Using hard links for debug builds

[Kim Barrett]

> On Jan 9, 2017, at 3:40 PM, Ioi Lam <ioi.lam at oracle.com> wrote:
> 
> Hi,
> 
> libjvm.so gets copied a few times during the build. I usually build slowdebug builds with --with-native-debug-symbols=internal (to make it easier with gdb). This gives me 8 libjvm.so files:
> 
> ./support/interim-image/lib/server/libjvm.so
> ./support/modules_libs/java.base/server/libjvm.so
> ./hotspot/variant-server/libjvm/gtest/libjvm.so
> ./images/test/hotspot/gtest/server/libjvm.so
> ./images/serverjre/lib/server/libjvm.so
> ./images/jdk/lib/server/libjvm.so
> ./images/jre/lib/server/libjvm.so
> ./jdk/lib/server/libjvm.so
> 
> Each of them is 320+MB. Even though I have a fast SSD, it's overwhelmed by the large churn and my machine becomes unresponsive for a long time.
> 
> The 8 libjvm.so files have 2 variants -- the gtest version (2 of them) vs the normal version (6 of them). Would it make sense to change the 'cp' to hard links instead?

Are reflinks available?  e.g. ‘cp —reflink …’  That might be a better solution than hard links.

> For now, I am doing a hack by patching this in the generated spec.gmk file:
> 
>    CP:=/bin/cp
> 
> to point to my script, which uses 'ln' instead of /bin/cp when dealing with libjvm.so ....