Messages in this thread Patch in this message | | | Date | Tue, 1 Mar 2011 17:48:21 +0000 | Subject | Re: [RFC PATCH] ARM: Use generic BUG() handler | From | Dave Martin <> |
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On Tue, Mar 1, 2011 at 12:27 AM, Simon Glass <sjg@chromium.org> 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@chromium.org> > --- > 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@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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