[PATCH] PowerPC: Extend fpu fenv operations to operate on 64-bit FPSCR

[Ryan S. Arnold]

Greetings,

For some reason when I posted this to libc-alpha@sourceware.org it
didn't make it out to the email inboxes so I'm resending.

The included patch provides the following changes to extend the FPSCR
(floating point status and control register) to 64-bits for PowerPC
POWER6 and POWER6x:

o For PowerPC in general it redefines fpu_control_t from an unsigned
long int to an unsigned long long int so that the entire 64-bit FPSCR on
POWER6 can be saved/restored.  On non-POWER6 hardware the high-order
32-bits are simply discarded/ignored for all operations.

  It is necessary to change it for all PowerPC because the loader is
built as the default PowerPC arch (i.e. non-POWER6) and uses the
rtld_global_ro struct which contains an fpu_control_t and therefore must
be able to load a libc built for POWER6 or non-POWER6 (which also uses
the rtld_global_ro struct).

  Any difference in size of fpu_control_t between the loader and libc
will cause libc to access rtld_global_ro struct members at the wrong
offsets from where the structure was populated by the loader.

  The impact is minimal since currently the fpu_control_t is initially
populated from a double anyway and the fpu_control_t type is not used
dynamically in any external function and thus, no symbol versioning is
required.

o Provides a conditional implementation of _FPU_GETCW and _FPU_SETCW
which operate on either the entire 64-bit FPSCR on POWER6[x] or simply
the low-order 32-bits of the fpu_control_t on non-POWER6[x].

o Provides granular control over the high order 32 bits of the FPSCR
that aren't reserved.

o Provides an overridden sysdeps/powerpc/math/test-fpucw that verifies
that the high-order word is saved to the FPSCR and restored using the
_FPU_[GET|SET]CW macros.  It also verifies that there are no deleterious
effects on non-POWER6 systems.

o Provides conditional definitions of the PowerPC fenv helper macros
(fesetenv_register & fegetenv_register) which are used by the fenv
functions to set/get the contents of the FPSCR.

o Provides sysdeps/powerpc/math/test-powerpc-fenv which tests the
high-order word save/restore using the fe[set|get]env_register
functions.

o Replaces the FPSCR restore with a macro which will provide a 64-bit
restore on POWER6 for swapcontext and setcontext.

o Replaces some of the magic number fenv masks in the fenv functions
with a define that better describes what the magic number means.

I successfully executed build and runtime tests (make check) on POWER5
(32-bit FPSCR) as well as POWER6 (64-bit FPSCR).

Ryan S. Arnold
IBM Linux Technology Center
Linux Toolchain Development
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