Re: [PATCH v2] ARM: Use different linker path for hardfloat ABI

[Michael Hope <michael.hope@linaro.org>]

On 1 May 2012 03:24, Richard Earnshaw <rearnsha@arm.com> wrote:
> On 27/04/12 00:27, Michael Hope wrote:
>> On 27 April 2012 08:20, Carlos O'Donell <carlos@systemhalted.org> wrote:
>>> On Mon, Apr 23, 2012 at 5:36 PM, Michael Hope <michael.hope@linaro.org> wrote:
>>>> 2012-04-24  Michael Hope  <michael.hope@linaro.org>
>>>>            Richard Earnshaw  <rearnsha@arm.com>
>>>>
>>>>        * config/arm/linux-eabi.h (GLIBC_DYNAMIC_LINKER_SOFT_FLOAT): Define.
>>>>        (GLIBC_DYNAMIC_LINKER_HARD_FLOAT): Define.
>>>>        (GLIBC_DYNAMIC_LINKER_DEFAULT): Define.
>>>>        (GLIBC_DYNAMIC_LINKER): Redefine to use the hard float path.
>>>>
>>>> diff --git a/gcc/config/arm/linux-eabi.h b/gcc/config/arm/linux-eabi.h
>>>> index 80bd825..2ace6f0 100644
>>>> --- a/gcc/config/arm/linux-eabi.h
>>>> +++ b/gcc/config/arm/linux-eabi.h
>>>> @@ -62,7 +62,17 @@
>>>>  /* Use ld-linux.so.3 so that it will be possible to run "classic"
>>>>    GNU/Linux binaries on an EABI system.  */
>>>>  #undef  GLIBC_DYNAMIC_LINKER
>>>> -#define GLIBC_DYNAMIC_LINKER "/lib/ld-linux.so.3"
>>>> +#define GLIBC_DYNAMIC_LINKER_SOFT_FLOAT "/lib/ld-linux.so.3"
>>>> +#define GLIBC_DYNAMIC_LINKER_HARD_FLOAT "/lib/ld-linux-armhf.so.3"
>>>> +#if TARGET_DEFAULT_FLOAT_ABI == ARM_FLOAT_ABI_HARD
>>>> +#define GLIBC_DYNAMIC_LINKER_DEFAULT GLIBC_DYNAMIC_LINKER_HARD_FLOAT
>>>> +#else
>>>> +#define GLIBC_DYNAMIC_LINKER_DEFAULT GLIBC_DYNAMIC_LINKER_SOFT_FLOAT
>>>> +#endif
>>>> +#define GLIBC_DYNAMIC_LINKER \
>>>> +   "%{mfloat-abi=hard:" GLIBC_DYNAMIC_LINKER_HARD_FLOAT "} \
>>>> +    %{mfloat-abi=soft*:" GLIBC_DYNAMIC_LINKER_SOFT_FLOAT "} \
>>>> +    %{!mfloat-abi=*:" GLIBC_DYNAMIC_LINKER_DEFAULT "}"
>>>>
>>>>  /* At this point, bpabi.h will have clobbered LINK_SPEC.  We want to
>>>>    use the GNU/Linux version, not the generic BPABI version.  */
>>>
>>> This patch is broken. Please fix this.
>>>
>>> You can't use a named enumeration in cpp equality.
>>>
>>> The type ARM_FLOAT_ABI_HARD is a named enumeration and evaluates to 0
>>> as an unknown identifier.
>>>
>>> Therefore "#if TARGET_DEFAULT_FLOAT_ABI == ARM_FLOAT_ABI_HARD"
>>> evaluates to "#if 0 == 0" and is always true.
>>>
>>> Watch out that "#define ARM_FLOAT_ABI_HARD ARM_FLOAT_ABI_HARD" for
>>> such enums is not conforming C99/C11.
>>>
>>> I suggest you define the types as macros and then set the named enum
>>> to those values, then use the macros in the header equality checks.
>>>
>>> e.g.
>>> #define VAL1 0 then enum FOO { RVAL1 = VAL1, ... }
>>>
>>> Look at arm.h for the enum definition.
>>
>> I've looked further into this and I think the original pre-#if version
>> is correct.
>>
>> The float ABI comes from these places:
>>  * The -mfloat-abi= command line argument, else
>>  * The --with-float= configure time argument, else
>>  * TARGET_DEFAULT_FLOAT_ABI from linux-eabi.h
>>
>> In the first case the ABI is explicit.  In the second
>> OPTION_DEFAULT_SPECS turns the configure time argument into an explict
>> -mfloat-abi=.
>>
>> The patch below covers all cases, keeps the logic in the spec file,
>> and adds a comment linking the two #defines.
>>
>> Tested by building with no configure flags, --wtih-float=softfp,
>> --with-float=hard, and then running with all combinations of
>> {,-mfloat-abi=softfp,-mfloat-abi=hard} {,-mglibc,-muclibc,-mbionic}.
>>
>> OK?
>>
>> -- Michael
>>
>> 2012-04-27  Michael Hope  <michael.hope@linaro.org>
>>
>>       * config/arm/linux-eabi.h (GLIBC_DYNAMIC_LINKER): Pick the loader
>>       using a spec rule.
>>
>
> Michael,
>
> can you try this patch please.  It should make it possible to then
> create linux-eabihf.h containing just
>
> #undef TARGET_DEFAULT_FLOAT_ABI
> #define TARGET_DEFAULT_FLOAT_ABI ARM_FLOAT_ABI_HARD
> #undef GLIBC_DYNAMIC_LINKER_DEFAULT
> #define GLIBC_DYNAMIC_LINKER_DEFAULT GLIBC_DYNAMIC_LINKER_HARD_FLOAT
>
> Which is not quite as simple as leaving out the second re-define, but
> pretty close.

Hi Richard.  Your patch tests just fine.  I like it.  You could change
the spec rule to the newer if-elseif-else form but that's a nit.

-- Michael