RFR(m): 8074552: SafeFetch32 and SafeFetchN do not work in error handling

[Thomas Stüfe]

Hi David,

Ouch. The only thing I can think about are the added initialization tests
in stubRoutines.cpp. I will check this.

Kind Regards, Thomas



On Mon, Mar 9, 2015 at 6:56 AM, David Holmes <david.holmes at oracle.com>
wrote:

> Hi Thomas,
>
> FYI When I applied this to latest hs-rt forest and ran through JPRT the
> Windows fastdebug builds were DOA (instant segfault just running "java
> -version"). Can't see how your changes could do this so running a test on
> unmodified forest.
>
> David
>
>
> On 9/03/2015 9:40 AM, David Holmes wrote:
>
>> Hi Thomas,
>>
>> Minor nit: in src/share/vm/runtime/stubRoutines.cpp::test_safefetchN can
>> you use UCONST64 macro instead of explicit ULL - thanks.
>>
>> Otherwise this seems okay, but we will also need the aarch64 component
>> (and I'll look into our internal needs).
>>
>> Thanks,
>> David
>>
>> On 7/03/2015 2:10 AM, Thomas Stüfe wrote:
>>
>>> Hi all,
>>>
>>> could someone please review the following fix (I also will need a
>>> sponsor):
>>>
>>> http://cr.openjdk.java.net/~stuefe/webrevs/8074552/webrev.01/
>>>
>>> https://bugs.openjdk.java.net/browse/JDK-8074552
>>>
>>> The fix will make SafeFetch[32,N] work in error reporting.
>>>
>>> At SAP, we use SafeFetch a lot in error reporting to poke around in
>>> potentially invalid memory (e.g. writing hex dumps over areas which
>>> may be
>>> partly unmapped), and we feel that this could be useful for the
>>> OpenJDK too.
>>>
>>> Without this fix, SafeFetch will cause a crash, the current error
>>> reporting
>>> step will be interrupted and error reporting will continue with the next
>>> step; that is not optimal because the interrupted step may have shown
>>> valuable information.
>>>
>>> This fix handles SafeFetch faults during error reporting the same way as
>>> they are handled normally. The changes are:
>>>
>>> - handle safe fetch fault in the various (os_cpu dependend) secondary
>>> signal handlers
>>>
>>> - provide a function to check if it is safe to use SafeFetch:
>>> CanUseSafeFetch32(). SafeFetch needs stub routines and will crash when
>>> used
>>> before stub generation.
>>>
>>> - set_context_pc() is added which complements the existing
>>> get_context_pc()
>>> and all instances where the pc in ucontext_t was modified directly are
>>> changed to use set_context_pc()
>>>
>>> - in stubRoutines.cpp, a small test was added to the already existing
>>> stub
>>> routines tests which run at VM init
>>>
>>> - in vmError.cpp, a test was added to test SafeFetch during error
>>> reporting, similar to the tests introduced for 8065895
>>>
>>> - A JTreg test was added
>>>
>>> Thanks and Kind Regards,
>>>
>>> Thomas Stuefe
>>>
>>>