linux-kernel - Re: [PATCH 5/8] trace_uprobe: Support SDT markers having reference count (semaphore)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <fabfad9d-a75e-0b18-1558-ce738b46e538@linux.vnet.ibm.com>
Date:   Wed, 14 Mar 2018 20:42:24 +0530
From:   Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     oleg@...hat.com, peterz@...radead.org, srikar@...ux.vnet.ibm.com,
        acme@...nel.org, ananth@...ux.vnet.ibm.com,
        akpm@...ux-foundation.org, alexander.shishkin@...ux.intel.com,
        alexis.berlemont@...il.com, corbet@....net,
        dan.j.williams@...el.com, gregkh@...uxfoundation.org,
        huawei.libin@...wei.com, hughd@...gle.com, jack@...e.cz,
        jglisse@...hat.com, jolsa@...hat.com, kan.liang@...el.com,
        kirill.shutemov@...ux.intel.com, kjlx@...pleofstupid.com,
        kstewart@...uxfoundation.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org, mhocko@...e.com,
        milian.wolff@...b.com, mingo@...hat.com, namhyung@...nel.org,
        naveen.n.rao@...ux.vnet.ibm.com, pc@...ibm.com,
        pombredanne@...b.com, rostedt@...dmis.org, tglx@...utronix.de,
        tmricht@...ux.vnet.ibm.com, willy@...radead.org,
        yao.jin@...ux.intel.com, fengguang.wu@...el.com,
        Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Subject: Re: [PATCH 5/8] trace_uprobe: Support SDT markers having reference
 count (semaphore)

Hi Masami,

On 03/14/2018 07:18 PM, Masami Hiramatsu wrote:
> Hi Ravi,
>
> On Tue, 13 Mar 2018 18:26:00 +0530
> Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com> wrote:
>
>> Userspace Statically Defined Tracepoints[1] are dtrace style markers
>> inside userspace applications. These markers are added by developer at
>> important places in the code. Each marker source expands to a single
>> nop instruction in the compiled code but there may be additional
>> overhead for computing the marker arguments which expands to couple of
>> instructions. In case the overhead is more, execution of it can be
>> ommited by runtime if() condition when no one is tracing on the marker:
>>
>>     if (reference_counter > 0) {
>>         Execute marker instructions;
>>     }
>>
>> Default value of reference counter is 0. Tracer has to increment the
>> reference counter before tracing on a marker and decrement it when
>> done with the tracing.
>>
>> Implement the reference counter logic in trace_uprobe, leaving core
>> uprobe infrastructure as is, except one new callback from uprobe_mmap()
>> to trace_uprobe.
>>
>> trace_uprobe definition with reference counter will now be:
>>
>>   <path>:<offset>[(ref_ctr_offset)]
> Would you mean 
> <path>:<offset>(<ref_ctr_offset>)
> ?
>
> or use "[]" for delimiter?

[] indicates optional field.

> Since,
>
>> @@ -454,6 +458,26 @@ static int create_trace_uprobe(int argc, char **argv)
>>  		goto fail_address_parse;
>>  	}
>>  
>> +	/* Parse reference counter offset if specified. */
>> +	rctr = strchr(arg, '(');
> This seems you choose "()" for delimiter.

Correct.

>> +	if (rctr) {
>> +		rctr_end = strchr(arg, ')');
> 		rctr_end = strchr(rctr, ')');
>
> ? since we are sure rctr != NULL.

Yes. we can use rctr instead of arg.

>> +		if (rctr > rctr_end || *(rctr_end + 1) != 0) {
>> +			ret = -EINVAL;
>> +			pr_info("Invalid reference counter offset.\n");
>> +			goto fail_address_parse;
>> +		}
>
> Also
>
>> +
>> +		*rctr++ = 0;
>> +		*rctr_end = 0;
> Please consider to use '\0' for nul;

Sure. Will change it.

Thanks for the review :)
Ravi