Re: [jakub@redhat.com: Re: [brian.j.vandecoevering@intel.com: RE: [Linux-ia64] problems with ppp/ppp

[Bjorn Helgaas <bjorn.helgaas@hp.com>]

__put_user_check in both the 2.4 and 2.5 BK trees looks like the
one quoted below, so evidently the problem has not been fixed.
If you have a proposed fix, a patch and a test case would be
useful.

On Friday 12 December 2003 8:37 am, Bill Nottingham wrote:
> Back long ago, I reported a problem with PPP on ia64:
> 
>  http://www.gelato.unsw.edu.au/linux-ia64/0105/1641.html
> 
> We added the workaround in our tree for earlier releases,
> and promptly forgot about it; however, someone reported that
> RHEL 3 has the same issue (as we took the workaround out.)
> 
> Jakub noticed the following - does this explain the problem?
> 
> Bill
> 
> ----- Forwarded message from Jakub Jelinek <jakub@redhat.com> -----
> 
> From: Jakub Jelinek <jakub@redhat.com>
> To: notting@redhat.com
> Subject: Re: [brian.j.vandecoevering@intel.com: RE: [Linux-ia64] problems with ppp/pppd: put_user/copy_to_user]
> Reply-To: Jakub Jelinek <jakub@redhat.com>
> User-Agent: Mutt/1.4.1i
> X-Reply-To: Jakub Jelinek <jakub@redhat.com>
> Date: Fri, 12 Dec 2003 07:32:59 -0500
> 
> On Thu, Dec 11, 2003 at 09:16:50PM -0800, David S. Miller wrote:
> > On Thu, 11 Dec 2003 22:58:48 -0500
> > Bill Nottingham <notting@redhat.com> wrote:
> > 
> > > According to Intel, this patch is *still* needed to fix ppp on
> > > ia64 in RHEL3. We should probably verify this, although I'm
> > > still at a loss as to why it works.
> > 
> > Either a compiler problem or their put_user() implementation
> > is busted.
> 
> The latter I guess.
> At least linux-2.4.22-1.2108.nptl I have unpacked on my box
> has in asm-ia64/uaccess.h:
> 
> #define put_user(x,ptr) __put_user_check((__typeof__(*(ptr)))(x),(ptr),sizeof(*(ptr)),get_fs())
> 
> #define __put_user_check(x,ptr,size,segment)                    \
> ({                                                              \
>         register long __pu_err asm ("r8") = -EFAULT;            \
>         __typeof__(*(ptr)) *__pu_addr = (ptr);                  \
>         if (__access_ok((long)__pu_addr,size,segment)) {        \
>                 __pu_err = 0;                                   \
>                 switch (size) {                                 \
>                   case 1: __put_user_8(x,__pu_addr); break;     \
>                   case 2: __put_user_16(x,__pu_addr); break;    \
>                   case 4: __put_user_32(x,__pu_addr); break;    \
>                   case 8: __put_user_64(x,__pu_addr); break;    \
>                   default: __put_user_unknown(); break;         \
>                 }                                               \
>         }                                                       \
>         __pu_err;                                               \
> })
> 
> #define __put_user_32(x,addr)                                                           \
>         asm volatile (                                                                  \
>                 "\n"_LL"\tst4 %1=%r2%P1\t// %0 gets overwritten by exception handler\n" \
>                 "\t.xdata4 \"__ex_table\", @gprel(1b), @gprel(1f)\n"                    \
>                 _LL                                                                     \
>                 : "=r"(__pu_err) : "m"(__m(addr)), "rO"(x), "0"(__pu_err))
> 
> But, a function call clobbers r8.
> Guess a
> __typeof(x) __x = (x);
> before __pu_err and
> s/x/__x/ is needed.
> Probably __pu_addr decl should be moved before __pu_err is initialized too,
> otherwise
> extern int *foo ();
> put_user (0, foo ());
> might not work properly.
> 
> 	Jakub
> 
> 
> 
> ----- End forwarded message -----