Re: [PATCH 7/7] powerpc/traps: Show instructions on exceptions

LEROY Christophe
2018-07-25T16:01:39Z

Murilo Opsfelder Araujo <muriloo@linux.ibm.com> a écrit :

> Move show_instructions() declaration to arch/powerpc/include/asm/stacktrace.h
> and include asm/stracktrace.h in arch/powerpc/kernel/process.c,
> which contains
> the implementation.
>
> Modify show_instructions() not to call __kernel_text_address(), allowing
> userspace instruction dump. probe_kernel_address(), which returns -EFAULT if
> something goes wrong, is still being called.
>
> Call show_instructions() in arch/powerpc/kernel/traps.c to dump
> instructions at
> faulty location, useful to debugging.

Shouldn't this part be in a second patch ?

Wouldn't it be better to also see regs in addition if we want to use
this to understand what happened ?
So you could call show_regs() instead of show_instructions() ?

Christophe

>
> Before this patch, an unhandled signal message looked like:
>
> Jul 24 09:57:00 localhost kernel: pandafault[10524]: segfault
> (11) at 00000000100007d0 nip 000000001000061c lr 00007fffbd295100
> code 2 in pandafault[10000000+10000]
>
> After this patch, it looks like:
>
> Jul 24 09:57:00 localhost kernel: pandafault[10524]: segfault
> (11) at 00000000100007d0 nip 000000001000061c lr 00007fffbd295100
> code 2 in pandafault[10000000+10000]
> Jul 24 09:57:00 localhost kernel: Instruction dump:
> Jul 24 09:57:00 localhost kernel: 4bfffeec 4bfffee8 3c401002
> 38427f00 fbe1fff8 f821ffc1 7c3f0b78 3d22fffe
> Jul 24 09:57:00 localhost kernel: 392988d0 f93f0020 e93f0020
> 39400048 <99490000> 39200000 7d234b78 383f0040
>
> Signed-off-by: Murilo Opsfelder Araujo <muriloo@linux.ibm.com>
> ---
> arch/powerpc/include/asm/stacktrace.h | 7 +++++++
> arch/powerpc/kernel/process.c | 6 +++---
> arch/powerpc/kernel/traps.c | 3 +++
> 3 files changed, 13 insertions(+), 3 deletions(-)
> create mode 100644 arch/powerpc/include/asm/stacktrace.h
>
> diff --git a/arch/powerpc/include/asm/stacktrace.h
> b/arch/powerpc/include/asm/stacktrace.h
> new file mode 100644
> index 000000000000..46e5ef451578
> --- /dev/null
> +++ b/arch/powerpc/include/asm/stacktrace.h
> @@ -0,0 +1,7 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _ASM_POWERPC_STACKTRACE_H
> +#define _ASM_POWERPC_STACKTRACE_H
> +
> +void show_instructions(struct pt_regs *regs);
> +
> +#endif /* _ASM_POWERPC_STACKTRACE_H */
> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> index b1af3390249c..ee1d63e03c52 100644
> --- a/arch/powerpc/kernel/process.c
> +++ b/arch/powerpc/kernel/process.c
> @@ -52,6 +52,7 @@
> #include <asm/machdep.h>
> #include <asm/time.h>
> #include <asm/runlatch.h>
> +#include <asm/stacktrace.h>
> #include <asm/syscalls.h>
> #include <asm/switch_to.h>
> #include <asm/tm.h>
> @@ -1261,7 +1262,7 @@ struct task_struct *__switch_to(struct
> task_struct *prev,
>
> static int instructions_to_print = 16;
>
> -static void show_instructions(struct pt_regs *regs)
> +void show_instructions(struct pt_regs *regs)
> {
> int i;
> unsigned long pc = regs->nip - (instructions_to_print * 3 / 4 *
> @@ -1283,8 +1284,7 @@ static void show_instructions(struct pt_regs *regs)
> pc = (unsigned long)phys_to_virt(pc);
> #endif
>
> - if (!__kernel_text_address(pc) ||
> - probe_kernel_address((unsigned int __user *)pc, instr)) {
> + if (probe_kernel_address((unsigned int __user *)pc, instr)) {
> pr_cont("XXXXXXXX ");
> } else {
> if (regs->nip == pc)
> diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
> index e55ee639d010..3beca17ac1b1 100644
> --- a/arch/powerpc/kernel/traps.c
> +++ b/arch/powerpc/kernel/traps.c
> @@ -70,6 +70,7 @@
> #include <asm/hmi.h>
> #include <sysdev/fsl_pci.h>
> #include <asm/kprobes.h>
> +#include <asm/stacktrace.h>
>
> #if defined(CONFIG_DEBUGGER) || defined(CONFIG_KEXEC_CORE)
> int (*__debugger)(struct pt_regs *regs) __read_mostly;
> @@ -357,6 +358,8 @@ static void show_signal_msg(int signr, struct
> pt_regs *regs, int code,
> print_vma_addr(KERN_CONT " in ", regs->nip);
>
> pr_cont("\n");
> +
> + show_instructions(regs);
> }
>
> void _exception_pkey(int signr, struct pt_regs *regs, int code,
> --
> 2.17.1