Re: [PATCH 2/2] MIPS: get schedule_mfi info from __schedule

[Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>]

Hello.

On 09-05-2013 18:49, Tony Wu wrote:

> schedule_mfi is supposed to be extracted from schedule(), and
> is used in thread_saved_pc and get_wchan.

> But, after optimization, schedule() is reduced to a sibling
> call to __schedule(), and no real frame info can be extracted.

> One solution is to compile schedule() with -fno-omit-frame-pointer
> and -fno-optimize-sibling-calls, but that will incur performance
> degradation.

> This patch follows the sibling call and extracts the
> schedule_mfi from the __schedule with and without KALLSYMS enabled.

> Signed-off-by: Tony Wu <tung7970@gmail.com>
> ---
>   arch/mips/kernel/process.c |   28 ++++++++++++++++++++++++++--
>   1 file changed, 26 insertions(+), 2 deletions(-)

> diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
> index a794eb5..289ea69 100644
> --- a/arch/mips/kernel/process.c
> +++ b/arch/mips/kernel/process.c
> @@ -314,15 +314,39 @@ err:
>
>   static struct mips_frame_info schedule_mfi __read_mostly;
>
> +static unsigned long get___schedule_addr(void)
> +{
> +#ifdef CONFIG_KALLSYMS
> +	return kallsyms_lookup_name("__schedule");
> +#else
> +	union mips_instruction *ip = (void *)schedule;
> +	int max_insns = 8;
> +	int i;
> +
> +	for (i = 0; i < max_insns; i++, ip++) {
> +		if (ip->j_format.opcode == j_op)
> +			return J_TARGET(ip, ip->j_format.target);
> +	}
> +	return 0;
> +#endif
> +}
> +

     #ifdef's inside function body are frowned upon. Better code it as:

#ifdef CONFIG_KALLSYMS
static unsigned long get___schedule_addr(void)
{
	return kallsyms_lookup_name("__schedule");
}
#else
static unsigned long get___schedule_addr(void)
{
	union mips_instruction *ip = (void *)schedule;
[...]
	return 0;
}
#endif

WBR, Sergei