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    SubjectRe: [PATCH 00/23] tracehook
    From: Roland McGrath <>
    Date: Thu, 17 Jul 2008 00:25:41 -0700 (PDT)

    > I have done some arch work and will submit this to the arch maintainers
    > after the generic tracehook series settles in. For now, that work is
    > available in my GIT repositories, and in patch and mbox-of-patches form
    > at

    Thanks for doing this work.

    I took a quick look at the sparc64 tracehook support and only spotted
    one issue.

    You'll need special handling for 32-bit compat tasks when copying the
    arguments in. You can't just use the full 64-bit values because they
    get 32-bit zero extended by the 32-bit syscall entry code, and this
    doesn't propagate into the pt_regs copies.

    See arch/sparc64/kernel/syscalls.S:linux_sparc_syscall32

    So at a minimum, when _TIF_32BIT is set, you'll need to "u32" cast
    the regs->u_regs[] values before assigning them into the unsigned long
    array slots.

    Actually, it's more complicated than that. We have to sign extend
    arguments in some cases, and this is performed by a class of stubs
    in arch/sparc64/kernel/sys32.S which then revector to the real
    system call handler.

    I don't know how you want to handle those cases. Should the tracehook
    user know that it's a 32-bit task, what system call it is, and therefore
    do the appropriate sign extensions? That doesn't sound right.

    So likely we have to properly sign extend those things here in the
    asm/syscall.h handlers.

    If you look at arch/sparc64/kernel/sys32.S it uses macros and then a
    list of cases that could be slightly modified such that they could be
    used to build argument sign extension tables. Simply change the
    explicit register name arguments to pure numbers (ie. %o0 becomes
    plain 0) and adjust the assembler macros accordingly.

    Then, in a C file somewhere, you set these macro defines differently
    then feed the list of instantiations through them and build the table.

    The other arch's with compat support will have this same exact issue.

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