linux-kernel - Re: [PATCH v2 0/6] macros for section name cleanup

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Message-ID: <20090504175427.GB9489@uranus.ravnborg.org>
Date:	Mon, 4 May 2009 19:54:27 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Mike Frysinger <vapier.adi@...il.com>
Cc:	Tim Abbott <tabbott@....edu>,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>,
	linux arch <linux-arch@...r.kernel.org>,
	Anders Kaseorg <andersk@....edu>
Subject: Re: [PATCH v2 0/6] macros for section name cleanup

On Mon, May 04, 2009 at 01:42:08PM -0400, Mike Frysinger wrote:
> On Mon, May 4, 2009 at 12:32, Tim Abbott wrote:
> > On Mon, 4 May 2009, Sam Ravnborg wrote:
> >> +#define RW_DATA_SECTION(page_align, readmostly_align, cache_align,
> >>   inittask_align) \
> >> +     . = ALIGN(PAGE_SIZE);                                           \
> >> +     .data : AT(ADDR(.data) - LOAD_OFFSET) {                         \
> >> +             DATA_DATA                                               \
> >> +             CONSTRUCTORS                                            \
> >> +             NOSAVE_DATA                                             \
> >> +             PAGE_ALIGNED_DATA(page_align)                           \
> >> +             READMOSTLY_DATA(readmostly_align)                       \
> >> +             CACHELINE_ALIGNED_DATA(cache_align)                     \
> >> +             INIT_TASK(inittask_align)                               \
> >> +     }
> >
> > How did you pick the order of the sections here?  I would think that to
> > pack the .data section efficiently, you'd want to sort by alignment
> > requirements so that e.g. all the at-least-page aligned sections are
> > adjacent (INIT_TASK and the page-aligned sections are separated by some
> > much smaller aligments here).
> 
> if this were actually the case, there should of course be some /*
> comments */ above the define explaining that the order wasnt
> arbitrarily pulled like a rabbit from an orifice.  if you're
> scratching your head, then there's going to be plenty more people who
> never ask but treat it like untouchable voodoo.

Point taken (from both of you).
I will try to document the order in next version.

In reality I just picked the order used for 32 bit x86 IIRC.

	Sam
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