RFR: 8075533: Zero JVM segfaults for -version after JDK-8074552

[Volker Simonis]

Hi Severin,

I can't understand how SafeFetch32 and SafeFetchN are supposed to work
at all in Zero. The whole point of having the SafeFetch routines is to
have a possibility of peeking at potentially illegal memory addresses.
The current implementation of SafeFetch on Zero can not provide this
functionality so in my eyes it is useless.

I think we should do the following:
 - StubRoutines::SafeFetchN_stub() should just return 'null' on Zero
(this way the unmodified CanUseSafeFetchXX() routines would work for
Zero as well)
 - remove the implementations of  SafeFetchN and SafeFetch32 and set
StubRoutines::_safefetchN_entry and StubRoutines::_safefetch32_entry
to NULL in stubGenerator_zero.cpp (this will automatically make
StubRoutines::SafeFetchN_stub() return null on Zero)
 - the calls to test_safefetch32XX() should be guarded by
CanUseSafeFetchXX() (this woul avoid the Zero ifdefs in
stubRoutines.cpp)

The test changes are good.

Regards,
Volker


On Fri, Mar 20, 2015 at 12:57 PM, Severin Gehwolf <sgehwolf at redhat.com> wrote:
> Hi,
>
> Could somebody please review and sponsor this patch?
>
> The commit of JDK-8074552 broke the Zero port since it performs tests on
> JVM initialization if SafeFetch32 and SafeFetchN on invalid pointers
> (relying on a continuation scheme for safe fetch errors) work. Yet
> performing this test correctly requires support from the signal handler
> and access routines to ucontext_t which are missing for Zero.
>
> The intent of JDK-8074552 was to improve error reporting on SEGV's.
> Having this feature in Zero is less useful, since it's a C++ interpreter
> only environment.
>
> This patch disables the test and makes CanUseSafeFetch* functions return
> false unconditionally for Zero JVMs so as to not produce a recursive
> SEGV's during error reporting.
>
> I've also updated test SafeFetchInErrorHandlingTest.java so it's skipped
> for Zero.
>
> bug: https://bugs.openjdk.java.net/browse/JDK-8075533
> webrev:
> http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8075533/webrev.01/
>
> Testing done: make bootcycle-images fails before this patch and passes
> after for a Zero JVM on x86_64.
>
> Thanks,
> Severin
>