RFR(S): 8221175: Fix bad function case for controlled JVM crash on PPC64 big-endian

[Lindenmaier, Goetz]

> Should I run it against submit tests before pushing? It's a change in shared
> code, but it can't affect other architectures.
I think it's safe to be pushed.

Best regards,
  Goetz.


> 
> Best regards,
> Gustavo
> 
> > Best, Goetz
> >
> >> -----Original Message-----
> >> From: ppc-aix-port-dev <ppc-aix-port-dev-bounces at openjdk.java.net> On
> >> Behalf Of Gustavo Romero
> >> Sent: Sonntag, 24. März 2019 20:21
> >> To: Thomas Stüfe <thomas.stuefe at gmail.com>
> >> Cc: ppc-aix-port-dev at openjdk.java.net; Daniel D. Daugherty
> >> <daniel.daugherty at oracle.com>; hotspot-runtime-dev at openjdk.java.net
> >> Subject: Re: RFR(S): 8221175: Fix bad function case for controlled JVM crash
> on
> >> PPC64 big-endian
> >>
> >> Hi Thomas!
> >>
> >> On 03/23/2019 05:43 PM, Thomas Stüfe wrote:
> >>> Hi Gustavo,
> >>>
> >>> looks good.
> >>
> >> Thanks a lot for reviewing it and for your comments!
> >>
> >>
> >>> Would be nice to cleanly factor function descriptor handling out at some
> >> point: we have various pieces, e.g. a struct FunctionDescriptor in
> >> assembler_ppc.hpp, a resolve function in os_aix.cpp, now this... also, I
> believe,
> >> on AIX there is a struct FunctionDescriptor in os headers, but I may
> remember
> >> this wrong.
> >>>
> >>> But cleanup can be done in a different change.
> >>
> >> Unfortunately I don't have access to AIX systems, so I can't test/work on AIX
> >> (that's one of the reasons I decided to CC ppc-aix-port-dev).
> >>
> >> I overlooked 'struct FunctionDescriptor' presence. All headers look in place,
> so
> >> how about using FunctionDescritor instead of an array?
> >>
> >> webrev v2:
> >>
> >> http://cr.openjdk.java.net/~gromero/8221175/v2/
> >>
> >> Cheers,
> >> Gustavo
> >>
> >>> Thanks for fixing!
> >>>
> >>> Cheers, Thomas
> >>>
> >>>
> >>> On Fri, Mar 22, 2019 at 5:15 PM Gustavo Romero
> >> <gromero at linux.vnet.ibm.com <mailto:gromero at linux.vnet.ibm.com>>
> >> wrote:
> >>>
> >>>      Hi,
> >>>
> >>>      Please, could I get reviews for the following change?
> >>>
> >>>      bug   : https://bugs.openjdk.java.net/browse/JDK-8221175
> >>>      webrev: http://cr.openjdk.java.net/~gromero/8221175/v1/
> >> <http://cr.openjdk.java.net/%7Egromero/8221175/v1/>
> >>>
> >>>      It fixes the way a function pointer is defined in order to call a bad
> function
> >>>      at address 0xF (controlled crash case 13) on PPC64 big-endian
> machines.
> >>>
> >>>      On PPC64 big-endian compiler defaults to ABI ELFv1 which mandates
> >> function
> >>>      pointers to part of a function descriptor, at offset 0 [1].
> >>>
> >>>      Currently the SIGISEGV being generated by case 13 is incorrect because
> if a
> >>>      function descriptor is not use to call the bad function address the
> program
> >>>      segfaults before effectively calling the function, when trying to load
> >>>      the (bad) function pointer from offset 0 of base address 0xF, so before
> >>>      branching to the function.
> >>>
> >>>      It does not affect PPC64 little-endian machines because by default ABI
> >> ELFv2
> >>>      is used (instead of ABI ELFv1) and for that ABI no function descriptor is
> >>>      defined / employed.
> >>>
> >>>      The fix consists in defining properly a function descriptor with a bad
> >> function
> >>>      at offset 0 (the following offset are no important in that case) and using
> >> that
> >>>      function descriptor to call the bad function, only on PPC64 big-endian
> >> machines.
> >>>
> >>>      That issue was found when investigating the JDK-8220794 issue [2].
> >>>
> >>>      Thank you.
> >>>
> >>>      Best regards,
> >>>      Gustavo
> >>>
> >>>      [1] http://refspecs.linuxfoundation.org/ELF/ppc64/PPC-
> >> elf64abi.html#FUNC-DES
> >>>      [2] https://bugs.openjdk.java.net/browse/JDK-8220794
> >>>
> >