Re: Fwd: [PATCH, ARM]An accurate way to calculate the target arch attribute

[Richard Earnshaw <rearnsha at arm dot com>]

On 19/11/14 10:33, Terry Guo wrote:
> 
> 
>> -----Original Message-----
>> From: binutils-owner@sourceware.org [mailto:binutils-
>> owner@sourceware.org] On Behalf Of Richard Earnshaw
>> Sent: Wednesday, November 19, 2014 6:16 PM
>> To: Terry Guo; binutils@sourceware.org
>> Subject: Re: Fwd: [PATCH, ARM]An accurate way to calculate the target arch
>> attribute
>>
>> On 29/09/14 04:10, Terry Guo wrote:
>>> Hi there,
>>>
>>> When target isn't specified from either command line or .arch/.cpu
>>> directive, current gas will calculate the target arch before
>>> relaxation step and assume that a possible relaxation will happen
>>> anyway even this relaxation doesn't happen in late relaxation step.
>>> This causes a overly assumption to target arch e.g. set target arch to
>>> armv6t2 where armv4t is good enough.
>>>
>>> The attached patch intends to do an accurate calculation of target
>>> arch by considering the target arch in relaxation step.
>>>
>>> Tested with Binutils regression test. Is it OK?
>>>
>>> BR,
>>> Terry
>>>
>>> gas/
>>> 2014-09-29  Terry Guo  <terry.guo@arm.com>
>>>
>>>           * config/tc-arm.c (md_assemble): Do not consider relaxation.
>>>           (md_convert_frag): Test and set target arch attribute
> accordingly.
>>>           (aeabi_set_attribute_string): Turn it into a global function.
>>>           * config/tc-arm.h (md_post_relax_hook): Enable it for ARM
> target.
>>>           (aeabi_set_public_attributes): Declare it.
>>>
>>> gas/testsuite/
>>> 2014-09-29  Terry Guo  <terry.guo@arm.com>
>>>
>>>           * gas/arm/attr-arch-assumption.d: New file.
>>>           * gas/arm/attr-arch-assumption.s: Likewise.
>>>
>>
>> These bits seem essentially OK, but ...
>>
>>> ld/testsuite/
>>> 2014-09-29  Terry Guo  <terry.guo@arm.com>
>>>
>>>           * ld-arm/tls-longplt-lib.d: Updated.
>>>           * ld-arm/tls-longplt-lib.s: Likewise.
>>>           * ld-arm/tls-longplt.d: Likewise.
>>>           * ld-arm/tls-longplt.s: Likewise.
>>
>> Why is this needed?  This code doesn't look like it needs to assume v6t2
> as a
>> baseline.
>>
>> R.
> 
> Thanks for review. Before my patch, the target arch for those .s files are
> calculated in an inaccurate way, the armv6t2 is assumed here. Hence the
> content of .d files are for armv6t2. Now with my patch, the arch for those
> files are calculated in an accurate way, the armv4t is assumed here, so the
> existing .d files can't be matched. There are two ways to avoid such
> mismatch, one is to explicitly set arch to armv6t2 in .s files, then no need
> to change the .d files. Another is to update the .d files without touching
> the .s files. Which way is better in your opinion?
> 

Except that you do end up modifying the .d files since the NOP opcode
used is different.  So what else changes if you don't set the architecture?


> BR,
> Terry
> 
>