Re: Help on memchr() EGLIBC assembly code

[Richard Henderson <rth7680@gmail.com>]

On 07/13/2009 03:16 PM, Matt Turner forwarded:
>>>> The problem is that the memchr() function on alpha uses prefetch, which
>>>> can cause a page boundary to be crossed, while the standards (POSIX and
>>>> C99) says it should stop when a match is found.

That's not supposed to matter -- faults from prefetch are supposed to be 
ignored; see do_page_fault:

         /* As of EV6, a load into $31/$f31 is a prefetch, and never faults
            (or is suppressed by the PALcode).  Support that for older CPUs
            by ignoring such an instruction.  */
         if (cause == 0) {
                 unsigned int insn;
                 __get_user(insn, (unsigned int __user *)regs->pc);
                 if ((insn >> 21 & 0x1f) == 0x1f &&
                     /* ldq ldl ldt lds ldg ldf ldwu ldbu */
                     (1ul << (insn >> 26) & 0x30f00001400ul)) {
                         regs->pc += 4;
                         return;
                 }
         }

Can you figure out why that kernel code isn't working?  I no longer have 
working alpha hw...


r~