linux-kernel - Re: [PATCH v3 2/3] Support for perf to probe into SDT markers:

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Message-ID: <52638B44.2030800@linux.vnet.ibm.com>
Date:	Sun, 20 Oct 2013 13:20:28 +0530
From:	Hemant Kumar <hkshaw@...ux.vnet.ibm.com>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
CC:	linux-kernel@...r.kernel.org, srikar@...ux.vnet.ibm.com,
	peterz@...radead.org, oleg@...hat.com,
	hegdevasant@...ux.vnet.ibm.com, mingo@...hat.com, anton@...hat.com,
	systemtap@...rceware.org, namhyung@...nel.org,
	aravinda@...ux.vnet.ibm.com
Subject: Re: [PATCH v3 2/3] Support for perf to probe into SDT markers:

On 10/19/2013 09:18 PM, Masami Hiramatsu wrote:
> [...]
> +
> +	/*
> +	 * Find out the .stapsdt.base section.
> +	 * This scn will help us to handle prelinking (if present).
> +	 * Compare the retrieved file offset of the base section with the
> +	 * base address in the description of the SDT note. If its different,
> +	 * then accordingly, adjust the note location.
> +	 */
> +	if (elf_section_by_name(elf, &ehdr, &shdr, SDT_BASE_SCN, NULL))
> +		base_off = shdr.sh_offset;
> +	if (base_off) {
> +		if (tmp->bit32)
> +			key->addr.a32[0] = tmp->addr.a32[0] + base_off -
> +				tmp->addr.a32[1];
> +		else
> +			key->addr.a64[0] = tmp->addr.a64[0] + base_off -
> +				tmp->addr.a64[1];
> +	}
> +	key->bit32 = tmp->bit32;
> +}
> +
> +int search_sdt_note(struct sdt_note *key, struct list_head *sdt_notes,
> +		    const char *target)
> Hmm, this interface looks very odd.
>   - This just finds the first matched sdt_note entry instead of the list.
>     In that case, we don't need to pass the list_head.
>   - If the purpose is just counting the number of matched entries (or just
>     checking existence), we also don't need the list. Just returning the
>     number is enough.
>
> I recommend you to remove the "sdt_notes", and make the caller check
> key->addr is set.

Yeah, list isn't required in this case. Thanks for pointing that out. 
Will change that.

> [...]
>
-- 
Thanks
Hemant Kumar

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