I was surprised to read that Adobe discontinued the 64 bits version of Flash for Linux. While there is a new 32 bits version, and Adobe advises users to use the 32 bits version of Firefox instead.
Was wondering, as I didn't have to do that yet, is it that hard to port an application to 64 bits? Besides the libraries changes and the recompilation (settings in the Makefile), what makes the port difficult? (Flash is an example)
If you use a lot of ints and floats, it can be amazingly complex to get it to work suitably, esp. if it is a networked app.
It took over 2 years to port xMule to 64 bits and I don't believe its parent project, eMule, has 64 bit at all.
Ideally it should be a recompilation, in reality it takes a significant amount of effort. Even if it is simple there still has to be a full sweep by the QA team to prove it works and that always takes a while.
the coding part of porting to 64bits generally isn't that hard, but can require some time and a lot of hairpulling regarding builds/libs etc. however, the real problem, especially for a widely deployed project like flash is going through the proper testing coverage to cover the many code paths and platforms. 64bit is a horizontal feature, so it can possibly break everything, so everything needs to be tested.
for flash on linux in particular, its probably more of a cost-benefit issue. is catering to the percentage of users actually use linux and 64bit worth the development costs for adobe? probably not, at this point.
The obvious problems I guess would be variable sizes (e.g. longs are 64 bits on most 64 bit compilers), this messes up anything that uses size related operations such as bit shifting / some pointer arithmetic. I think adobe just can't be be bothered to scan through and ensure cross compatibility. Especially when 90%+ of browser use is on 32bit versions, I know flash hasn't ever worked on the 64bit IE but even 64bit Windows 7 defaults to the 32-bit version.
Lot of information on it here if your interested:
As noted in an Adobe blog post, Flash's ActionScript engine has a JIT compiler, that compiles the ActionScript code into native code.
x64 has a very different instruction set from x86. Therefore, making the JIT compiler generate x64 code is a non-trivial task, and is far more complicated than just making all the words 64 bits. :-)
The real kicker with porting apps to 64-bit is that every OS seems to treat the primitive types as they please. For example, under most linux environments a long is 4 bytes on a 32 bit system and 8 bytes on a 64 bit system (32bit=4bytes 64bit=8bytes.) Meanwhile, the int stays 4 bytes across 64bit and 32 bit systems. Under windows, the opposite seems to be true, the long stays consistently 4 bytes while the int switches between 32 and 64 bit.
That said, I have ported a medium sized project at work before from 32 bit to 64 bit linux (about 25,000 lines of code) only having to make changes in the the assembly code (GASM) which made several faulty assumptions about datatypes being 4 bytes long. Other than this, I had no problems, which suggests that provided you payed strict attention to your data types when you were first developing, porting should be seemless, perhaps only requiring certain compile switches be changed (like -fpic.) There were a few really bizzare corner cases that came up in my porting experience but I think they were mostly due to undefined behaviour of some GASM more than the porting itself.