RS: [Beowulf] Sempron compile optimization

[Martin Siegert]

On Thu, Nov 24, 2005 at 10:17:41AM +1100, Chris Samuel wrote:
> On Thursday 24 November 2005 10:13, Steffen Persvold wrote:
> 
> > However, I do think it is rather annoying that gcc on ppc64 produces 32bit
> > binaries by default.
> 
> Indeed.

Actually, people may think differently about that: 32bit code may
run slightly faster. Thus, if you do not need the address space you
just as well can compile in 32 bit mode.

> > I  believe the IBM compiler produce 64bit.
> 
> Unfortunately not.
> 
> $ xlc hello.c -o t2
> 1506-503 (W) Option "-qlongdouble / -qldbl128" is not supported for LINUX for Power.

This looks like a misconfiguration to me - you should not get that error
message:

$ xlc -o t2 hello.c
$ file t2
t2: ELF 32-bit MSB executable, PowerPC or cisco 4500, version 1 (SYSV), for GNU/Linux 2.2.5, dynamically linked (uses shared libs), not stripped
$ xlc -q64 -o t2 hello.c
$ file t2
t2: ELF 64-bit MSB executable, cisco 7500, version 1 (SYSV), for GNU/Linux 2.4.21, dynamically linked (uses shared libs), not stripped

> $ file t2
> t2: ELF 32-bit MSB executable, PowerPC or cisco 4500, version 1 (SYSV), for GNU/Linux 2.2.5, dynamically linked (uses shared libs), not stripped
> 
> Hey ho, at least it's consistently disappointing.. :-)

Defaults are more or less a matter of taste ...
What is really disappointing is that most (?) configure scripts (and
libtool, etc.) break when you compile in 64bit mode (xlc -q64 ...
or gcc -m64 ...): Even though x86_64 is around for a while now I still
run into numerous configure scripts that blindly search /usr/X11R6/lib
for libX11.so and after finding it there try to compile with
-L/usr/X11R6/lib -lX11 without checking that that library is actually
useless when -m64 is specified and that they should have looked in
/usr/X11R6/lib64 instead (or better not specify -L... at all and
let the compiler find the library itself).

- Martin

-- 
Martin Siegert
Head, HPC at SFU
WestGrid Site Manager
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