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

[Mikael Vidstedt]

Dean,

Can I suggest that you turn the logic around to instead list/test for 
the platforms where we know we can use the nonpic optimization? That way 
we'll avoid running into this type of problem again.

Cheers,
Mikael

On 2012-06-18 00:07, Dean Long wrote:
> 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