Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Sinan Kaya <Okaya@kernel.org>
Subject: Re: [PATCH v3] init: Do not select DEBUG_KERNEL by default
To:     Masahiro Yamada <yamada.masahiro@socionext.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Josh Triplett <josh@joshtriplett.org>,
        Kees Cook <keescook@chromium.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Adrian Reber <adrian@lisas.de>,
        Richard Guy Briggs <rgb@redhat.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Petr Mladek <pmladek@suse.com>,
        Joe Lawrence <joe.lawrence@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Mikulas Patocka <mpatocka@redhat.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        Changbin Du <changbin.du@intel.com>
References: <20190411005634.8495-1-okaya@kernel.org>
 <CAK7LNAS=G7-nXr=pT2EYExGNkCcOcd2NH1haaBMt+JsyhX2Z8Q@mail.gmail.com>
 <c8babeca-2d24-4265-0477-0634d87efa70@kernel.org>
 <CAK7LNARB54R5OfADaxzO=Mu8LucCd7wPVS4Yys8cfCKUpYc6Cg@mail.gmail.com>
Message-ID: <ac79dcfc-50cc-01d4-758c-8c0881ab0d2e@kernel.org>
Date:   Thu, 11 Apr 2019 14:15:36 -0400
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101
 Thunderbird/60.6.1
MIME-Version: 1.0
In-Reply-To: <CAK7LNARB54R5OfADaxzO=Mu8LucCd7wPVS4Yys8cfCKUpYc6Cg@mail.gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 4/11/2019 1:48 AM, Masahiro Yamada wrote:
>> I was going by what Kconfig tells me
>>
>> Symbol: KALLSYMS_ALL [=n]
>>    Depends on: DEBUG_KERNEL [=n] && KALLSYMS [=y]
> Lots of features have 'depends on DEBUG_KERNEL'.
> What is special about KALLSYMS_ALL here?

I had to do some learning about KALLSYSM_ALL. Based on my limited
searching, KALLSYMS_ALL allows you to locate the symbol location
at runtime from the kernel.

Without KALLSYM_ALL, you can only locate the kernel code only. With
KALLSYMS_ALL, you can locate the symbols for any data structure
including kernel modules.

I'm not a KALLSYMS person but based on my search, I'd consider
KALLSYMS_ALL a debug feature as it is today.

kernel/kallsyms.c:              else if (IS_ENABLED(CONFIG_KALLSYMS_ALL))
kernel/livepatch/Kconfig:       depends on KALLSYMS_ALL
kernel/module.c:#ifdef CONFIG_KALLSYMS_ALL
kernel/module.c:#ifndef CONFIG_KALLSYMS_ALL

lib/Kconfig.debug:      select KALLSYMS_ALL
     config LOCKDEP
             bool
             depends on DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT
             select KALLSYMS
             select KALLSYMS_ALL

lib/Kconfig.debug:      select KALLSYMS_ALL
     config LATENCYTOP
             bool "Latency measuring infrastructure"
             select KALLSYMS
             select KALLSYMS_ALL

scripts/link-vmlinux.sh:        if [ -n "${CONFIG_KALLSYMS_ALL}" ]; then