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    SubjectRe: [PATCH] perf: Incorrect use of snprintf results in SEGV

    * Peter Zijlstra <peterz@infradead.org> wrote:

    > On Wed, 2012-03-07 at 21:37 +0100, Ingo Molnar wrote:
    > > size_needed = snprintf_size(...);
    >
    > This would require 3 passes over the fmt+args, first to find
    > the allocated size is insufficient, 2nd to compute the size,
    > 3rd to fill buffer.

    No. The 1% case would use this separate API with its quirky
    return value. snprintf_size() works like today's snprintf, it's
    just *named* clearly to signal that it returns something not
    quite intuitive and results in bugs even in code that *tries* to
    be aware of the corner cases.

    > Whereas with the current "creative" API only 2 passes are
    > needed.
    >
    > I can imagine that back in the day of small memory and small
    > CPU this was deemed important enough.
    >
    > Anyway, its all moot, this API exists and has been out in the
    > wild for several decades now, its not like we can actually
    > change it :-)

    Of course it is moot - I am not arguing for a change in the API.

    But the self-justification, as outlined in the mail I replied
    to, is brutally wrong, and nowhere in this discussion did I see
    the important notion mentioned that the *common case matters* -
    so maybe reading this will keep others from committing the same
    mistake, with newly introduced APIs.

    Thanks,

    Ingo


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