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SubjectRe: [PATCH v4 5/6] powerpc: Add show_user_instructions()
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Hi Murilo,

Le 03/08/2018 à 02:42, Murilo Opsfelder Araujo a écrit :
> Hi, Christophe.
>
> On Thu, Aug 02, 2018 at 07:26:20AM +0200, Christophe LEROY wrote:
>>
>>
>> Le 01/08/2018 à 23:33, Murilo Opsfelder Araujo a écrit :
>>> show_user_instructions() is a slightly modified version of
>>> show_instructions() that allows userspace instruction dump.
>>>
>>> This will be useful within show_signal_msg() to dump userspace
>>> instructions of the faulty location.
>>>
>>> Here is a sample of what show_user_instructions() outputs:
>>>
>>> pandafault[10850]: code: 4bfffeec 4bfffee8 3c401002 38427f00 fbe1fff8 f821ffc1 7c3f0b78 3d22fffe
>>> pandafault[10850]: code: 392988d0 f93f0020 e93f0020 39400048 <99490000> 39200000 7d234b78 383f0040
>>>
>>> The current->comm and current->pid printed can serve as a glue that
>>> links the instructions dump to its originator, allowing messages to be
>>> interleaved in the logs.
>>>
>>> Signed-off-by: Murilo Opsfelder Araujo <muriloo@linux.ibm.com>
>>> ---
>>> arch/powerpc/include/asm/stacktrace.h | 13 +++++++++
>>> arch/powerpc/kernel/process.c | 40 +++++++++++++++++++++++++++
>>> 2 files changed, 53 insertions(+)
>>> 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..6149b53b3bc8
>>> --- /dev/null
>>> +++ b/arch/powerpc/include/asm/stacktrace.h
>>> @@ -0,0 +1,13 @@
>>> +/* SPDX-License-Identifier: GPL-2.0 */
>>> +/*
>>> + * Stack trace functions.
>>> + *
>>> + * Copyright 2018, Murilo Opsfelder Araujo, IBM Corporation.
>>> + */
>>> +
>>> +#ifndef _ASM_POWERPC_STACKTRACE_H
>>> +#define _ASM_POWERPC_STACKTRACE_H
>>> +
>>> +void show_user_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 e9533b4d2f08..364645ac732c 100644
>>> --- a/arch/powerpc/kernel/process.c
>>> +++ b/arch/powerpc/kernel/process.c
>>> @@ -1299,6 +1299,46 @@ static void show_instructions(struct pt_regs *regs)
>>> pr_cont("\n");
>>> }
>>> +void show_user_instructions(struct pt_regs *regs)
>>> +{
>>> + int i;
>>> + const char *prefix = KERN_INFO "%s[%d]: code: ";
>>> + unsigned long pc = regs->nip - (instructions_to_print * 3 / 4 *
>>> + sizeof(int));
>>> +
>>> + printk(prefix, current->comm, current->pid);
>>
>> Why not use pr_info() and remove KERN_INFO from *prefix ?
>
> Because it doesn't compile:
>
> arch/powerpc/kernel/process.c:1317:10: error: expected ‘)’ before ‘prefix’
> pr_info(prefix, current->comm, current->pid);
> ^
> ./include/linux/printk.h:288:21: note: in definition of macro ‘pr_fmt’
> #define pr_fmt(fmt) fmt
> ^
>
> `pr_info(prefix, ...)` expands to `printk("\001" "6" prefix, ...)`,
> which is an invalid string concatenation.
>
> `pr_info("%s", ...)` expands to `printk("\001" "6" "%s", ...)`, which is
> valid.

Then what about using directly:

pr_info("%s[%d]: code: ", ...);

>
>>> +
>>> + for (i = 0; i < instructions_to_print; i++) {
>>> + int instr;
>>> +
>>> + if (!(i % 8) && (i > 0)) {
>>> + pr_cont("\n");
>>> + printk(prefix, current->comm, current->pid);
>>> + }
>>> +
>>> +#if !defined(CONFIG_BOOKE)
>>> + /* If executing with the IMMU off, adjust pc rather
>>> + * than print XXXXXXXX.
>>> + */
>>> + if (!(regs->msr & MSR_IR))
>>> + pc = (unsigned long)phys_to_virt(pc);
>>
>> Shouldn't this be done outside of the loop, only once ?
>
> I don't think so.
>
> pc gets incremented at the bottom of the loop:
>
> pc += sizeof(int);
>
> Adjusting pc is necessary at each iteration. Leaving this block inside
> the loop seems correct.

This looks pretty strange.
The first time, pc is a physical address, that you change to a virtual
address. Then when you increment it it is still a virtual address.
So when you call phys_to_virt(pc) for the second time, pc is already a
virt address, so what happens indeed ?

Christophe

>
> Cheers
> Murilo
>

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