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

[Richard Earnshaw <rearnsha at arm dot com>]

On 03/04/12 11:51, Richard Guenther wrote:
> On Tue, Apr 3, 2012 at 12:45 PM, Richard Earnshaw <rearnsha@arm.com> wrote:
>> On 03/04/12 10:29, Andrew Haley wrote:
>>> On 04/02/2012 10:06 PM, dann frazier wrote:
>>>> On Fri, Mar 30, 2012 at 06:52:34PM +0100, Richard Earnshaw wrote:
>>>>> On 29/03/12 20:34, dann frazier wrote:
>>>>>> This is an updated version of a patch Debian and Ubuntu are using to
>>>>>> use an alternate linker path for hardfloat binaries. The difference
>>>>>> with this one is that it covers the case where no float flag
>>>>>> was passed in, defaulting to the softfloat path.
>>>>>>
>>>>>> 2012-03-29  dann frazier <dann.frazier@canonical.com>
>>>>>>
>>>>>>    * config/arm/linux-elf.h: Use alternate linker path
>>>>>>           for hardfloat ABI
>>>>>>
>>>>>> Index: gcc/config/arm/linux-elf.h
>>>>>> ===================================================================
>>>>>> --- gcc/config/arm/linux-elf.h     (revision 185708)
>>>>>> +++ gcc/config/arm/linux-elf.h     (working copy)
>>>>>> @@ -59,14 +59,21 @@
>>>>>>
>>>>>>  #define LIBGCC_SPEC "%{mfloat-abi=soft*:-lfloat} -lgcc"
>>>>>>
>>>>>> -#define GLIBC_DYNAMIC_LINKER "/lib/ld-linux.so.2"
>>>>>> +#define LINUX_DYNAMIC_LINKER_SF "/lib/ld-linux.so.3"
>>>>>> +#define LINUX_DYNAMIC_LINKER_HF "/lib/arm-linux-gnueabihf/ld-linux.so.3"
>>>>>>
>>>>>>  #define LINUX_TARGET_LINK_SPEC  "%{h*} \
>>>>>>     %{static:-Bstatic} \
>>>>>>     %{shared:-shared} \
>>>>>>     %{symbolic:-Bsymbolic} \
>>>>>>     %{rdynamic:-export-dynamic} \
>>>>>> -   -dynamic-linker " GNU_USER_DYNAMIC_LINKER " \
>>>>>> +   %{msoft-float:-dynamic-linker " LINUX_DYNAMIC_LINKER_SF "} \
>>>>>> +   %{mfloat-abi=soft*:-dynamic-linker " LINUX_DYNAMIC_LINKER_SF "} \
>>>>>> +   %{mhard-float:-dynamic-linker " LINUX_DYNAMIC_LINKER_HF "} \
>>>>>> +   %{mfloat-abi=hard:-dynamic-linker " LINUX_DYNAMIC_LINKER_HF "} \
>>>>>> +   %{!mfloat-abi: \
>>>>>> +     %{!msoft-float: \
>>>>>> +       %{!mhard-float:-dynamic-linker " LINUX_DYNAMIC_LINKER_SF "}}} \
>>>>>>     -X \
>>>>>>     %{mbig-endian:-EB} %{mlittle-endian:-EL}" \
>>>>>>     SUBTARGET_EXTRA_LINK_SPEC
>>>>>>
>>>>>
>>>>> Looks to me as though this will break the old Linux ABI.  While we've
>>>>> marked that as deprecated, it hasn't been removed as yet.  So I think
>>>>> this patch either needs to wait until that removal has taken place, or
>>>>> provide the relevant updates to maintain the old ABI support.
>>>>
>>>> Thanks for your review. You're right, this does appear to break the
>>>> old ABI - that was a misunderstanding on my part. I think this fixes
>>>> the problem:
>>>
>>> But what about those of us who are using hard-float but not the
>>> Debian liker path?  It'll break, surely.  This looks to be like
>>> it's Debian-specific.
>>>
>>
>> Are you trying to tell me that some distros are using /lib/ld-linux.so.3
>> directly for hard-float?  Sigh, you distro guys need to start talking to
>> each other, rather than just going of inventing things ...
>>
>> If, so then there's only one way to sort out this mess.
>>
>> /lib/arm-linux-gnueabi/ld-linux.so.3  Location of soft-float loader
>> /lib/arm-linux-gnueabihf/ld-linux.so.3 Location of hard-float loader
>> /lib/ld-linux.so.3 legacy symlink to one of the above.
>>
>> Or something of this nature.
>>
>> All this is outside of GCC's remit though and I'm not in a position to
>> drive any of it through.
>>
>> :-( :-( :-(
> 
> Now, I wonder why the dynamic linker cannot figure out the ABI itself
> by means of using ELF flags or so?
> 

There are no ELF flags for this in executables.  The attributes only
apply to object files and anyway they are too expensive to decode at run
time.

R.