Re: [PATCH 17/21] powerpc: Add missing prototype for sys_debug_setcontext

[Mathieu Malaterre]

Michael,

On Thu, Mar 8, 2018 at 11:36 AM, Michael Ellerman <mpe@xxxxxxxxxxxxxx> wrote:
> Mathieu Malaterre <malat@xxxxxxxxxx> writes:
>
>> On Sun, Mar 4, 2018 at 11:54 AM, Michael Ellerman <mpe@xxxxxxxxxxxxxx> wrote:
>>> Mathieu Malaterre <malat@xxxxxxxxxx> writes:
>>>
>>>> In commit 81e7009ea46c ("powerpc: merge ppc signal.c and ppc64 signal32.c")
>>>> the function sys_debug_setcontext was added without a prototype.
>>>>
>>>> Fix compilation warning (treated as error in W=1):
>>>>
>>>>   CC      arch/powerpc/kernel/signal_32.o
>>>> arch/powerpc/kernel/signal_32.c:1227:5: error: no previous prototype for âsys_debug_setcontextâ [-Werror=missing-prototypes]
>>>>  int sys_debug_setcontext(struct ucontext __user *ctx,
>>>>      ^~~~~~~~~~~~~~~~~~~~
>>>> cc1: all warnings being treated as errors
>>>
>>> This one should actually be using the SYSCALL_DEFINE syntax, so that it
>>> can be used with CONFIG_FTRACE_SYSCALLS.
>>>
>>> See eg. our mmap:
>>>
>>>   SYSCALL_DEFINE6(mmap, unsigned long, addr, size_t, len,
>>>                 unsigned long, prot, unsigned long, flags,
>>>                 unsigned long, fd, off_t, offset)
>>>   {
>>>         return do_mmap2(addr, len, prot, flags, fd, offset, PAGE_SHIFT);
>>>   }
>>>
>>>
>>> We probably still need this patch, but I'm not entirely sure because the
>>> SYSCALL_DEFINE macro does all sorts of shenanigans.
>>
>> I see. Could you please drop this patch then. The patch does not look
>> that trivial anymore. I'll need to dig a bit more on how to do the
>> syscall stuff with a 7 params function.
>
> Ergh, yuck, seems we're the first suckers to need do that.
>
> I think I'll take this patch for now, it's still good for now at least,
> and then the SYSCALL_DEFINE stuff can be an addition.

Just to close the loop (for later reference). Here is what Al Viro
told me about this function

[begin quote]
int sys_debug_setcontext(struct ucontext __user *ctx,
                         int ndbg, struct sig_dbg_op __user *dbg,
                         int r6, int r7, int r8,
                         struct pt_regs *regs)

can't be converted to SYSCALL_DEFINE... not because it's a 7-argument
syscall (it isn't); the problem is that the last argument here does
*not* come from userland.  What it really is trying to be is
3-argument syscall:
SYSCALL_DEFINE3(debug_setcontext, struct ucontext __user *, ctx,
                                  int, ndbg,
                                  struct sig_dbg_op __user *, dbg)
with no dummy r6/r7/r8.  The thing is, ppc dispatcher combines the
"pass 6 arguments" and "pass pt_regs *" by passing both.

debug_setcontext(), swapcontext(), sigreturn() and rt_sigreturn() are,
AFAICS, the only ppc syscalls that make use of that argument.  All of
those are relying upon regs == current_pt_regs() == current->thread.regs,
[...]
But in any case, these are not 7-argument syscalls - debug_setcontext(2)
and swapcontext(2) are 3-argument and sigreturn()/rt_sigreturn() have
no arguments at all.
[end quote]

Sorry about the wrong analysis in the number of arguments count. I
believe commit 0d60619e1c0ca (powerpc/next) should be just fine for
now.

2cts