linux-kernel - Re: [GIT PULL] kbuild changes for v4.9-rc1

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Date:   Sun, 18 Dec 2016 16:08:10 +0100
From:   Jiri Slaby <jslaby@...e.cz>
To:     Nikolay Borisov <n.borisov.lkml@...il.com>,
        Arend Van Spriel <arend.vanspriel@...adcom.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Adam Borowski <kilobyte@...band.pl>,
        Nicholas Piggin <npiggin@...il.com>,
        Omar Sandoval <osandov@...ndov.com>,
        Michal Marek <mmarek@...e.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: Re: [GIT PULL] kbuild changes for v4.9-rc1

On 12/18/2016, 03:54 PM, Nikolay Borisov wrote:
> 
> 
> On 18.12.2016 16:45, Jiri Slaby wrote:
>> Moreover, with some modules, __put_user_1 and others are reported
>> instead of mcount.
> 
> 
> nm vmlinux | grep __fentry__
> nm vmlinux | grep mcount
> 
> What do these report ? I bet you that in your vmlinux the first one
> would return something like :
> 
> ffffffff822f1810 T __fentry__
> ffffffff827fdc20 r __kcrctab___fentry__
> ffffffff82809461 r __kstrtab___fentry__
> ffffffff827e6c20 R __ksymtab___fentry__
>  and nothing for the second. Whereas doing nm on the module in question
> would give nothing for __fentry__ and something like: U mcount

Well, I have just won a beer:
$ nm vmlinux | grep mcount
         w __crc_mcount
c0b3bd34 r __kcrctab_mcount
c0b41692 r __kstrtab_mcount
c0b2dd04 R __ksymtab_mcount
c0896130 T mcount
c0c9ee20 T __start_mcount_loc
c0cba89c T __stop_mcount_loc
$ nm vmlinux | grep __fentry__
$ nm sound/soundcore.ko | grep mcount
         U mcount

No, I am really not stupid. We compile the kernels like this for over a
decade and it really broke with 4.9. Applying the patch fixes the
problem. Reverting it, makes it recur.

regards,
-- 
js
suse labs