Arch Linux

lapack is compiled on x86_64 with -fPIC because it can't be compiled without.

As for -fPIC in general and in particular on x86, quite often it slows things down instead of speeding things up (I have not looked into this particular package yet). Do you have any benchmarks and statements to backup your claim for this package?

Hi Ronald,

Thank you very much for your response and I am by no means an expert in this.
To get really good performance for, e.g., scientific libraries one should probably
link against static libraries anyways.

For shared objects, it is not know at compile time at what particular virtual address
the *.so will be loaded at run/load-time. A PIC compiled shared object is set up to deal
with this and can be accessed by all applications requiring the library independently
of where the *.so was loaded in virtual memory via the global offset table (GOT).
This incurs some cost during compilation (the -fPIC part) and results in a slightly larger
library size.
If a shared object is compiled with non-PIC code the dynamic linker at run-time has to
replace all direct memory references in the *.so and relocate these addresses.
For large libraries with lots of relocations this can lead to
a significant performance degradation. There's more info regarding this issue
at [1], [2], and [3]. That said, I have no hard numbers how much this cost turns out to
be for blas/lapack and these numbers might be fairly hard to come by. However,
I think the general consensus as far as I understand it is that shared objects should be
PIC. Last but not least (at least for me as a PAX user), these non-PIC shared objects
don't run on systems with a kernel that prevents run-time text relocations for security
reasons (PAX, SELinux) just like x86_64's NX bit, since this is a possible attack vector

Best,
Markus

[1] http://sources.redhat.com/autobook/autobook/autobook_71.html#SEC71
[2] http://www.gentoo.org/proj/en/hardened/pic-guide.xml
[3] http://people.redhat.com/drepper/dsohowto.pdf

thanks for your efforts on this Markus. I just want you to know that I will only have time after christmas to look into this. Please poke me if I have not done anything before the start of next year ;)

Hi Ronald,

That sounds great and I wish you relaxing holidays.

cheers,
Markus