linux-kernel - Re: [PATCH 6/6] selftests/sgx: Add a bpftrace script for tracking allocation errors

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Date:   Thu, 1 Sep 2022 15:34:49 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>
Cc:     linux-sgx@...r.kernel.org,
        Haitao Huang <haitao.huang@...ux.intel.com>,
        Vijay Dhanraj <vijay.dhanraj@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Shuah Khan <shuah@...nel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH 6/6] selftests/sgx: Add a bpftrace script for tracking
 allocation errors

On 9/1/22 15:20, Jarkko Sakkinen wrote:
>>> +kr:sgx_alloc_epc_page /(uint64)retval >= (uint64)(-4095)/ {
>>> +		 printf("sgx_alloc_epc_page: retval=%d\n", (int64)retval);
>>> +}
>>> +
>>> +kr:sgx_encl_page_alloc /(uint64)retval >= (uint64)(-4095)/ {
>>> +		 printf("sgx_encl_page_alloc: retval=%d\n", (int64)retval);
>>> +}
>> I guess this doesn't _hurt_, but it's also not exactly the easiest way
>> to get this done.  You need a whole bpf toolchain.  You could also just do:
>>
>> 	perf probe 'sgx_encl_page_alloc%return $retval'
>>
>> Even *that* can be replicated in a few scant lines of shell code echoing
>> into /sys/kernel/debug/tracing.
> Thanks, I have not used perf that much. What if I replace
> this with a shell script using perf? How do you use that
> for two kretprobes?

The manpage is pretty good.

But, I'd proably be doing something along these lines:

	perf probe 'sgx_encl_page_alloc%return ret=$retval'
	perf record -e probe:sgx_encl_page_alloc -aR	\
		--filter='ret >= 0xwhatever' sleep 1
	perf script

There are probably shorter ways to do it, but I'm pretty sure that works.