RFR(xxs): 8172579: 8168503 broke AIX build

[Thomas Stüfe]

Dear all,

please take a look at this tiny fix:

Bug: https://bugs.openjdk.java.net/browse/JDK-8172579
Webrev:
http://cr.openjdk.java.net/~stuefe/webrevs/8172579-colon-8168503-broke-AIX-build/webrev/common/autoconf/hotspot.m4.udiff.html

JDK-8168503 exposed a bug in AIX grep. AIX grep, when called like this:
"grep -Fx <patternlist>" is unable to handle empty patterns correctly.
8168503 added a line break in the definition of a variable:

 VALID_JVM_FEATURES="compiler1 compiler2 zero shark minimal dtrace jvmti
jvmci \
-    graal fprof vm-structs jni-check services management all-gcs nmt cds
static-build aot"
+    graal fprof vm-structs jni-check services management all-gcs nmt cds \

+    static-build link-time-opt aot"


So now, "cds" is followed by multiple spaces, which are later expanded to
multiple newlines, and grep is unable to match the pattern immediately
preceding these newlines (in this case, "cds"). This causes the
HOTSPOT_VALIDATE_JVM_FEATURES
function to fail with "Invalid JVM feature: cds".

The error would also happened before when trying to match "jvmci", but so
far we do not build jvmci on powerpc.

The workaround for now is just to remove the superfluous spaces.

I tried for some hours to find a better solution but could not find one
which was small enough and worked on all platforms.

I tried using sed to change multiple spaces to a single space, but did not
get it to work correctly on AIX either.

I thought about passing the pattern list as file to grep - which opposed to
passing the pattern in the command line works as expected - but refrained
from this because creating temporary files is error prone.

I attempted to change the whole NEEDLE/STACK expression to a loop checking
each single feature with '=~' against the list of valid features, but this
felt too intrusive.

The proposed fix is not the most elegant one but the risk for other
platforms is minimal and it works.

Kind Regards, Thomas