RFR(M): 8016697: PPC64 (part 5): Use stubs to implement safefetch

[Volker Simonis]

Hi Goetz,

I think the change is good and if the other reviewers don't decide to
implement it for the current platforms we can push it.

By the way, the makefile changes in ppc64.make will follow in patch 8 for
linux [1] and patch 14 for aix [2].
The implementation of the stubs will be in patch 9 for linux [3] and patch
15 for aix [4] (only the signal handling part).

Regards,
Volker

[1]
http://hg.openjdk.java.net/ppc-aix-port/jdk8/hotspot/file/tip/ppc_patches/0008_linux_ppc_make_changes.patch
[2]
http://hg.openjdk.java.net/ppc-aix-port/jdk8/hotspot/file/tip/ppc_patches/0014_aix_make_changes.patch
[3]
http://hg.openjdk.java.net/ppc-aix-port/jdk8/hotspot/file/tip/ppc_patches/0009_linux_ppc_files.patch
[4]
http://hg.openjdk.java.net/ppc-aix-port/jdk8/hotspot/file/tip/ppc_patches/0015_aix_ppc_files.patch



On Mon, Jun 17, 2013 at 3:55 PM, Lindenmaier, Goetz <
goetz.lindenmaier at sap.com> wrote:

>  Hi,****
>
> ** **
>
> the PPC64 port uses stub routines to implement safefetch. We had and****
>
> have problems with inline assembly, especially with non-gcc****
>
> compilers. Stub routines allow to implement safefetch without****
>
> depending on OS or compiler, as it's the case with the current****
>
> implementation. This also allows to use a single implementation if an****
>
> architecture is supported on several os platforms.****
>
> ** **
>
> http://cr.openjdk.java.net/~goetz/webrevs/8016697-safefetch/****
>
> ** **
>
> Currently, we guard the code with ****
>
>   #ifdef SAFEFETCH_STUBS****
>
> which is set in ppc64.make.****
>
> ** **
>
> I could also imagine an implementation that uses a pd_debug flag****
>
> or a const flag set in os_<os_cpu>.hpp that allows the C-compiler to ****
>
> optimize, and writing the code like this:****
>
> ** **
>
> extern "C" int pd_SafeFetch32 (int * adr, int errValue) ;****
>
> extern "C" intptr_t pd_SafeFetchN (intptr_t * adr, intptr_t errValue) ;***
> *
>
> inline int SafeFetch32(int* adr, int errValue) {****
>
>   if (UseSafefetchStub) {****
>
>     assert(StubRoutines::SafeFetch32_stub(), "stub not yet generated");***
> *
>
>     return StubRoutines::SafeFetch32_stub()(adr, errValue);****
>
>   } else {****
>
>     pd_SafeFetch32(adr, errValue);****
>
>   }****
>
> }****
>
> ** **
>
> Unfortunately this requires ****
>
>   1) setting the flag on all platforms****
>
>   2) renaming the safefetch function on all platfoms.****
>
> ** **
>
> Actually I would prefer this second solution as it avoids the
> preprocessor, ****
>
> and am happy to edit the sources accordingly if this finds acceptance.****
>
> ** **
>
> For the implementation of a safefetch_stub see****
>
>
> http://hg.openjdk.java.net/ppc-aix-port/jdk8/hotspot/file/fce884e5ba0b/src/cpu/ppc/vm/stubGenerator_ppc.cpp
> ****
>
> ** **
>
> Could I get a review on this change, please?****
>
> ** **
>
> Thanks,****
>
>   Goetz.****
>
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