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

[Richard Earnshaw <rearnsha@arm.com>]

[-- Attachment #1: Type: text/plain, Size: 3852 bytes --]

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.

R.

[-- Attachment #2: hard-float-dyn.patch --]
[-- Type: text/plain, Size: 1630 bytes --]

--- linux-eabi.h	(revision 186924)
+++ linux-eabi.h	(local)
@@ -32,7 +32,8 @@
   while (false)
 
 /* We default to a soft-float ABI so that binaries can run on all
-   target hardware.  */
+   target hardware.  If you override this to use the hard-float ABI then
+   change the setting of GLIBC_DYNAMIC_LINKER_DEFAULT as well.  */
 #undef  TARGET_DEFAULT_FLOAT_ABI
 #define TARGET_DEFAULT_FLOAT_ABI ARM_FLOAT_ABI_SOFT
 
@@ -59,16 +60,19 @@
 #undef  SUBTARGET_EXTRA_LINK_SPEC
 #define SUBTARGET_EXTRA_LINK_SPEC " -m " TARGET_LINKER_EMULATION
 
-/* Use ld-linux.so.3 so that it will be possible to run "classic"
-   GNU/Linux binaries on an EABI system.  */
+/* GNU/Linux on ARM currently supports three dynamic linkers:
+   - ld-linux.so.2 - for the legacy ABI
+   - ld-linux.so.3 - for the EABI-derived soft-float ABI
+   - ld-linux-armhf.so.3 - for the EABI-derived hard-float ABI.
+   All the dynamic linkers live in /lib.
+   We default to soft-float, but this can be overridden by changing both
+   GLIBC_DYNAMIC_LINKER_DEFAULT and TARGET_DEFAULT_FLOAT_ABI.  */
+
 #undef  GLIBC_DYNAMIC_LINKER
 #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 "} \