linux-kernel - Re: [PATCH v2 09/13] ARM: Disable jprobe selftests in thumb kernels

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Date:	Sun, 10 Nov 2013 17:57:06 -0500
From:	David Long <dave.long@...aro.org>
To:	"Jon Medhurst (Tixy)" <tixy@...aro.org>
CC:	linux-arm-kernel@...ts.infradead.org, Rabin Vincent <rabin@....in>,
	Oleg Nesterov <oleg@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Dave Martin <dave.martin@...aro.org>
Subject: Re: [PATCH v2 09/13] ARM: Disable jprobe selftests in thumb kernels

On 11/07/13 12:26, Jon Medhurst (Tixy) wrote:
> On Tue, 2013-10-15 at 17:04 -0400, David Long wrote:
>> From: "David A. Long" <dave.long@...aro.org>
>>
>> jprobe kernel selftests are not supported for thumb kernels. Conditionally
>> disable them in the kernel kprobes-test module.
>
> I don't think it's fair to say they aren't supported, it's just that the
> implementation of jprobes and/or symbol lookup has bugs on Thumb kernels
> which the test code is finding, see
> http://lists.infradead.org/pipermail/linux-arm-kernel/2011-August/063026.html
>
> Note, the current code works OK if the function being probed is in a
> loadable module (which is why I didn't spot the problem when doing the
> original Thumb kprobes work).
>
> Now I admit that having the tests always bombing out because of this
> hinders testing of kprobes, but simply disabling the test is just
> burying this long standing problem even more. So what do people think
> about something like the change below, to let other tests get run but
> make the overall test still fail...?
>
> --- a/arch/arm/kernel/kprobes-test.c
> +++ b/arch/arm/kernel/kprobes-test.c
> @@ -221,6 +221,7 @@ static int pre_handler_called;
>   static int post_handler_called;
>   static int jprobe_func_called;
>   static int kretprobe_handler_called;
> +static int tests_failed;
>
>   #define FUNC_ARG1 0x12345678
>   #define FUNC_ARG2 0xabcdef
> @@ -457,6 +458,13 @@ static int run_api_tests(long (*func)(long, long))
>
>   	pr_info("    jprobe\n");
>   	ret = test_jprobe(func);
> +#if defined(CONFIG_THUMB2_KERNEL) && !defined(MODULE)
> +	if (ret == -EINVAL) {
> +		pr_err("FAIL: Known longtime bug with jprobe on Thumb kernels");
> +		tests_failed = ret;
> +		ret = 0;
> +	}
> +#endif
>   	if (ret < 0)
>   		return ret;
>
> @@ -1667,6 +1675,8 @@ static int __init run_all_tests(void)
>
>   out:
>   	if (ret == 0)
> +		ret = tests_failed;
> +	if (ret == 0)
>   		pr_info("Finished kprobe tests OK\n");
>   	else
>   		pr_err("kprobe tests failed\n");
>
>
>
>


Thanks for clarifying the problem Tixy.  I agree we should try and allow 
the tests to run for these more typical use cases where they do actually 
work.  I have tested your patch and I will use it in place of mine 
unless there are strong objections.

-dl

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