[Vm-dev] bug on windows ioShowDisplay for bitdepth 16/8/4 (big endian)

Sat May 10 14:11:21 UTC 2014

2014-05-07 1:32 GMT+02:00 Eliot Miranda <eliot.miranda at gmail.com>:

>
> Hi Nicolai,
>
>
> On Tue, May 6, 2014 at 4:14 AM, Nicolai Hess <nicolaihess at web.de> wrote:
>
>>
>> 2014-05-05 20:37 GMT+02:00 Eliot Miranda <eliot.miranda at gmail.com>:
>>
>>>
>>> Hi Nicolai,
>>>
>>>
>>> On Mon, May 5, 2014 at 12:06 AM, Nicolai Hess <nicolaihess at web.de>wrote:
>>>
>>>>
>>>> 2014-04-03 17:51 GMT+02:00 karl ramberg <karlramberg at gmail.com>:
>>>>
>>>>>
>>>>> I can confirm this bug on windows Cog.
>>>>>
>>>>> Cheers,
>>>>> Karl
>>>>>
>>>>>
>>>>> On Thu, Apr 3, 2014 at 10:11 AM, Nicolai Hess <nicolaihess at 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)
>>
>
> Yes, I think you're exactly right (IIRC).
>
> 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.
>>
>
> Ah, so the hope is that the older syntax will work on all versions?  That
> would be sweet.
>

No, actually I hope, that the recommended syntax works with all versions.
It is difficult to setup a complete build environment with the older
gcc-versions.
(Do we really need compatiblity with gcc 2.95?)

Anyway, I installed the core gcc-binaries for
2.95
3.3.1
4.7.2
and just took the assembler output.
They don't generate the "same" code, but all generating working code.
-> move argument from stack to X
-> do operation on X
-> move argument back

So,
#   define BYTE_SWAP(w) __asm__("bswap %0" : "+r" (w))
#   define WORD_SWAP(w) __asm__("roll $16, %0" : "+r" (w))
works.

>
>
>>
>> I'll test this with different gcc versions and compare the compiler output
>>  (after I found out how to install multiple mingw versions :) )
>>
>>
>> nicolai
>>
>>
>>
>>
>
>
> --
> best,
> Eliot
>
>
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