[RFA] Fix float argument passing in inferior function calls for ppc64

[Thiago Jung Bauermann]

Hi,

The 64-bit PowerPC ELF ABI version 1.9 says that "single precision
floating point values are mapped to the second word in a single
doubleword". The ppc64_sysv_abi_push_dummy_call function in
ppc-sysv-tdep.c, however, implements version 1.7 of the ABI which says
that they should go in the first doubleword.

Because of this, if you are calling a function with many arguments and
some need to be passed on the stack, GDB will get it wrong for 32-bit
floats. This is why in Linux/ppc64 GDB fails the "Call function with
many float arguments" test posted here:

http://sourceware.org/ml/gdb-patches/2008-01/msg00291.html

This patch fixes the test. It makes GDB pass 32-bit floats in the second
word when passing them in the stack as stated in the current ABI.

I didn't touch the code which writes the float to a general register in
the first word because I'm not sure how to test it. It is probably
related to soft-float, I guess.

Tested on Linux/ppc64 with no regressions. I believe this will also fix
other operating systems supported by GDB on ppc64 since they use the
same push_dummy_call implementation (assuming they also follow the
current SysV ABI), but I don't have the means to test them either.

Maybe someone could test the patch and the testcase in *BSD? Luis' patch
which has the testcases would also need this testing.
-- 
[]'s
Thiago Jung Bauermann
Software Engineer
IBM Linux Technology Center
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