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

["Kewen.Lin" <linkw@linux.ibm.com>]

Hi Segher,

on 2022/9/1 23:04, Segher Boessenkool wrote:
> On Thu, Sep 01, 2022 at 05:05:44PM +0800, Kewen.Lin wrote:
>>> On Wed, Aug 31, 2022 at 05:33:28PM +0800, Kewen.Lin wrote:
>>> *Should* -mpowerpc64  be disabled by -m32?  
>>
>> I think the reason to disable -mpowerpc64 at -m32 is that we have
>> -mpowerpc64 explicitly specified at -m64 (equivalent behavior).
> 
> *Im*plicitly.  Explicit means the user has it on the command line.
> 

aha, let me reword it. :)  ... is that when -m64 is specified we make
it act like -mpowerpc64 is specified explicitly too even if user doesn't
actually specify -mpowerpc64.

>> In the current implementation, when -m64 is specified, we set the
>> bit OPTION_MASK_POWERPC64 in both opts and opts_set.  Since we
>> set OPTION_MASK_POWERPC64 in opts_set for -m64, when we find the
>> OPTION_MASK_POWERPC64 is ON in opts_set, we don't know if there
>> is one actual cmd-line option -mpowerpc64 or just -m64.
> 
> Yes.  That is what _explicit is for :-)
> 
>> Without any explicit -mpowerpc64 (and -mno-), I think we all agree
>> that -m64 should set OPTION_MASK_POWERPC64 in opts, conversely -m32
>> should unset OPTION_MASK_POWERPC64 in opts.
> 
> The latter only for OSes that do not handle -mpowerpc64 correctly.

I think it's the same for the OSes that handle -mpowerpc64 correctly.

Note that it's for the context without any explicit -mpowerpc64 (and
-mno-), assuming we don't "unset OPTION_MASK_POWERPC64 in opts" for
-m32, then the command line "-m64 -m32" would not be the same as
"-m32", since the previous "-m64" sets OPTION_MASK_POWERPC64 in opts
and it's still kept, it's unexpected.

> 
>> To make -m32/-m64 and -mpowerpc64 orthogonal, IMHO we should not
>> set bit OPTION_MASK_POWERPC64 in opts_set for -m64.
> 
> No.  Instead, we should not touch it if the user has explicitly set it
> or unset it.  Just like with all other flags :-)

I may miss something, but I think what we said here is consistent.
"should not set bit OPTION_MASK_POWERPC64 in opts_set" means we should
not make it act as -mpowerpc64 is specified explicitly, (once we won't
do the "unexpected" thing for -m64, then no reason to unset it for -m32
conversely, so explicit set/unset -mpowerpc64 is independent of -m32/-m64). 

BR,
Kewen