Re: [RFC PATCH] ARM: Use generic BUG() handler

From: Dave Martin
Date: Tue Mar 01 2011 - 12:48:30 EST

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On Tue, Mar 1, 2011 at 12:27 AM, Simon Glass <sjg@xxxxxxxxxxxx> wrote:
> I am looking for comments please on this patch.
>
> 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.
>
> Also backtraces were reported slightly differently - so I have added a newline
> after the backtrace message, a space before the address, and ensured that the
> message appears even when CONFIG_ARM_UNWIND is defined. These are aimed at
> consistency between architectures, and may or may not be acceptable for ARM.
> In any case they may be best as a separate patch.
>
> Change-Id: I515db9a04e98084e6bbb21c4a1d13579568a0904
>
> Signed-off-by: Simon Glass <sjg@xxxxxxxxxxxx>
> ---
> arch/arm/Kconfig | 4 ++++
> arch/arm/include/asm/bug.h | 40 +++++++++++++++++++++++++++++++++++++++-
> arch/arm/kernel/traps.c | 21 +++++++++++++++++++--
> arch/arm/kernel/unwind.c | 1 +
> arch/arm/kernel/vmlinux.lds.S | 15 +++++++++++++--
> 5 files changed, 76 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 26d45e5..d4fb0fb 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..bbbebe4 100644
> --- a/arch/arm/include/asm/bug.h
> +++ b/arch/arm/include/asm/bug.h
> @@ -3,6 +3,40 @@
>
>
> #ifdef CONFIG_BUG
> +
> +#ifdef CONFIG_GENERIC_BUG
> +
> +
> +/* A suitable undefined instruction to use for ARM bug handling */
> +#define BUG_INSTR_ARM 0xec000000

This will need a suitable separate definition for
CONFIG_THUMB2_KERNEL, where the instruction encodings are different.

It may also be a good idea to include the whole directive, e.g.
#define BUG_INSTR_ARM ".word 0xec000000"
...since for Thumb you probably want to use .hword/.short (or
inst.n/inst.w if we consider that everyone has new enough tools)
instead of .long in that case.

> +
> +
> +#ifdef CONFIG_DEBUG_BUGVERBOSE
> +#define BUG() \
> +do { \
> + asm volatile("1:\t.word %c3\n" \
> + ".pushsection __bug_table,\"a\"\n" \
> + "2:\t.word 1b, %c0\n" \
> + "\t.hword %c1, 0\n" \
> + "\t.org 2b+%c2\n" \
> + ".popsection" \
> + : \
> + : "i" (__FILE__), "i" (__LINE__), \
> + "i" (sizeof(struct bug_entry)), \
> + "i" (BUG_INSTR_ARM)); \
> + unreachable(); \
> +} while (0)
> +
> +#else
> +#define BUG() \
> +do { \
> + asm volatile("ud2"); \
> + unreachable(); \
> +} while (0)
> +#endif
> +
> +#else /* not CONFIG_GENERIC_BUG */
> +
> #ifdef CONFIG_DEBUG_BUGVERBOSE
> extern void __bug(const char *file, int line) __attribute__((noreturn));
>
> @@ -16,8 +50,12 @@ extern void __bug(const char *file, int line) __attribute__((noreturn));
>
> #endif
>
> +#endif /* CONFIG_GENERIC_BUG */
> +
> #define HAVE_ARCH_BUG
> -#endif
> +
> +#endif /* CONFIG_BUG */
> +
>
> #include <asm-generic/bug.h>
>
> diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
> index ee57640..d5e5df9 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>
>
> @@ -55,7 +56,8 @@ static void dump_mem(const char *, const char *, unsigned long, unsigned long);
> void dump_backtrace_entry(unsigned long where, unsigned long from, unsigned long frame)
> {
> #ifdef CONFIG_KALLSYMS
> - printk("[<%08lx>] (%pS) from [<%08lx>] (%pS)\n", where, (void *)where, from, (void *)from);
> + printk(" [<%08lx>] (%pS) from [<%08lx>] (%pS)\n", where, (void *)where,
> + from, (void *)from);
> #else
> printk("Function entered at [<%08lx>] from [<%08lx>]\n", where, from);
> #endif
> @@ -171,7 +173,7 @@ static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
> unsigned int fp, mode;
> int ok = 1;
>
> - printk("Backtrace: ");
> + printk("Backtrace:\n");
>
> if (!tsk)
> tsk = current;
> @@ -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 +306,19 @@ void arm_notify_die(const char *str, struct pt_regs *regs,
> }
> }
>
> +int is_valid_bugaddr(unsigned long pc)
> +{
> + unsigned bkpt;
> +
> + if (pc < PAGE_OFFSET)
> + return 0;
> + if (probe_kernel_address((unsigned *)pc, bkpt))
> + return 0;
> +
> + return bkpt == BUG_INSTR_ARM;
> +}
> +
> +
> static LIST_HEAD(undef_hook);
> static DEFINE_SPINLOCK(undef_lock);
>
> diff --git a/arch/arm/kernel/unwind.c b/arch/arm/kernel/unwind.c
> index d2cb0b3..3f065bd 100644
> --- a/arch/arm/kernel/unwind.c
> +++ b/arch/arm/kernel/unwind.c
> @@ -355,6 +355,7 @@ void unwind_backtrace(struct pt_regs *regs, struct task_struct *tsk)
> register unsigned long current_sp asm ("sp");
>
> pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
> + printk("Backtrace:\n");
>
> if (!tsk)
> tsk = current;
> diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
> index 86b66f3..591ab50 100644
> --- a/arch/arm/kernel/vmlinux.lds.S
> +++ b/arch/arm/kernel/vmlinux.lds.S
> @@ -72,6 +72,18 @@ 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 = .;
> @@ -246,7 +258,6 @@ SECTIONS
> __tcm_end = .;
> }
> #endif
> -
> BSS_SECTION(0, 0, 0)
> _end = .;
>
> @@ -254,7 +265,7 @@ SECTIONS
> .comment 0 : { *(.comment) }
>
> /* Default discards */
> - DISCARDS
> + /*DISCARDS*/
>
> #ifndef CONFIG_SMP_ON_UP
> /DISCARD/ : {
> --
> 1.7.3.1
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>
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Next message: Gary Hade: "matroxfb: remove incorrect Matrox G200eV support"
Previous message: Aaro Koskinen: "Re: [GIT PULL] omap fixes for v2.6.38-rc6"
In reply to: Dave Martin: "Re: [RFC PATCH] ARM: Use generic BUG() handler"
Next in thread: Russell King - ARM Linux: "Re: [RFC PATCH] ARM: Use generic BUG() handler"
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