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From: Isaac Dunham <ibid.ag@gmail.com>
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Subject: Re: Why musl define PAGE_SIZE
Date: Fri, 11 Sep 2015 12:44:02 -0700
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On Fri, Sep 11, 2015 at 03:28:52PM -0400, Yuxin Ren wrote:
> Hi,
> 
> I found in the bits/limits.h file, musl defines PAGE_SIZE macro .
> I think this macro is always defined by operating system, not libc.
> 
> Why does musl define this marco?

It's required to be in limits.h, which has to be provided by libc for a
full implementation.
Hypothetically, we could get it from the Linux headers.
But the Linux headers can and sometimes do introduce definitions and
structs that violate the header namespaces, resulting in collisions
(ie, kernel header defines struct foo, application defines struct foo
without including any headers that *should* define it, application fails
to compile.)

HTH,
Isaac Dunham