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    SubjectRe: [PATCH 2/5] powerpc: ftrace, convert to new dynamic ftrace arch API
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    On Mon, 2008-11-24 at 12:43 +1100, Paul Mackerras wrote:
    > Steven Rostedt writes:
    >
    > > Thanks to Paul Mackennas for pointing out the mistakes of my original
    >
    > Mackerras
    >
    > > +static int test_24bit_addr(unsigned long ip, unsigned long addr)
    > > +{
    > > + long diff;
    > > +
    > > + /*
    > > + * Can we get to addr from ip in 24 bits?
    > > + * (26 really, since we mulitply by 4 for 4 byte alignment)
    > > + */
    > > + diff = addr - ip;
    > > +
    > > + /*
    > > + * Return true if diff is less than 1 << 25
    > > + * and greater than -1 << 26.
    > > + */
    > > + return (diff < (1 << 25)) && (diff > (-1 << 26));
    >
    > I think this still isn't right, and the comment is one of those ones
    > that is only useful to people who can't read C, as it's just a
    > transliteration of the code.
    >
    > The comment should say something like "Return true if diff can be
    > represented as a 26-bit twos-complement binary number" and the second
    > part of the test should be (diff >= (-1 << 25)). However, since you
    > define a test_offset() function in patch 4/5 that does the same test
    > but using only one comparison instead of two, why don't you just say:
    >
    > return !test_offset(diff);
    >
    > (having first moved test_offset() before test_24bit_addr)?

    Or better still, split out and use the code from create_branch() in
    arch/powerpc/lib/code-patching.c .. which is hopefully correct :)

    cheers

    --
    Michael Ellerman
    OzLabs, IBM Australia Development Lab

    wwweb: http://michael.ellerman.id.au
    phone: +61 2 6212 1183 (tie line 70 21183)

    We do not inherit the earth from our ancestors,
    we borrow it from our children. - S.M.A.R.T Person
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