linux-kernel - Re: [PATCH v7 18/43] instrumented.h: add KMSAN support

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Date:   Fri, 21 Oct 2022 10:21:12 -0700
From:   Kees Cook <kees@...nel.org>
To:     Alexander Potapenko <glider@...gle.com>,
        youling 257 <youling257@...il.com>
CC:     Marco Elver <elver@...gle.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Christoph Hellwig <hch@....de>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Eric Biggers <ebiggers@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Ingo Molnar <mingo@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Kees Cook <keescook@...omium.org>,
        Mark Rutland <mark.rutland@....com>,
        Matthew Wilcox <willy@...radead.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Pekka Enberg <penberg@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Petr Mladek <pmladek@...e.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Vegard Nossum <vegard.nossum@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, kasan-dev@...glegroups.com,
        linux-mm@...ck.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 18/43] instrumented.h: add KMSAN support

On October 21, 2022 10:02:05 AM PDT, Alexander Potapenko <glider@...gle.com> wrote:
>On Fri, Oct 21, 2022 at 8:19 AM youling 257 <youling257@...il.com> wrote:
>
>> CONFIG_DEBUG_INFO=y
>> CONFIG_AS_HAS_NON_CONST_LEB128=y
>> # CONFIG_DEBUG_INFO_NONE is not set
>> CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
>> # CONFIG_DEBUG_INFO_DWARF4 is not set
>> # CONFIG_DEBUG_INFO_DWARF5 is not set
>> # CONFIG_DEBUG_INFO_REDUCED is not set
>> # CONFIG_DEBUG_INFO_COMPRESSED is not set
>> # CONFIG_DEBUG_INFO_SPLIT is not set
>> # CONFIG_DEBUG_INFO_BTF is not set
>> # CONFIG_GDB_SCRIPTS is not set
>>
>> perf top still no function name.
>>
>Will it help if you disable CONFIG_RANDOMIZE_BASE?
>(if it doesn't show the symbols, at least we'll be able to figure out the
>offending function by running nm)

Is KALLSYMS needed?

>
>
>>
>> 12.90%  [kernel]              [k] 0xffffffff833dfa64
>>      3.78%  [kernel]              [k] 0xffffffff8285b439
>>      3.61%  [kernel]              [k] 0xffffffff83370254
>>      2.32%  [kernel]              [k] 0xffffffff8337025b
>>      1.88%  bluetooth.default.so  [.] 0x000000000000d09d
>>
>> 2022-10-21 15:37 GMT+08:00, Marco Elver <elver@...gle.com>:
>> > On Thu, 20 Oct 2022 at 23:39, youling 257 <youling257@...il.com> wrote:
>> >>
>> >> PerfTop:    8253 irqs/sec  kernel:75.3%  exact: 100.0% lost: 0/0 drop:
>> >> 0/17899 [4000Hz cycles],  (all, 8 CPUs)
>> >>
>> ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>> >>
>> >>     14.87%  [kernel]              [k] 0xffffffff941d1f37
>> >>      6.71%  [kernel]              [k] 0xffffffff942016cf
>> >>
>> >> what is 0xffffffff941d1f37?
>> >
>> > You need to build with debug symbols:
>> > CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
>> >
>> > Then it'll show function names.
>> >
>> >> 2022-10-21 14:16 GMT+08:00, Marco Elver <elver@...gle.com>:
>> >> > On Thu, 20 Oct 2022 at 22:55, youling 257 <youling257@...il.com>
>> wrote:
>> >> >>
>> >> >> How to use perf tool?
>> >> >
>> >> > The simplest would be to try just "perf top" - and see which kernel
>> >> > functions consume most CPU cycles. I would suggest you compare both
>> >> > kernels, and see if you can spot a function which uses more cycles% in
>> >> > the problematic kernel.
>> >> >
>> >
>>
>
>


-- 
Kees Cook