Re: [patch 1/1] dm: fix printk warnings about whether %lu/%Lu is right for sector_t

From: Anton Altaparmakov (aia21_at_cam.ac.uk)
Date: 10/08/04

  • Next message: Lee Revell: "Re: [PATCH] Realtime LSM" 
    Date:	Fri, 8 Oct 2004 22:57:25 +0100 (BST)
To: Paolo Giarrusso <blaisorblade_personal@yahoo.it>

    On Fri, 8 Oct 2004, Paolo Giarrusso wrote:
    > On Friday 08 October 2004 22:11, Anton Altaparmakov wrote:
    > > On Fri, 8 Oct 2004, Andrew Morton wrote:
    > > > blaisorblade_spam@yahoo.it wrote:
    > > Actually %Ld is completely wrong. I know in the kernel it makes no
    > > difference but people see it in the kernel and then go off an use it in
    > > userspace and it generates junk output on at least some architectures.
    > Well, gcc does not complain, and the problem is not "kernel is special" or "on
    > some arch it's different". It's an alias for "ll" for both gcc and glibc; I
    > checked, in fact, the version below of info pages for glibc:

    gcc is not the only compiler and glibc is not the only C library.

    > This is Edition 0.10, last updated 2001-07-06, of `The GNU C Library
    > Reference Manual', for Version 2.3.x of the GNU C Library.
    > (I guess the "last update" is botched).
    >
    > > This is because %L means "long double (floating point)" not "long long
    > > integer" and when you stuff an integer into it it goes wrong (on some
    > > architectures)...
    > I think an all ones, or at least on i386.

    Yes I know in the kernel and on i386 it makes no difference, I said that
    already. But on some systems it does make a difference. I have seen it
    myself and I have had it reported. Thinking about it when I said
    architectures I possibly meant to say "other Unix flavours", I think one
    of the *BSDs was the one where I saw the difference between %L and %ll
    manifest itself.

    > > From the printf(3) man page:
    > Outdated.

    Sorry, it is not. I find it somewhat strange that you choose gcc and
    glibc to say what is correct... Ever heard of standards?!?

    Quoting from C99 standard (ISO/IEC 9899:1999(E)):

    [cut here]
    ll (ell-ell) Specifies that a following d, i, o, u, x, or X conversion
                 specifier applies to a long long int or unsigned long long
                 int argument; or that a following n conversion specifier
                 applies to a pointer to a long long int argument.
    [snip]
    L Specifies that a following a, A, e, E, f, F, g, or G
                 conversion specifier applies to a long double argument.

    If a length modifier appears with any conversion specifier other than as
    specified above, the behavior is undefined.
    [cut here]

    So the C99 standard specifies the use of %L with an integer type
    conversion specified is undefined. So relying on %L being an alias for
    %ll considering there are systems where this is not the case seems stupid
    to me but hey I don't really care. I just thought I would let people who
    don't know it know. If you want to carry on using %L because it works in
    the kernel be my guest.

    Best regards,

            Anton

    PS. Just don't submit patches containing %L for fs/ntfs/* or I will flame
    you to crisp as we share code with userspace libntfs and ntfsprogs and I
    and other NTFS developers care about our code being portable and working
    on as many architectures and OS as possible. (-; 

    -- 
Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @)
Unix Support, Computing Service, University of Cambridge, CB2 3QH, UK
Linux NTFS maintainer / IRC: #ntfs on irc.freenode.net
WWW: http://linux-ntfs.sf.net/ & http://www-stu.christs.cam.ac.uk/~aia21/
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  • Next message: Lee Revell: "Re: [PATCH] Realtime LSM"

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