Re: __MIPSEL__ in sys32_rt_sigtimedwait

[Daniel Jacobowitz <dan@debian.org>]

On Tue, Jan 20, 2004 at 07:31:57PM +0100, Ralf Baechle wrote:
> On Tue, Jan 20, 2004 at 08:42:15PM +0300, Pavel Kiryukhin wrote:
> 
> > Hi all,
> > my question - does endiannes matters in sigset translation in 
> > sys32_rt_sigtimedwait (arch/mips/signal32.c)?
> 
> Think about where bit 33 ends for a big endian machine with an without
> the conversion.

No, I'm pretty sure Pavel's right.

-#ifdef __MIPSEB__
    case 1: these.sig[0] = these32.sig[0] | (((long)these32.sig[1]) << 32);
-#endif
-#ifdef __MIPSEL__
-    case 1: these.sig[0] = these32.sig[1] | (((long)these32.sig[0]) << 32);
-#endif

Consider a 64-bit sigset.  32-bit userland, 64-bit kernel.  Here's a
userland sigset with signal 33 set, only, on a little endian target.
Word 1, least significant bit, right?

byte address in memory
	1	2	3	4	5	6	7	8
val	0	0	0	0	0	0	0	1

Obviously, as a 64-bit integer the sigset looks different.  There it's
supposed to be 1 << (33 - 1).
val	0	0	0	1	0	0	0	0

So the correct algorithm to convert a userspace sigset to a kernel
sigset is to shift the second word left 32 bits, and leave the first
word right aligned, and or them together.  Which is what using the
__MIPSEB__ case does.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer