Re: [PATCH v3 7/7] powerpc64le: Enable float128

[Florian Weimer <fw at deneb dot enyo dot de>]

* Peter Bergner:

> On 6/27/17 2:17 PM, Florian Weimer wrote:
>> * Peter Bergner:
>>> bergner@pike:~$ cat float128.c
>>> int
>>> float128 (void)
>>> {
>>>   return __builtin_cpu_supports ("ieee128");
>>> }
>>> bergner@pike:~$ gcc -O2 -S float128.c
>>> bergner@pike:~$ cat float128.s
>>> 	[snip]
>>> float128:
>>> 	lwz 3,-28776(13)
>>> 	rldicl 3,3,42,63
>>> 	blr
>> 
>> Nice.  I guess the next question is: what would ensure that this code
>> only runs on a glibc which sets up the TCB in the expected way?  Is
>> there a symbol reference which prevents that?
>> 
>> __parse_hwcap_and_convert_at_platform isn't that symbol, as far as I
>> can tell.
>
> Yes, we emit a symbol only defined by libcs that support this and
> yes, __parse_hwcap_and_convert_at_platform is that symbol:
>
>   if (cpu_builtin_p)
>     {
>       /* We have expanded a CPU builtin, so we need to emit a reference to
>          the special symbol that LIBC uses to declare it supports the
>          AT_PLATFORM and AT_HWCAP/AT_HWCAP2 in the TCB feature.  */
>       switch_to_section (data_section);
>       fprintf (asm_out_file, "\t.align %u\n", TARGET_32BIT ? 2 : 3);
>       fprintf (asm_out_file, "\t%s %s\n",
>                TARGET_32BIT ? ".long" : ".quad", tcb_verification_symbol);
>     }

I see, so everything is fine.  Nice!