Messages in this thread | | | Date | Tue, 29 Mar 2011 12:02:19 -0700 | Subject | Re: [PATCH] ARM: Use generic BUG() handler | From | Simon Glass <> |
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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@chromium.org> wrote: > From: Simon Glass <sjg@google.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@chromium.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 > > -- 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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