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Re: [PATCH v2] [BZ #10283] localedef: align fixed maps to SHMLBA
- From: Roland McGrath <roland at hack dot frob dot com>
- To: "Carlos O'Donell" <carlos at redhat dot com>
- Cc: David Miller <davem at davemloft dot net>, vapier at gentoo dot org, libc-alpha at sourceware dot org
- Date: Tue, 28 May 2013 17:03:46 -0700 (PDT)
- Subject: Re: [PATCH v2] [BZ #10283] localedef: align fixed maps to SHMLBA
- References: <20130528194042 dot 1EF7B2C074 at topped-with-meat dot com> <20130528 dot 130721 dot 1721261559877509450 dot davem at davemloft dot net> <51A51186 dot 7070904 at redhat dot com> <20130528 dot 132601 dot 2200516495498570890 dot davem at davemloft dot net> <51A524FE dot 7040202 at redhat dot com> <20130528231403 dot 2C6C32C05D at topped-with-meat dot com> <51A544A5 dot 5050001 at redhat dot com>
> http://pubs.opengroup.org/onlinepubs/9699919799/functions/mmap.html
> ~~~
> If MAP_FIXED is specified, the implementation may
> require that addr is a multiple of the page size.
> ~~~
> Thus addr must be aligned to N*<page size>, where N is implementation
> specific.
I think you misread that. "addr is a multiple of the page size" means the
same as "addr is aligned to page size". The standard says that the
implementation may require that the address be aligned to page size (as
returned by sysconf). It does not say that the implementation may impose
further restrictions on the address.
> Thus that PA/Linux and Sparc/Linux are all non-conforming implementations
> because they require N > 1?
That's my reading, yes.
> I agree that POSIX might change their wording to say that SHMLBA
> is the right value to use, but I bet you'll never get the Austin Group
> to agree to this kind of change without a lot of work.
>
> Thus I'm happy to see some rationale text changes first :-)
Perhaps the place to start is an interpretation request to clarify whether
an implementation is allowed to impose a restriction on the bit-pattern of
the address other than it being aligned to page size.
Thanks,
Roland