Re: [AArch64/wwwdoc] Document -fpic support for small memory model

[Jiong Wang <jiong dot wang at arm dot com>]

James Greenhalgh writes:

> On Fri, Jun 26, 2015 at 02:45:39PM +0100, Jiong Wang wrote:
>> 
>> Marcus Shawcroft writes:
>> 
>> 2015-06-26  Jiong Wang  <jiong.wang@arm.com>
>> 
>> wwwdocs/
>>   * htdocs/gcc-6/changes.html (AArch64): Document -fpic for small model.
>> 
>
>> Index: gcc-6/changes.html
>> ===================================================================
>> RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-6/changes.html,v
>> retrieving revision 1.12
>> diff -u -r1.12 changes.html
>> --- gcc-6/changes.html	16 Jun 2015 08:48:02 -0000	1.12
>> +++ gcc-6/changes.html	26 Jun 2015 13:30:05 -0000
>> @@ -90,6 +90,15 @@
>>         If GCC is unable to detect the host CPU these options have no effect.
>>       </li>
>>     </ul>
>> +   <ul>
>
> This should be a new <li> (list item) in the above <ul> (unordered list),
> rather than a new <ul>.

thanks, fixed.

>
>> +     <li>
>> +       <code>-fpic</code> is now supported on AArch64 for small memory
>> +       model. 
>
> In invoke.texi we describe -mcmodel as the "small code model" rather
> than as a "memory model". How about rewording this as so:
>
>   <code>-fpic</code> is now supported by the AArch64 target when generating
>   code for the small code model (<code>-mcmodel=small</code>).

fixed.

>
>> Compared with <code>-fPIC</code>, <code>-fpic</code>
>> +       will guide GCC to generate more efficient position independent
>> +       instruction sequences when accessing global objects and
>> +       28KiB/15KiB global offset table size supported under ILP64/32.
>
> I'm not sure this part is needed, the difference between -fpic and -fPIC
> is already covered by invoke.texi. If you do want to include this text,
> I might try rewriting it as:
>
>   <code>-fpic</code> generates position-independent code which accesses all
>   constant addresses through a global offset table (GOT). For AArch64, the
>   size of the GOT is limited to 28KiB under the LP64 SysV ABI, and 15KiB
>   under the ILP32 SysV ABI.

As this page documents changes, I combined two of your rewording together as:

  <code>-fpic</code> is now supported by the AArch64 target when generating
  code for the small code model (<code>-mcmodel=small</code>).  The size of
  the GOT is limited to 28KiB under the LP64 SysV ABI, and 15KiB under the
  ILP32 SysV ABI.
  
>
> As I was looking in invoke.texi, do we want to document the limits on our
> GOT size there as other targets have?

Maybe, I haven't touch invoke.texi in this patch.

>
> "These maximums are 8k on the SPARC and 32k on the m68k and RS/6000.
>  The x86 has no such limit."

patch updated. Ok for trunk?

2015-07-23  Jiong Wang  <jiong.wang@arm.com>
 
wwwdocs/
  * htdocs/gcc-6/changes.html (AArch64): Document -fpic for small model.

-- 
Regards,
Jiong

Index: htdocs/gcc-6/changes.html
===================================================================
RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-6/changes.html,v
retrieving revision 1.12
diff -u -r1.12 changes.html
--- htdocs/gcc-6/changes.html	16 Jun 2015 08:48:02 -0000	1.12
+++ htdocs/gcc-6/changes.html	23 Jul 2015 08:45:11 -0000
@@ -89,6 +89,12 @@
        rewrite these options to the optimal setting for that system.
        If GCC is unable to detect the host CPU these options have no effect.
      </li>
+     <li>
+       <code>-fpic</code> is now supported by the AArch64 target when generating
+       code for the small code model (<code>-mcmodel=small</code>).  The size of
+       the GOT is limited to 28KiB under the LP64 SysV ABI, and 15KiB under the
+       ILP32 SysV ABI.
+     </li>
    </ul>
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