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SubjectRe: [PATCH v4 5/6] powerpc: Add show_user_instructions()
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.

> > +
> > + 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.

Cheers
Murilo

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