RFR(S): 8080684: PPC64: Fix little-endian build after "8077838: Recent developments for ppc"

[Vladimir Kozlov]

Looks good to me.

Thanks,
Vladimir

On 5/19/15 9:41 AM, Volker Simonis wrote:
> Hi,
>
> can I please get a review for the following fix of the ppc64le build.
>
> @Sasha, Tiago: I would be also especially interested if somebody with
> a little-endian ppc64 system can check if the fix really works there
> as I have currently no access to such a system.
>
> https://bugs.openjdk.java.net/browse/JDK-8080684
> http://cr.openjdk.java.net/~simonis/webrevs/2015/8080684/
>
> Following the details:
>
> On big-endian ppc64 we need so called 'function descriptors' instead
> of simple pointers in order to call functions. That's why the
> Assembler class on ppc64 offers an 'emit_fd()' method which can be
> used to create such a function descriptor.
>
> On little-endian ppc64 the ABI was changed (i.e. ABI_ELFv2) and
> function descriptors have been removed. That's why the before
> mentioned 'emit_fd()' is being excluded from the build with the help
> of preprocessor macros if the HotSpot is being build in a little
> endian environment:
>
> #if !defined(ABI_ELFv2)
> inline address emit_fd(...)
> #endif
>
> The drawback of this approach is that every call site which uses
> 'emit_fd()' has to conditionally handle the case where 'emit_fd()'
> isn't present as well. This was exactly the problem with change
> "8077838: Recent developments for ppc" which introduced an
> unconditional call to 'emit_fd()' in 'VM_Version::config_dscr() which
> lead to a build failure on little endian.
>
> A better approach would be to make 'emit_fd()' available on both,
> little- and big-endian platforms and handle the difference internally,
> within the function itself. On little-endian, the function will just
> return the current PC without emitting any code at all while the
> big-endian variant emits the required function descriptor.
>
> Thank you and best regards,
> Volker
>