RFR: JDK-8202384: Introduce altserver jvm variant with

[Baesken, Matthias]

Hi Erik , is there  some info available about  the performance impact when  disabling  disabling speculative execution  ?



And which compiler versions are needed for this ?



Best regards, Matthias





>We need to add compilation flags for disabling speculative execution to

>our native libraries and executables. In order to allow for users not

>affected by problems with speculative execution to run a JVM at full

>speed, we need to be able to ship two JVM libraries - one that is

>compiled with speculative execution enabled, and one that is compiled

>without. Note that this applies to the build time C++ flags, not the

>compiler in the JVM itself. Luckily adding these flags to the rest of

>the native libraries did not have a significant performance impact so

>there is no need for making it optional there.

>

>This patch defines flags for disabling speculative execution for GCC and

>Visual Studio and applies them to all binaries except libjvm when

>available in the compiler. It defines a new jvm feature

>no-speculative-cti, which is used to control whether to use the flags

>for libjvm. It also defines a new jvm variant "altserver" which is the

>same as server, but with this new feature added.

>

>For Oracle builds, we are changing the default for linux-x64 and

>windows-x64 to build both server and altserver, giving the choice to the

>user which JVM they want to use. If others would prefer this default, we

>could make it default in configure as well.

>

>The change in GensrcJFR.gmk fixes a newly introduced race that appears

>when building multiple jvm variants.

>

>Bug: https://bugs.openjdk.java.net/browse/JDK-8202384

>

>Webrev: http://cr.openjdk.java.net/~erikj/8202384/webrev.01