On Wed, 2008-09-24 at 08:45 +0200, Arnd Bergmann wrote: > On Wednesday 24 September 2008, Benjamin Herrenschmidt wrote: > > Why do we want it ? > > > > It's an int, it's zero extended, but that should still be a valid signed > > 32 bits int in compat_sys_select() or do I miss something ? > > IIRC, the calling conventions on 64 bit ppc assume that a signed int > argument is sign-extended into a 64 bit register. The compat syscall > entry point does not know which registers are signed or unsigned, so > it will always to zero-extend, making the register contain an undefined > bit pattern (e.g. 0x00000000fffffffe), which may be interpreted as being > a positive number. An explicit cast as it is done in ppc32_select turns > this into a well-defined 32-bit number stored in a 64-bit register (e.g. > 0xfffffffffffffffe).
If that is true, then _any_ syscall that takes an int value must have a ppc specific sign-extending compat wrapper, are you sure that is the case ? Ben. _______________________________________________ Linuxppc-embedded mailing list Linuxppc-embedded@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-embedded