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    SubjectRe: Understanding Linux addr space, malloc, and heap
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    On Fri, 2005-10-21 at 16:37 +0100, Alex Bligh - linux-kernel wrote:
    >
    > --On 21 October 2005 17:22 +0200 Arjan van de Ven <arjan@infradead.org>
    > wrote:
    >
    > > Ok I meant in the "while adhering to the standard" :)
    >
    > More precisely, as per the man page:
    > > POSIX.1b says that mprotect can be used only on regions of memory
    > > obtained from mmap(2).
    >
    > But what is interesting (if anything) is this:
    > > ERRORS
    > > EINVAL addr is not a valid pointer, or not a multiple of
    > > PAGESIZE.
    >
    > So if he calls mprotect with memory allocated by malloc (which should
    > fail), why doesn't he get EINVAL? He says it returns 0 (meaning it
    > succeeded). Which it shouldn't (unless he is stupendously lucky in
    > malloc's allocation, in which case it should work).

    it succeeds all right; it just does other things than you expect
    perhaps ;)

    your alignment code had a bug, so it would align potentially to the
    wrong piece of memory


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