linux-kernel - Re: linux-next: build warnings after merge of the kbuild tree

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Date:   Sat, 2 Jun 2018 22:39:20 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Kees Cook <keescook@...omium.org>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: linux-next: build warnings after merge of the kbuild tree

On Fri, Jun 1, 2018 at 6:01 AM, Kees Cook <keescook@...omium.org> wrote:
> On Thu, May 31, 2018 at 6:56 PM, Masahiro Yamada
> <yamada.masahiro@...ionext.com> wrote:
>> 2018-05-31 12:53 GMT+09:00 Kees Cook <keescook@...omium.org>:
>>> On Wed, May 30, 2018 at 6:26 PM, Kees Cook <keescook@...omium.org> wrote:
>>>> On Wed, May 30, 2018 at 6:12 PM, Masahiro Yamada

>>>>> This has been triggered by the following commit:
>>>>>
>>>>>
>>>>> commit 0e461945f3504e09b8ecf947b6398adce1287a28
>>>>> Author: Masahiro Yamada <yamada.masahiro@...ionext.com>
>>>>> Date:   Mon May 28 18:22:07 2018 +0900
>>>>>
>>>>>     gcc-plugins: allow to enable GCC_PLUGINS for COMPILE_TEST
>>>>>
>>>>>
>>>>>
>>>>> CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL was previously disabled
>>>>> for COMPILE_TEST, which is now enabled.
>
> For the moment, can you add "depends on !COMPILE_TEST" to
> CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL in your tree and I'll continue
> to figure out what's happening?
>

I ran into the same thing indepently and bisected it (which led me to
arrive at this thread).
One additional bit of information I have is that this happens with all
versions of
gcc-7 for me, but not gcc-6.3 or older.

Another finding was the particular instance I noticed:

fs/ext4/inode.c: In function 'ext4_inode_csum':
fs/ext4/inode.c:83:1: warning: the frame size of 1688 bytes is larger
than 500 bytes [-Wframe-larger-than=]

comes from inlining the same function multiple times; ext4_inode_csum()
repeatedly calls ext4_chksum(), which has a struct on the stack. Apparently
this normally only takes up stack space only once, but when initializing it
to zero, each instance takes an additional two CRYPTO_MINALIGN bytes
of stack space (the size of the locally defined structure).


       Arnd