linux-kernel - Re: [PATCH] ARM: Print BUG instead of undefined instruction on BUG

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Message-ID: <CAPnjgZ2LGjMM7QwoJrf2==3th4cT+s75ebV9q+eXudF4o5E_pA@mail.gmail.com>
Date:	Tue, 17 Jan 2012 12:04:11 -0800
From:	Simon Glass <sjg@...omium.org>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: Print BUG instead of undefined instruction on BUG_ON()

On Mon, Jan 16, 2012 at 9:07 AM, Stephen Boyd <sboyd@...eaurora.org> wrote:
> The ARM kernel uses undefined instructions to implement
> BUG/BUG_ON(). This leads to problems where people don't read one
> line above the Oops message and see the "kernel BUG at ..."
> message and so they wrongly assume the kernel has hit an
> undefined instruction.
>
> Instead of printing:
>
>  Internal error: Oops - undefined instruction: 0 [#1] PREEMPT SMP
>
> print
>
>  Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
>
> This should prevent people from thinking the BUG_ON was an
> undefined instruction when it was actually intentional.
>
> Cc: Simon Glass <sjg@...omium.org>
> Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>

Tested on a Tegra20 system. I would like to adjust the backtrace
output slightly so will send a patch for that at the same time, since
we are in there.

Acked-by: Simon Glass <sjg@...omium.org>
Tested-by: Simon Glass <sjg@...omium.org>

> ---
>  arch/arm/kernel/traps.c |    5 ++++-
>  1 files changed, 4 insertions(+), 1 deletions(-)
>
> diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
> index 99a5727..f84dfe6 100644
> --- a/arch/arm/kernel/traps.c
> +++ b/arch/arm/kernel/traps.c
> @@ -266,6 +266,7 @@ void die(const char *str, struct pt_regs *regs, int err)
>  {
>        struct thread_info *thread = current_thread_info();
>        int ret;
> +       enum bug_trap_type bug_type = BUG_TRAP_TYPE_NONE;
>
>        oops_enter();
>
> @@ -273,7 +274,9 @@ void die(const char *str, struct pt_regs *regs, int err)
>        console_verbose();
>        bust_spinlocks(1);
>        if (!user_mode(regs))
> -               report_bug(regs->ARM_pc, regs);
> +               bug_type = report_bug(regs->ARM_pc, regs);
> +       if (bug_type != BUG_TRAP_TYPE_NONE)
> +               str = "Oops - BUG";
>        ret = __die(str, err, thread, regs);
>
>        if (regs && kexec_should_crash(thread->task))
> --
> Sent by an employee of the Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
>
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