Hotspot symbol visibility - surprising news!

[Daniel Jeliński]

Hi Magnus,

The "massive generated mapfile" is used on Windows. As you noticed, on
Linux symbols are exported if they are both JNIEXPORT and listed in
the mapfile. On Windows, the symbols are exported if they are either
JNIEXPORT or listed in the mapfile. The Windows symbolicator needs to
see the vftables to tell apart different object types, and these
tables are only made available in the produced binaries through the
mapfile. The Windows mapfile exports the vftables of every virtual
class in libjvm, which is much more than the symbolicator actually
needs, but that's probably a separate topic.

The symbolicator on Linux does not need the mapfile.

The assembly functions are correctly labelled with .globl; if we
remove these declarations or change them to local, the code won't
link. The right solution here is to also label them as .hidden, for
example using this script:

     sed -i -n 'p;s/\.globa\?l/.hidden/p' src/hotspot/os_cpu/*/*.S

The symbols from the standard libraries are not exported by any of our
binaries. Libjvm removes them via the use of mapfile, and all other
libraries are linked with  -Wl,--exclude-libs,ALL; if you choose to
remove the mapfile from libjvm, you'll need to add that parameter.

Regards,
Daniel