linux-kernel - Re: RFC: Add -mshared option to x86 ELF assembler

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Date:	Wed, 20 May 2015 13:54:01 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"H.J. Lu" <hjl.tools@...il.com>, Jan Beulich <JBeulich@...e.com>,
	Binutils <binutils@...rceware.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: RFC: Add -mshared option to x86 ELF assembler

On Wed, May 20, 2015 at 1:32 PM, H. Peter Anvin <hpa@...or.com> wrote:
> On 05/20/2015 01:02 PM, Andy Lutomirski wrote:
>>>
>>> I got
>>>
>>> [hjl@...-tools-1 kernel.org]$ readelf -r old/vmlinux.o | head -5
>>>
>>> Relocation section '.rela.text' at offset 0xafea2f0 contains 205717 entries:
>>>   Offset          Info           Type           Sym. Value    Sym. Name + Addend
>>> 000000000001  1253100000002 R_X86_64_PC32     0000000000001e70 __fentry__ - 4
>>> 000000000009  1c8c00000002 R_X86_64_PC32     0000000000000000 .data + 51bc
>>> [hjl@...-tools-1 kernel.org]$ readelf -r new/vmlinux.o | head -5
>>>
>>> Relocation section '.rela.text' at offset 0xafea280 contains 205711 entries:
>>>   Offset          Info           Type           Sym. Value    Sym. Name + Addend
>>> 000000000001  1253100000002 R_X86_64_PC32     0000000000001e70 __fentry__ - 4
>>> 000000000009  1c8c00000002 R_X86_64_PC32     0000000000000000 .data + 51bc
>>> [hjl@...-tools-1 kernel.org]$
>>>
>>> It removes 6 relocations.  On gcc master branch,
>>>
>>> [hjl@...-tools-1 gcc-misc]$ size build-x86_64-linux*/gcc/cc1
>>>    text   data    bss    dec    hex filename
>>> 21529621  62256 1348312 22940189 15e0a1d build-x86_64-linux.branch/gcc/cc1
>>> 21529749  62256 1348312 22940317 15e0a9d build-x86_64-linux/gcc/cc1
>>> [hjl@...-tools-1 gcc-misc]$ size build-x86_64-linux*/gcc/cc1plus
>>>    text   data    bss    dec    hex filename
>>> 23713509  62400 1372760 25148669 17fbcfd build-x86_64-linux.branch/gcc/cc1plus
>>> 23713669  62400 1372760 25148829 17fbd9d build-x86_64-linux/gcc/cc1plus
>>> [hjl@...-tools-1 gcc-misc]$
>>>
>>> It is more effective.  I will run more tests.
>>
>> This seems like a sensible idea, but I can imagine it breaking some
>> weird use cases (like that one Linux thing).  Is that okay?
>>
>
> What about the patch I posted recently?
>

I replied in that thread.

--Andy

>         -hpa
>
>



-- 
Andy Lutomirski
AMA Capital Management, LLC
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