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    SubjectRe: want to clarify powerpc assembly conventions in head.S and entry.S
    On Tue, 2004-04-13 at 00:31, Chris Friesen wrote:
    > Benjamin Herrenschmidt wrote:
    > >>You knew this was coming... What's special about syscalls? There's the
    > >>r3 thing, but other than that...
    > >
    > > The whole codepath is a bit different, there's the syscall trace,
    > > we can avoid saving much more registers are syscalls are function
    > > calls and so can clobber the non volatiles, etc...
    > It appears that we always enter the kernel via "transfer_to_handler",
    > and return via "ret_from_except". Is this true? (I'm running on at
    > least a 74xx chip.)

    ret_from_syscall for syscalls, hash_page also has a different
    return to userland path, and load_up_{fpu,altivec} have their own
    retturn path.
    On ppc32 currently, the entry is almost always the same except for
    hash_page and load_up_{fpu,altivec}

    > I want to insert two new bits of code, one that gets called before the
    > exception handler when we drop from userspace to kernelspace, and one as
    > late as possible before going back to userspace. I need to catch
    > syscalls, interrupts, exceptions, everything.
    > The entry one I planned on putting in "transfer_to_handler", just before
    > "addi r11,r1,STACK_FRAME_OVERHEAD".
    > I was planning on putting the exit one just after the "restore_user"
    > label. Will this catch all possible returns to userspace?



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