linux-kernel - Re: linux-next: build failure after merge of the modules tree

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Date:   Wed, 10 Feb 2021 09:06:48 +0100
From:   Jessica Yu <jeyu@...nel.org>
To:     Stephen Rothwell <sfr@...b.auug.org.au>
Cc:     Christoph Hellwig <hch@....de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Masahiro Yamada <masahiroy@...nel.org>
Subject: Re: linux-next: build failure after merge of the modules tree

+++ Stephen Rothwell [10/02/21 08:50 +1100]:
>Hi Jessica,
>
>On Tue, 9 Feb 2021 16:16:20 +0100 Jessica Yu <jeyu@...nel.org> wrote:
>>
>> Hmm, these errors don't look like it's related to that particular commit. I was
>
>I found this commit by bisection and then tested by reverting it.
>
>Before this commit, CONFIG_TRIM_UNUSED_KSYMS would not be set in the
>allyesconfig build because CONFIG_UNUSED_SYMBOLS was set.  After this
>commit, CONFIG_TRIM_UNUSED_KSYMS will be set in the allyesconfig build.

Ah, that makes sense then. I would get the error on powerpc whenever
CONFIG_TRIM_UNUSED_KSYMS was enabled.

>> able to reproduce these weird autoksym errors even without any modules-next
>> patches applied, and on a clean v5.11-rc7 tree. To reproduce it,
>> CONFIG_TRIM_UNUSED_KSYMS needs to be enabled. I guess that's why we run into
>> these errors with allyesconfig. I used a gcc-7 ppc64le cross compiler and got
>> the same compiler warnings. It seems to not compile on powerpc properly because
>> it looks like some symbols have an extra dot "." prefix, for example in
>> kthread.o:
>>
>>     168: 0000000000000318    24 NOTYPE  GLOBAL DEFAULT    6 kthread_create_worker
>>     169: 0000000000001d90   104 FUNC    GLOBAL DEFAULT    1 .kthread_create_worker
>>     170: 0000000000000330    24 NOTYPE  GLOBAL DEFAULT    6 kthread_create_worker_on_cpu
>>     171: 0000000000001e00    88 FUNC    GLOBAL DEFAULT    1 .kthread_create_worker_on_cpu
>>     172: 0000000000000348    24 NOTYPE  GLOBAL DEFAULT    6 kthread_queue_work
>>     173: 0000000000001e60   228 FUNC    GLOBAL DEFAULT    1 .kthread_queue_work
>>
>> So I suppose this dot prefix is specific to powerpc. From the ppc64 elf abi docs:
>>
>>      Symbol names with a dot (.) prefix are reserved for holding entry point
>>      addresses. The value of a symbol named ".FN", if it exists, is the entry point
>>      of the function "FN".
>>
>> I guess the presence of the extra dot symbols is confusing
>> scripts/gen_autoksyms.sh, so we get the dot symbols in autoksyms.h, which the
>> preprocessor doesn't like. I am wondering how this was never caught until now
>> and also now curious if this feature was ever functional on powerpc..
>
>Which feature?

Sorry, by "feature" I meant CONFIG_TRIM_UNUSED_KSYMS. This config
option was introduced around v4.7. If simply enabling it produces
these compilation errors I was wondering if it ever built properly on
powerpc.

Thanks,

Jessica