Re: [PATCH] rs6000/test: Fix bswap64-4.c with has_arch_ppc64 [PR106680]

[Peter Bergner <bergner@linux.ibm.com>]

On 8/31/22 4:07 PM, Segher Boessenkool wrote:
> On Wed, Aug 31, 2022 at 02:53:07PM -0500, Peter Bergner wrote:
>> Changing OS_MISSING_POWERPC64 as I mentioned would not add OPTION_MASK_POWERPC64
>> to our cpu masks when -m32 is used.
> 
> So you say this is where the bug is?

For linux64.h which is what I think the powerpc64-linux build will use,
we have:

linux64.h:#define OS_MISSING_POWERPC64 !TARGET_64BIT

Doing the macro expansion by hand into:

  set_masks = POWERPC_MASKS;
#ifdef OS_MISSING_POWERPC64
  if (OS_MISSING_POWERPC64)
    set_masks &= ~OPTION_MASK_POWERPC64;
#endif


...gives us:

  set_masks = POWERPC_MASKS;
  if (!TARGET_64BIT)
    set_masks &= ~OPTION_MASK_POWERPC64;

So if we handled a -mpowerpc64 earlier on the command line and added
OPTION_MASK_POWERPC64 to our cpu mask, then a following -m32 use will
remove it here.

So I mentioned doing:

linux64.h:
- #define OS_MISSING_POWERPC64 !TARGET_64BIT
+ #define OS_MISSING_POWERPC64 0

...which disables the above code only for powerpc64-linux builds and doesn't
affect AIX, Darwin, BSD, etc. or a powerpc-linux build.


> The kernel has.  But there are user space things (glibc) that haven't
> been fixed, and those are default as well.

Sure, but someone who is using -m32 -mpowerpc64 should know that and
relying on a 32-bit glibc to save/restore the full 64-bit registers
is a user error in my book.  If you're using -m32 -mpower64, you
better know what you are doing and the limitations you have to live under.



Peter