In fill_thread_core_info() the ptrace accessible registers are collected
for a core file to be written out as notes. The note array is allocated
from a size calculated by iterating the user regset view, and counting the
regsets that have a non-zero core_note_type. However, this only allows for
there to be non-zero core_note_type at the end of the regset view. If
there are any in the middle, fill_thread_core_info() will overflow the
note allocation, as it iterates over the size of the view and the
allocation would be smaller than that.

To apparently avoid this problem, x86_32_regsets and x86_64_regsets need
to be constructed in a special way. They both draw their indices from a
shared enum x86_regset, but 32 bit and 64 bit don't all support the same
regsets and can be compiled in at the same time in the case of
IA32_EMULATION. So this enum has to be laid out in a special way such that
there are no gaps for both x86_32_regsets and x86_64_regsets. This
involves ordering them just right by creating aliases for enum’s that
are only in one view or the other, or creating multiple versions like
REGSET32_IOPERM/REGSET64_IOPERM.

So the collection of the registers tries to minimize the size of the
allocation, but it doesn’t quite work. Then the x86 ptrace side works
around it by constructing the enum just right to avoid a problem. In the
end there is no functional problem, but it is somewhat strange and
fragile.

It could also be improved like this [1], by better utilizing the smaller
array, but this still wastes space in the regset array’s if they are not
carefully crafted to avoid gaps. Instead, just fully separate out the
enums and give them separate 32 and 64 enum names. Add some bitsize-free
defines for REGSET_GENERAL and REGSET_FP since they are the only two
referred to in bitsize generic code.

While introducing a bunch of new 32/64 enums, change the pattern of the
name from REGSET_FOO32 to REGSET32_FOO to better indicate that the 32 is
in reference to the CPU mode and not the register size, as suggested by
Eric Biederman.

This should have no functional change and is only changing how constants
are generated and referred to.

[1] https://lore.kernel.org/lkml/20180717162502.32274-1-yu-cheng.yu@intel.com/Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/all/20221021221803.10910-2-rick.p.edgecombe%40intel.com