On Thu, Mar 1, 2012 at 1:52 PM, Schwab,Wilhelm K <[email protected]>wrote:
> Eliot, > > That helps a bit; it's still unfamiliar territory. I am a little bothered > by #wordResult: and #floatResult. There are times when one is expected to > return 16 bit values (rare) and either a float or a double (common). Does > that flexibility exist? > Yes, the flexibility exists. But the mechanism needed to provide the flexibility is less than one might expect. For example, on x86 there are three fundamental return conventions, one for integral values, one for floating-point values, and one for structure values. See e.g. chapter 3 of the Sys V ABI for 386 (in my reply to Nicolas). Read it; it's good for the soul; makes one value Smalltalk's simplicity. Integral values are returned in %eax, %edx. edx is not used if the value fits in 32-bits. So the same sequence can be used to answer all integral values from 1 byte to 8 bytes, irrespective of sign. That said, I use two sequences, one for 32-bits or less and one for 33 to 64 bits. In your example of answering 16 bits one simply answers either the sign-extension of 16-bits (if signed) to 32-bits or the zero-extension of 16-bits to 32-bits (if unsigned). In any case, the result is answered in %eax, and it is up to the caller to access the result correctly. Float values are returned on the top of the floating point register stack (%st(0)). The same machine-code sequence can be used to answer single, double and extended precision floats, since on the fp stack, they are all represented in the same extended format. So on x86 the callback implementation supports 4 return mechanisms, retword, retword64, retdouble and retstruct. So far only two of these are fleshed out in Smalltalk code. But look at http://www.squeakvm.org/svn/squeak/branches/Cog/src/vm/vmCallback.h & http://squeakvm.org/svn/squeak/trunk/platforms/Cross/plugins/IA32ABI/ia32abicc.cand you'll see the other two. cheers, Eliot > > Bill > > > > > ------------------------------ > *From:* [email protected] [ > [email protected]] on behalf of Eliot Miranda [ > [email protected]] > *Sent:* Thursday, March 01, 2012 3:26 PM > *To:* [email protected] > *Subject:* Re: [Pharo-project] Alien signature: first attempt > > > > On Thu, Mar 1, 2012 at 10:57 AM, Schwab,Wilhelm K > <[email protected]>wrote: > >> Esteban, >> >> Will this work? Even if so, is there a better way to define it? >> > > No it won't work, because you don't understand what it does. > > >> >> longVoidStarLongRetInt: callbackContext sp: spAlien >> <signature: 'int (*) (long, void *, long)' abi: 'IA32'> >> ^callbackContext wordResult: >> (block >> value: (Alien newC:4) >> value: (Alien forPointer: (spAlien unsignedLongAt: >> 5)) >> value: (Alien newC:4) >> ) >> > > The above takes only one parameter's value from the spAlien (the void * > value) and passes garbage for the other parameters. The spAlien is a > pointer to the incoming C callback stack frame, i.e. a pointer to the > callback's parameters. So spAlien unsignedLongAt: 5 gets the four-byte > pointer for the void * parameter, wraps it up in a convenient pointer Alien > (so the callback block can e.g. indirect through it to get at the data the > pointer is pointing to), and passes it as the second argument of the > callback block. But the two Alien newC: 4's are entirely bogus, passing > effectively uninitialized data for the first and third parameters of the > callback block. They're just empty Aliens, when in fact you want to pass > two longs to the block for the first and third parameters. > > So to pass values in you need something like: > > longVoidStarLongRetInt: callbackContext sp: spAlien > <signature: 'int (*) (long, void *, long)' abi: 'IA32'> > ^callbackContext wordResult: > (block > value: (spAlien signedLongAt: 1) > value: (Alien forPointer: (spAlien unsignedLongAt: > 5)) > value: (spAlien signedLongAt: 9) > ) > > You might also need to consider passing the result of the block back > out. If you only want to use it to answer integers then the above is fine. > But take a look at the intcharstarRetint:sp: signature: > > intcharstarRetint: callbackContext sp: spAlien > <signature: 'int (*)(int, char *)' abi: 'IA32'> > ^callbackContext wordResult: > ((block > value: (spAlien signedLongAt: 1) ~= 0 > value: (Alien forPointer: (spAlien unsignedLongAt: 5)) strcpyUTF8) > ifNil: [0] > ifNotNil: > [:result| > result isInteger > ifTrue: [result] > ifFalse: [result == true ifTrue: [1] ifFalse: [0]]]) > > Analogously it passes a signed integer as the first argument and a UTF8 > string derived from the second char * parameter. (The method should > probably be called intcharstarasUTF8Retint:sp: or some such; forgive me, > we're getting there). > > But on return it takes the result of the callback block and passes it to > the ifNil:ifNotNil: which > - maps a nil result form the block to 0 (ifNil: [0]) > - maps integers to integers (which will only deal correctly with integers > in the 32-bit range), and > - maps true to 1, mapping all other results to 0. > > Does what's going on now make more sense? > > HTH, > Eliot > > >> Bill >> >> ________________________________________ >> From: [email protected] [ >> [email protected]] on behalf of Schwab,Wilhelm >> K [[email protected]] >> Sent: Thursday, March 01, 2012 12:15 AM >> To: [email protected] >> Subject: Re: [Pharo-project] FFI on 1.3: compile fields >> >> thanks!!!!! >> >> >> >> >> ________________________________________ >> From: [email protected] [ >> [email protected]] on behalf of Esteban >> Lorenzano [[email protected]] >> Sent: Wednesday, February 29, 2012 10:18 PM >> To: [email protected] >> Subject: Re: [Pharo-project] FFI on 1.3: compile fields >> >> you need to define a signature... not at home now, but wait 'til tomorrow >> and I'll send an example >> >> best, >> Esteban >> >> El 29/02/2012, a las 11:21p.m., Schwab,Wilhelm K escribió: >> >> > What does "cannot find callback signature" mean from #signature:block:? >> I'm stuck. >> > >> > >> > >> > >> > ________________________________________ >> > From: [email protected] [ >> [email protected]] on behalf of Esteban >> Lorenzano [[email protected]] >> > Sent: Wednesday, February 29, 2012 6:54 PM >> > To: [email protected] >> > Subject: Re: [Pharo-project] FFI on 1.3: compile fields >> > >> > yeah... sorry about that >> > is a bug on FFI... I managed to worked around it for HPDF, for a >> customer's project... but of course is not a good and definitive solution. >> > >> > best, >> > Esteban >> > >> > El 29/02/2012, a las 8:37p.m., Schwab,Wilhelm K escribió: >> > >> >> This is gonna take a while... I had structs flying around as void* >> and was moderately happy. Nonetheless, your suggestion worked, provided I >> add a lot getHandle asInteger and change the void* to long :( >> >> >> >> >> >> >> >> >> >> ________________________________________ >> >> From: [email protected] [ >> [email protected]] on behalf of Esteban >> Lorenzano [[email protected]] >> >> Sent: Wednesday, February 29, 2012 6:23 PM >> >> To: [email protected] >> >> Subject: Re: [Pharo-project] FFI on 1.3: compile fields >> >> >> >> I also found some problems using void* in linux... maybe you want to >> use long (which has same size)... I "fixed" my problems that way. >> >> >> >> yes... maybe we need to look at FFI to see why void* has problems some >> times, but well, that can help you atm (sorry for not having a better >> answer) >> >> >> >> Esteban >> >> >> >> El 29/02/2012, a las 8:11p.m., Igor Stasenko escribió: >> >> >> >>> On 1 March 2012 00:58, Schwab,Wilhelm K <[email protected]> >> wrote: >> >>>> Another glitch: is there any problem passing things as void*? I'm >> getting failure to coerce errors that did not arise before. >> >>>> >> >>> No idea. As you may suspect, i stopped using FFI/Alien once i got >> >>> NativeBoost toy to play with. >> >>> >> >>> Please file the issue, describing the problem. so we can look over it >> >>> and fix it. >> >>> >> >>>> >> >>>> >> >>>> ________________________________________ >> >>>> From: [email protected] [ >> [email protected]] on behalf of Igor Stasenko [ >> [email protected]] >> >>>> Sent: Wednesday, February 29, 2012 5:51 PM >> >>>> To: [email protected] >> >>>> Subject: Re: [Pharo-project] FFI on 1.3: compile fields >> >>>> >> >>>> On 1 March 2012 00:37, Schwab,Wilhelm K <[email protected]> >> wrote: >> >>>>> Does 1.3 by default not create field accessors? Why is that? I >> thought >> >>>>> nothing was happening. >> >>>>> >> >>>> >> >>>> Good question, i'd like to know the answer too. >> >>>> It is related to MC final 'installation' phase, >> >>>> where it initializing all classes. >> >>>> >> >>>> In NativeBoost i was also using >> >>>> >> >>>> noteCompilationOf: aSelector meta: isMeta >> >>>> "A hook allowing some classes to react to recompilation of >> certain selectors" >> >>>> >> >>>> but there was a big question, at which point this hook is triggered, >> >>>> and looks like some changes in MC stop triggering it/triggering at >> >>>> wrong time (not all methods get into a class/ class not initialized >> >>>> etc), >> >>>> which makes it not very useful. >> >>>> >> >>>> So i ended up creating a DNU handler on instance side, then on DNU i >> >>>> check if i have field accessors and if not, >> >>>> compile them on the fly. >> >>>> >> >>>> >> >>>>> Bill >> >>>>> >> >>>> >> >>>> >> >>>> -- >> >>>> Best regards, >> >>>> Igor Stasenko. >> >>>> >> >>>> >> >>> >> >>> >> >>> >> >>> -- >> >>> Best regards, >> >>> Igor Stasenko. >> >>> >> >> >> >> >> >> >> > >> > >> > >> >> >> >> >> > > > -- > best, > Eliot > > -- best, Eliot
