while (0)
> +
> +#else /* not CONFIG_DEBUG_BUGVERBOSE */
> +
> +#define __BUG(__file, __line, __value) \
> +do { \
> + asm volatile(BUG_INSTR_TYPE #__value); \
> + unreachable(); \
> +} while (0)
> +#endif /* CONFIG_DEBUG_BUGVERBOSE */
> +
> +
> +#else /* not CONFIG_GENERIC_BUG */
> +
> #ifdef CONFIG_DEBUG_BUGVERBOSE
> extern void __bug(const char *file, int line) __attribute__((noreturn));
>
> @@ -16,6 +71,8 @@ extern void __bug(const char *file, int line) __attribute__((noreturn));
>
> #endif
>
> +#endif /* CONFIG_GENERIC_BUG */
> +
> #define HAVE_ARCH_BUG
> #endif
>
> diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
> index ee57640..1199cfe 100644
> --- a/arch/arm/kernel/traps.c
> +++ b/arch/arm/kernel/traps.c
> @@ -21,6 +21,7 @@
> #include <linux/kdebug.h>
> #include <linux/module.h>
> #include <linux/kexec.h>
> +#include <linux/bug.h>
> #include <linux/delay.h>
> #include <linux/init.h>
>
> @@ -163,6 +164,7 @@ static void dump_instr(const char *lvl, struct pt_regs *regs)
> #ifdef CONFIG_ARM_UNWIND
> static inline void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
> {
> + printk("Backtrace: ");
> unwind_backtrace(regs, tsk);
> }
> #else
> @@ -271,6 +273,8 @@ void die(const char *str, struct pt_regs *regs, int err)
> spin_lock_irq(&die_lock);
> console_verbose();
> bust_spinlocks(1);
> + if (!user_mode(regs))
> + report_bug(regs->ARM_pc, regs);
> ret = __die(str, err, thread, regs);
>
> if (regs && kexec_should_crash(thread->task))
> @@ -302,6 +306,26 @@ void arm_notify_die(const char *str, struct pt_regs *regs,
> }
> }
>
> +#ifdef CONFIG_GENERIC_BUG
> +
> +int is_valid_bugaddr(unsigned long pc)
> +{
> +#ifdef CONFIG_THUMB2_KERNEL
> + unsigned short bkpt;
> +#else
> + unsigned long bkpt;
> +#endif
> +
> + if (pc < PAGE_OFFSET)
> + return 0;
> + if (probe_kernel_address((unsigned *)pc, bkpt))
> + return 0;
> +
> + return bkpt == BUG_INSTR_VALUE;
> +}
> +
> +#endif
> +
> static LIST_HEAD(undef_hook);
> static DEFINE_SPINLOCK(undef_lock);
>
> diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
> index 6146279..4f22346 100644
> --- a/arch/arm/kernel/vmlinux.lds.S
> +++ b/arch/arm/kernel/vmlinux.lds.S
> @@ -80,6 +80,18 @@ SECTIONS
>
> PERCPU(PAGE_SIZE)
>
> + /*
> + * .exit.text is discarded at runtime, not link time, to deal with
> + * references from bug_table
> + */
> + .exit.text : AT(ADDR(.exit.text)) {
> + EXIT_TEXT
> + }
> +
> + .exit.data : AT(ADDR(.exit.data)) {
> + EXIT_DATA
> + }
> +
> #ifndef CONFIG_XIP_KERNEL
> . = ALIGN(PAGE_SIZE);
> __init_end = .;
> --
> 1.7.3.1
>
>
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