Remove glibc from alpine_jdk11

[basil]

JDK-8247589 was backported to OpenJDK 11.0.16 upstream (slated for a July 19, 2022 GA) in openjdk/jdk11u-dev#910, but it appears to have been backported to Adoptium/Temurin sooner than that in adoptium/jdk11u#7 and is already shipping in Temurin 11.0.15. As a result it is no longer necessary to include glibc.

Testing done

Built this Docker image. Verified that java is not linking against glibc:

$ ldd /opt/java/openjdk/bin/java
        /lib/ld-musl-x86_64.so.1 (0x7f1ec5295000)
        libjli.so => /opt/java/openjdk/bin/../lib/jli/libjli.so (0x7f1ec527e000)
        libc.musl-x86_64.so.1 => /lib/ld-musl-x86_64.so.1 (0x7f1ec5295000)
        libz.so.1 => /lib/libz.so.1 (0x7f1ec5264000)

Installed Jenkins and verified there were no errors or stack traces printed in the console log. Then went to the script console and induced a crash:

import java.lang.reflect.Field
import sun.misc.Unsafe

Field f = Unsafe.class.getDeclaredField("theUnsafe")
f.setAccessible(true)
Unsafe unsafe = (Unsafe) f.get(null)
unsafe.putAddress(0, 0)

Examining the resulting HotSpot error file, I see that musl is loaded in the process address space:

$ grep -i musl /tmp/hs_err_pid6.log
7fe98557e000-7fe985593000 r--p 00000000 00:52 50                         /lib/ld-musl-x86_64.so.1
7fe985593000-7fe9855db000 r-xp 00015000 00:52 50                         /lib/ld-musl-x86_64.so.1
7fe9855db000-7fe985611000 r--p 0005d000 00:52 50                         /lib/ld-musl-x86_64.so.1
7fe985611000-7fe985612000 r--p 00092000 00:52 50                         /lib/ld-musl-x86_64.so.1
7fe985612000-7fe985613000 rw-p 00093000 00:52 50                         /lib/ld-musl-x86_64.so.1

Additionally I see the following strings:

libc:musl - unknown musl - unknown
vm_info: OpenJDK 64-Bit Server VM (11.0.15+10) for linux-amd64-musl JRE (11.0.15+10), built on Apr 19 2022 22:14:51 by "" with gcc 10.3.1 20211027

The former indicates that https://github.com/adoptium/jdk11u/blob/982989d67b04ab2c4047c31acbf02e82b55c3072/src/hotspot/os/linux/os_linux.cpp#L626= must have been executed, which implies MUSL_LIBC must have been defined when compiling the software.

[basil]

Consistent with https://github.com/adoptium/containers/blob/df60032f19531a9c7effc22c3c994f9428277700/11/jdk/alpine/Dockerfile.releases.full#L24=.

[timja]

Nice!