RFC: 8136978 Much nearly duplicated code for vmError support

[Sebastian Sickelmann]

Hi,

i have looked at the enhancement JDK-8136978 and have 2 solutions how
this could be handled and want to ask which seems to be more
"hotspot-code-style" like.

The common idea behind the change is to move os/linux/vmError_linux.cpp
to os/posix/vmError_posix.cpp and change the methods appropriate. Remove
of os_[*]/vmError_[*].cpp (for [*] = aix,bsd,solaris and linux)

I want to concentrate on the "signals stuff" in this mail.

Calls to os::Linux::ucontext_set_pc  and os::Linux::ucontext_get_pc will
be changed to os::Posix::.......
Calls to pthread_sigmask will be replaced with
os::Posix::unblock_signals(const sigset_t *set).

These methods are defined in os/posix/os_posix.hpp.
I think unblock_signals should be implemented in os/[*]/vm/os_[*].cpp
like this:

    int os::Posix::unblock_signals(const sigset_t *set) {
      return pthread_sigmask(SIG_UNBLOCK, set, NULL);
    }

But for ucontext_set_pc and ucontext_get_pc i see two variants:

Implement in in os/[*]/vm/os_[*].cpp like this:
   
    address os::Posix::ucontext_get_pc(ucontext_t* ctx) {
      return os::Linux::ucontext_get_pc(ctx);
    }

and call the existing methods from the os_cpu directory.

Or remove the ucontext_get_pc and ucontext_set_pc from the
os/[*]/vm/os_[*].hpp and change the implementations in
os_cpu/*/vm/os_[*]_[**].cpp from os::[*]::ucontext.......   to
os::Posix::ucontext.........

I think the solutions are identically from the view of the compile
result at least when inlining is used.

I think the first solutions would creates a smaller changeset.
I think the second solution would lead to a slightly smaller codebase.

What do you think? I personally prefer the second.

-- Sebastian