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    SubjectRe: 64-syscall args on 32-bit vs syscall()
    Benjamin Herrenschmidt wrote:
    > err = syscall(SYS_fallocate, fd, mode, offset, len);
    >
    > With "offset" being a 64-bit argument.
    >
    > This will break because the first argument to syscall now shifts
    > everything by one register, which breaks the register pair alignment
    > (and I suppose archs with stack based calling convention can have
    > similar alignment issues even if x86 doesn't).
    >
    > Ulrich, Steven, shouldn't we have glibc's syscall() take a long long as
    > it's first argument to correct that ? Either that or making it some kind
    > of macro wrapper around a __syscall(int dummy, int sysno, ...) ?
    >
    > As it is, any 32-bit app using syscall() on any of the syscalls that
    > takes 64-bit arguments will be broken, unless the app itself breaks up
    > the argument, but the the order of the hi and lo part is different
    > between BE and LE architectures ;-)
    >
    > So is there a more "correct" solution than another here ? Should powerpc
    > glibc be fixed at least so that syscall() keeps the alignment ?

    There are several problems with syscall(), not just this - because a
    number of system calls in section 2 of the manual don't map directly
    to kernel syscalls with the same function prototype.

    Even fork() has become something complicated in Glibc that doesn't use
    the fork syscall :-(

    So anything using syscall() has to be careful on Linux already.
    Changing the 64-bit alignment won't fix the other differences.

    -- Jamie


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