Subject: [PATCH v2] ARM: unwinder: Fix handling of 'fp' in thumb2 mode

From: [email-masked] (Nikolay Borisov)
Date: Tue, 6 May 2014 10:02:02 +0100

Hi, 
> -----Original Message-----
> From: Anurag Aggarwal [mailto:anurag19aggarwal at gmail.com]
> Sent: 03 May 2014 07:57
> To: Nikolay Borisov
> Cc: linux-arm-kernel at lists.infradead.org; Dave P Martin; Catalin
> Marinas
> Subject: Re: [PATCH v2] ARM: unwinder: Fix handling of 'fp' in thumb2
> mode
> 
> Seems good.
> 
> I would like to know what kind of testing you have done that for this,
> Other than that you can add my review statement
>

Without this patch if you use the magic sysrq to print backtrace of all
the running tasks in the system those that are sleeping would not print 
a backtrace. With the patch this works correctly. Another case where you
can observe the change is in the invocation of the "ps -Al" which shows
(among other things) which function the sleeping task is blocked in. 

> On Fri, May 2, 2014 at 9:07 PM, Nikolay Borisov
> <[email-masked]> wrote:
> > The thread_save_fp macro has been defined so that it always reads the
> fp member
> > of the cpu_context_save struct. However, in the case of THUMB2 the fp
> is saved
> > not in the fp (r11) member but rather in r7.
> >
> > This patch changes the way the macro is defined such that FP is read
> from the
> > correct place depending on whether we are a THUMB2 kernel or not.
> This enables
> > the backtrace in sitaution such as "echo t > /proc/sysrq-trigger" or
> the
> > function in which a process sleeping when "ps -Al" is invoked.
> >
> > Another place where similar change is requried is when working with
> pt_reg.
> > regs->ARM_fp is defined such that r11 is always referenced as the
> frame pointer,
> > so the definition of ARM_fp needs to change depending on the type of
> kernel we
> > are running.
> >
> > Changes since v1:
> > * Added changes for the pt_reg structure.
> >
> > Signed-off-by: Nikolay Borisov <[email-masked]>
> 
> Reviewed-by: Anurag Aggarwal <[email-masked]>
> 
> >
> > handle the case when we've got regs present
> > ---
> >  arch/arm/include/asm/thread_info.h | 6 ++++++
> >  arch/arm/include/uapi/asm/ptrace.h | 4 ++++
> >  2 files changed, 10 insertions(+)
> >
> > diff --git a/arch/arm/include/asm/thread_info.h
> b/arch/arm/include/asm/thread_info.h
> > index f989d7c..e4e4208 100644
> > --- a/arch/arm/include/asm/thread_info.h
> > +++ b/arch/arm/include/asm/thread_info.h
> > @@ -114,8 +114,14 @@ static inline struct thread_info
> *current_thread_info(void)
> >         ((unsigned long)(task_thread_info(tsk)->cpu_context.pc))
> >  #define thread_saved_sp(tsk)   \
> >         ((unsigned long)(task_thread_info(tsk)->cpu_context.sp))
> > +
> > +#ifndef CONFIG_THUMB2_KERNEL
> >  #define thread_saved_fp(tsk)   \
> >         ((unsigned long)(task_thread_info(tsk)->cpu_context.fp))
> > +#else
> > +#define thread_saved_fp(tsk)   \
> > +       ((unsigned long)(task_thread_info(tsk)->cpu_context.r7))
> > +#endif
> >
> >  extern void crunch_task_disable(struct thread_info *);
> >  extern void crunch_task_copy(struct thread_info *, void *);
> > diff --git a/arch/arm/include/uapi/asm/ptrace.h
> b/arch/arm/include/uapi/asm/ptrace.h
> > index 5af0ed1..92e1bae 100644
> > --- a/arch/arm/include/uapi/asm/ptrace.h
> > +++ b/arch/arm/include/uapi/asm/ptrace.h
> > @@ -131,7 +131,11 @@ struct pt_regs {
> >  #define ARM_lr         uregs[14]
> >  #define ARM_sp         uregs[13]
> >  #define ARM_ip         uregs[12]
> > +#ifndef CONFIG_THUMB2_KERNEL
> >  #define ARM_fp         uregs[11]
> > +#else
> > +#define ARM_fp         uregs[7]
> > +#endif
> >  #define ARM_r10                uregs[10]
> >  #define ARM_r9         uregs[9]
> >  #define ARM_r8         uregs[8]
> > --
> > 1.8.1.5
> >
> >