lkml.org 
[lkml]   [2003]   [Feb]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: Is -fno-strict-aliasing still needed?
    Horst von Brand wrote:
    >
    > Art Haas <ahaas@airmail.net> said:
    > > I ask because I've just built a kernel without using that flag -
    > > linus-2.5 BK from this morning, probably missing the 2.5.60 release by
    > > a few hours.
    >
    > The problem with strict aliasing is that it allows the compiler to assume
    > that in:
    >
    > void somefunc(int *foo, int *bar)
    >
    > foo and bar will _*never*_ point to the same memory area (at the same
    > struct, or into the same array, etc). There is no way to check for this in
    > the compiler in general (the function and the call might be in different
    > files, many functions are being called via pointers, ...).

    I though pointers to the same type, such as int *, could alias still.

    But pointers to different types, such as int* and short* is assumed
    to never clash with strict aliasing. And this bites linux
    because it sometimes choose to see "two adjacent shorts as one int" for
    performance reasons.

    I remember the flag was introduced because some IP or TCP
    code do exactly this, and converting it all to unions would
    render that code unreadable.

    Helge Hafting
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2005-03-22 13:33    [W:0.038 / U:61.816 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site