linux-kernel - Re: [PATCH v7 02/10] module: allow symbol exports to be disabled

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Date:   Tue, 2 Jan 2018 23:55:05 +0000
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Nicolas Pitre <nicolas.pitre@...aro.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Arnd Bergmann <arnd@...db.de>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Kees Cook <keescook@...omium.org>,
        Will Deacon <will.deacon@....com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Thomas Garnier <thgarnie@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Russell King <linux@...linux.org.uk>,
        Paul Mackerras <paulus@...ba.org>,
        Catalin Marinas <catalin.marinas@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Petr Mladek <pmladek@...e.com>, Ingo Molnar <mingo@...hat.com>,
        James Morris <james.l.morris@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jessica Yu <jeyu@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-mips <linux-mips@...ux-mips.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        sparclinux@...r.kernel.org,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Matt Fleming <matt@...eblueprint.co.uk>
Subject: Re: [PATCH v7 02/10] module: allow symbol exports to be disabled

On 2 January 2018 at 23:47, Nicolas Pitre <nicolas.pitre@...aro.org> wrote:
> On Tue, 2 Jan 2018, Ard Biesheuvel wrote:
>
>> To allow existing C code to be incorporated into the decompressor or
>> the UEFI stub, introduce a CPP macro that turns all EXPORT_SYMBOL_xxx
>> declarations into nops, and #define it in places where such exports
>> are undesirable. Note that this gets rid of a rather dodgy redefine
>> of linux/export.h's header guard.
> [...]
>
>> --- a/include/linux/export.h
>> +++ b/include/linux/export.h
>> @@ -83,6 +83,15 @@ extern struct module __this_module;
>>   */
>>  #define __EXPORT_SYMBOL(sym, sec)    === __KSYM_##sym ===
>>
>> +#elif defined(__DISABLE_EXPORTS)
>> +
>> +/*
>> + * Allow symbol exports to be disabled completely so that C code may
>> + * be reused in other execution contexts such as the UEFI stub or the
>> + * decompressor.
>> + */
>> +#define __EXPORT_SYMBOL(sym, sec)
>> +
>
> I think you should rather put this first thing in the #if sequence so to
> override the defined(__KSYM_DEPS__) case too.  No need to create build
> dependencies for module symbols that you're going to stub out
> afterwards anyway.
>

I wasn't sure, so thanks for clearing that up.