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

[Lindenmaier, Goetz]

Looks good, too.

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
> >