linux-kernel - Re: [PATCH 2/2] ARM: mm: hide __start_rodata_section

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Date:	Tue, 16 Feb 2016 17:36:33 +0100
From:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Russell King <linux@....linux.org.uk>,
	Kees Cook <keescook@...omium.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Chris Brandt <chris.brandt@...esas.com>,
	Laura Abbott <labbott@...oraproject.org>
Subject: Re: [PATCH 2/2] ARM: mm: hide __start_rodata_section_aligned for
 non-debug builds

On 16 February 2016 at 17:34, Arnd Bergmann <arnd@...db.de> wrote:
> On Tuesday 16 February 2016 17:12:52 Ard Biesheuvel wrote:
>> > +#ifdef CONFIG_DEBUG_RODATA
>> >  /*
>> >   * Without CONFIG_DEBUG_ALIGN_RODATA, __start_rodata_section_aligned will
>> >   * be the first section-aligned location after __start_rodata. Otherwise,
>> >   * it will be equal to __start_rodata.
>> >   */
>> >  __start_rodata_section_aligned = ALIGN(__start_rodata, 1 << SECTION_SHIFT);
>> > +#endif
>> >
>>
>> Does
>>
>> PROVIDE(__start_rodata_section_aligned = xxx);
>>
>> do the trick as well? If it does, it's a bit cleaner.
>>
>
> I would assume not, as the problem is that SECTION_SHIFT is a macro that
> is not defined when the MMU is disabled.
>

I just tested it myself, and it in fact does work.

PROVIDE() means the expression is evaluated lazily, and SECTION_SHIFT
is just an undefined identifier in the linker script scope if the
preprocessor does not define it.

Anyway, I don't have a strong preference, so ack either way.