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

Hi Mathieu,

Mathieu Malaterre [off-list ref] writes:

On Thu, Mar 8, 2018 at 11:36 AM, Michael Ellerman [off-list ref] wr=

ote:

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Mathieu Malaterre [off-list ref] writes:

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On Sun, Mar 4, 2018 at 11:54 AM, Michael Ellerman [off-list ref] =

wrote:

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Mathieu Malaterre [off-list ref] writes:

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In commit 81e7009ea46c ("powerpc: merge ppc signal.c and ppc64 signal=

32.c")

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the function sys_debug_setcontext was added without a prototype.

Fix compilation warning (treated as error in W=3D1):

  CC      arch/powerpc/kernel/signal_32.o
arch/powerpc/kernel/signal_32.c:1227:5: error: no previous prototype =

for =E2=80=98sys_debug_setcontext=E2=80=99 [-Werror=3Dmissing-prototypes]

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 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=

);

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  }


We probably still need this patch, but I'm not entirely sure because t=

he

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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 =3D=3D current_pt_regs() =3D=3D current->thre=

ad.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]

Awesome follow-up thanks.

I should have realised that's what the code was doing, but I didn't look
closely enough. Apologies to Al for having to stare at our horrible
signal code again :)

We should really clean all that up, I can't see any reason those
syscalls aren't using current_pt_regs().

That would then mean we could use SYSCALL_DEFINE.

I wrote that down so we don't (might not) forget:

  https://github.com/linuxppc/linux/issues/131

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

No worries.

cheers