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Re: 64-bit gotcha

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On 12/3/11 12:20 PM, Arne Vajhøj wrote:
> On 12/3/2011 5:47 AM, Roedy Green wrote:
>> A Java Web Start program I wrote a long time ago suddenly stopped
>> working. It sets the System clock to an atomic time server.
>>
>> I discovered the problem was it uses a 32--bit DLL via JNI and my
>> default Java is 64 bit. It cannot use 32-bit DLLs.
>>
>> That surprises me. I would have thought MS would have had to come up
>> with a way of doing that since so many DLLs would not yet be available
>> in 32-bit. Maybe it can in general, but just not in Java.
>
> 32 bit or 64 bit is a per process thing.
>
> You can't have part of a process using 32 bit addresses and
> another part using 64 bit addresses.

True, Windows does not support that.  But it's technically feasible, and 
in fact 32-bit Windows supported 32-bit processes calling 16-bit DLLs 
(e.g. http://support.microsoft.com/kb/155763).

It's a fair question to ask why Microsoft didn't do the same for 32-bit 
DLLs executing in 64-bit processes.

I don't personally have the answer.  Could be a simple matter of 
practicality (e.g. thunking was not beneficial enough for Win32 to 
justify its cost and so was not done for x64 Windows), or it might be 
that thunking relied on some CPU feature that supported 16-bit 
addressing in a 32-bit process that doesn't exist for 
32-bit-addressing-in-64-bit-processes.

I don't know.

But saying "you can't do it" doesn't really seem to answer the question. 
  Roedy already knows he can't do it, at least in Java, and implicit in 
his post is the question as to why Windows does not support calling 
32-bit DLLs in 64-bit processes.

> The JVM and native DLL's must have same bitness.
>
> It is not Java specific.
>
> If you are using C# then you can specify AnyCPU (32 bit or 64 bit),
> x86 (32 bit only) and x64 (64 bit only) to stamp programs with
> requirements.

But as with Java, you cannot call native DLLs using the wrong bitness of 
a .NET program.  A .NET program running as a 32-bit process can call 
only 32-bit DLLs, and a .NET program running as a 64-bit process can 
call only 64-bit DLLs.  Other than the way that the choice is made for 
what kind of bitness the program is running in, it's pretty much the 
same situation.

Pete

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Thread

64-bit gotcha Roedy Green <see_website@mindprod.com.invalid> - 2011-12-03 02:47 -0800
  Re: 64-bit gotcha Arne Vajhøj <arne@vajhoej.dk> - 2011-12-03 15:20 -0500
    Re: 64-bit gotcha Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-12-03 14:01 -0800
      Re: 64-bit gotcha Roedy Green <see_website@mindprod.com.invalid> - 2011-12-03 18:17 -0800
        Re: 64-bit gotcha Martin Gregorie <martin@address-in-sig.invalid> - 2011-12-04 12:06 +0000
          Re: 64-bit gotcha Jeff Higgins <jeff@invalid.invalid> - 2011-12-04 08:57 -0500
            Re: 64-bit gotcha Jeff Higgins <jeff@invalid.invalid> - 2012-02-25 19:15 -0500
              Re: 64-bit gotcha Martin Gregorie <martin@address-in-sig.invalid> - 2012-02-26 00:53 +0000
                Re: 64-bit gotcha Jeff Higgins <jeff@invalid.invalid> - 2012-02-25 20:26 -0500
          Re: 64-bit gotcha Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-12-04 10:04 -0400
        Re: 64-bit gotcha Arne Vajhøj <arne@vajhoej.dk> - 2012-03-12 19:50 -0400
      Re: 64-bit gotcha Travers Naran <tnaran@gmail.com> - 2011-12-04 09:17 -0800
      Re: 64-bit gotcha Joshua Cranmer <Pidgeot18@verizon.invalid> - 2011-12-04 18:33 -0600
        Re: 64-bit gotcha Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-12-04 16:56 -0800
        Re: 64-bit gotcha Arne Vajhøj <arne@vajhoej.dk> - 2012-03-12 19:53 -0400
      Re: 64-bit gotcha Arne Vajhøj <arne@vajhoej.dk> - 2012-03-12 19:49 -0400

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