2014-05-05 20:37 GMT+02:00 Eliot Miranda <eliot.miranda@gmail.com>:

 

Hi Nicolai,

On Mon, May 5, 2014 at 12:06 AM, Nicolai Hess <nicolaihess@web.de> wrote:

 

2014-04-03 17:51 GMT+02:00 karl ramberg <karlramberg@gmail.com>:

 

I can confirm this bug on windows Cog.

Cheers,

Karl

On Thu, Apr 3, 2014 at 10:11 AM, Nicolai Hess <nicolaihess@web.de> wrote:

 

There is still something wrong with byte/word swap in windows ioShowDisplay code
attached are two screenshots

squeak 4.5 image with cogvm from http://files.pharo.org/vm/cogmt/win/

pharo 30793 image with latest vm from http://files.pharo.org/vm/pharo/win/

showing this bug after setting the Display depth to 16
(Display newDepth:16)

sqwin32window.c has three variants for doing the byte_swap/word_swap on

bitdepths with big endian to convert to lsb

This one is active and causes this error.

#  if __GNUC__ >= 3
#   define BYTE_SWAP(w) __asm__("bswap %0" : "=r" (w) : "r" (w))
#   define WORD_SWAP(w) __asm__("roll $16, %0" : "=r" (w) : "r" (w))

This one would work
#  else
#   define BYTE_SWAP(w) __asm__("bswap %%eax" : "=eax" (w) : "eax" (w))
#   define WORD_SWAP(w) __asm__("roll $16, %%eax" : "=eax" (w) : "eax" (w))

This one, of course, works too
# else
#  define BYTE_SWAP(w) w = (w << 24) | ((w & 0xFF00) << 8) | ((w >> 8) & 0xFF00) | (w >> 24)
#  define WORD_SWAP(w) w = (( (unsigned)(w) << 16) | ((unsigned) (w) >> 16))

This one is not there but would work (at least with gcc > 4.5
#   define BYTE_SWAP_MY(w) __asm__("bswap %0" : "+r" (w))
#   define WORD_SWAP_MY(w) __asm__("roll $16, %0" : "+r" (w))

But actually I don't know assembler and/or the gcc inline code syntax, so
I don't know what is wrong with the first version :)

Nicolai

btw, you can not test this bug with the current squeak 4.5 all in on image,
as it uses a rather old vm.

Third screenshot:
using the latest stable pharo-vm, it looks much more wrong, as there
was another(?) bug that is fixed already(?) - i don't know :)

Someone else can reproduce this?

(eliot?, nicolas? )

It is easily fixable, I think. But I am not good at inline assembler.

I'll open a mantis and fogbugz report.

Yes, I can reproduce it.  But I've not had time to check with a pre 3.x and a post 3.x compiler to check what the right syntax is.  I'm busy with other stuff right now.  Hopefully I'll get to this in a coupel of weeks. Anyone else out there who can provide the right syntax for

2.95

3.4.x

4.x

I'd be very grateful and simply integrate the fix. 

-- 

best,

Eliot

Ok, thank you eliot.

I think I know now way the first version does not work:
__asm__("bswap %0" : "=r" (w) : "r" (w))

The compiler might generate code like this, just:

bswap %ebx

without initialisation of that register (although we declare "r"(w) as input).
It behaves like that, because an output register is supposed to be overwritten :)

and the bswap command only uses the %0 (the first register in the output : input register list).

The proper way for defining an register as output-input (or read-write register) would be

__asm__("bswap %0" : "+r" (w) )

Some asm-inline tutorials mention, this(the "+" constraint modifier) would not work on all compilers and
prefer another older syntax:
 __asm__("bswap %0" : "=r" (w)  : "0" (w))

(use the 0th output register for input too)

But even the gcc2.95 doc (http://gcc.gnu.org/onlinedocs/gcc-2.95.3/gcc_16.html#IDX955)

lists "+" as allowed constraint modifier, so, I think it should work.

I'll test this with different gcc versions and compare the compiler output

(after I found out how to install multiple mingw versions :) )

nicolai