A special jtreg version for jcov was released at
/java/jct-tools/pkgs/jct-tools-214-jtreg.jcov/promoted.19Sep
prior to merlin.

The following jtreg option is no longer working in Mustang.
"-Xrunjcov:file=/net/sqe/global/nfs/some-where/jtreg.jcov"

Mustang disabled JVMPI by default. JVMPI is enabled only by passing another flag introduced in Mustang, "-XX:+UseUnsupportedDeprecatedJVMPI". There are other optional flags to get coverage data effectively.

The jtreg special version seemed not designed to take additional required JCOV runtime flags. Here is an example of jcov runtime flags used in functional tests;
-Xrunjcov:file=/net/sqe/global/nfs/some-where/jtreg.jcov -XX:+UseUnsupportedDeprecatedJVMPI -Xms256m -Xmx256m -XX:+EnableJVMPIInstructionStartEvent -XX:-UseFastEmptyMethods -XX:-UseFastAccessorMethods

The first 2 runtime flags are required and others are optional. Please allow jtreg be passed any number of jcov flags.