Re: [9fans] gcc on plan9

[Roman Shaposhnik <rvs@sun.com>]

Ronald G Minnich wrote:
> IMHO, you know more than I do at this point!
Relatively speaking ;-) I once tried to do the same thing I do with 
these 500+ apps with everything that's
available through the Gentoo portage system. To say that I was surprised 
would be a gross
understatement. :-(

> So, what's our problem :-) Is all hope lost?
> Is this mess fixable? If so, how?
Now that I understand your goal (which is to provide a way for running a 
preselected
set of  HPC apps on a Plan9 system) and I can stop confusing it with 
inventing a magic
G-wand  I'd say that your biggest challenge will be to carefully 
retarget the apps in
question from (L)POSIX/C++ environment. I don't believe its a lost 
cause, but it all
depends on how messy the apss will turn out to be.

I don't know much about the apps, but here's a list of issues I 
personally confronted
while porting Sun Studio C/C++ compiler from Solaris to Linux:

It doesn't matter whether its C, C++ or Fortran --  nowadays its all 
about autotools/libtool
recognizing your system, and let me tell you these guys are *wild*. Case 
in point: when we
first ported our seed C compiler autoconf was convinced that it was a 
PGI compiler running
on an Open?BSD system  -- go figure. Once you get past configuring the 
apps,  every C/C++
compiler gets confronted with two essential interfaces: glibc and 
linker/ELF. For a C compiler
dependency  on ELF is less  of an issues, but for a C++ one its a pretty 
big deal. In fact
we had seriously considered porting Solaris ld to Linux just so that we 
don't have to depend
on GNU ld messing up object files (we ended up fixing GNU ld, but its a 
different story).
Next comes the glibc, which in turn, depends on Linux kernel headers and 
wants to get into
compiler business all the time by providing "kosher"  crt*.o and 
demanding a certain way
of tickling its internals for things like IEEE floating point support to 
work properly.

The biggest problem with all of this is that the way C99 (and portions 
of the C++) standard
are structured makes it impossible to have a properly functioning 
application unless
you have glibc support in certain areas. One of the  reasons GCC can't 
claim
C99 compliance is because glibc sucks (you can find more on that right here:
http://gcc.gnu.org/gcc-4.1/c99status.html).

Now, you say that you're going to use APE and there I have serious 
doubts that things
like FP exception handling and C99 complex will work for you. These two 
proved
to be quite essential for the set of HPC apps I have internally from 
*our* customers.

Now, suppose that you've overcome all of that. What's next ? C++ of course!

C++ with things like templates instantiations in ELF COMDAT sections and 
exception
handling support places lots of additional requirements on how flexible 
linker should
be in handling ELF files. Speaking of which -- do you intend to port ELF 
to Plan9 as well ?

Once you get past codegeneration the glibc will rear its ugly head once 
again. This time
around it'll be about supporting C++ header files which are just there 
to wrap around
standard C headers in the latest and greatest std:: namespace. Of 
course, I'm talking
about things like <cstring> and <cstdlib>. There again you will start 
battling how
gcc configures itself on different systems and how it all can be hooked 
up to APE.
       
Oh, and there's also a question of what to do about MT apps. I'd be very 
curious to
know how would you go about solving it on Plan9 as far as PTHREADS are 
concerned.
Or may be your apps don't use any (which I find hard to believe for an 
HPC market).

That's about it when it comes to the biggies. The sort of things I 
distinctly remember
suffering through on a personal level.

On the application level you still have to tame dependencies on things 
which go beyond
the scope of C99 or ISO C++ standards, but that's a story for another day.
>>   Well, all I can say is -- its a pity that even more resources will
>>   be spent on proliferating gcc's bad influence on application 
>> developers.
>
> The world  sucks. I could not agree more. Propagating all this gnu 
> stuff is depressing, makes me wish I did something else for a living 
> sometimes. I sort of watch with amazement as people work on the 
> segment layout of their ELF files, and discuss what to inline. arg!
>
> thanks, I think you've educated me (I'm dead serious).
    Well, I'm glad my emails weren't in vain. I'm very curious to see 
how far you can go with the approach
you've chosen, and I'd be glad to share more of the porting experience. 
Feel free to drop me emails
on this subject. I've been there and there's a chance I might be able to 
help you guys.

Thanks,
Roman.