review request for 7156729: PPC: R_PPC_REL24 relocation error related to some libraries built without -fPIC

[Dean Long]

http://cr.openjdk.java.net/~dlong/7156729/
Summary of changes:    8 lines changed: 7 ins; 0 del; 1 mod; 40 unchg

Non-PIC objects have a limited range when calling external functions, so 
dynamic linking can fail if for example libc is too far away.  The 
solution is to build all powerpc objects with -fPIC, including the oops 
and gc directories that were previously excluded.  This causes calls to 
go through the PLT.  PIC_ARCH is a list that can be expanded later (ARM 
could be next).  I also tried using -mlongcall instead of -fPIC, but it 
doesn't have any performance advantage over -fPIC and it causes a 17% 
increase in static footprint vs. a 5% decrease for -fPIC.

To measure the performance regression, I ran some refworkload benchmarks 
with different heap sizes.  As expected, the smaller the heap, the 
bigger the slowdown.  With a 32m heap, specjvm98 "javac" slows down by 
2.5%.  The GC logs show about a 6% slowdown in pause times.

There are some known issues with -fPIC overhead in the current 
toolchain, so we expect to gain much of the performance back in the 
future when we can move to a newer toolchain.  But since this is 
targeted for 7u6/hs23.2, there isn't much choice for now.

dl