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

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Message-ID: <555CEF45.4090609@zytor.com>
Date:	Wed, 20 May 2015 13:32:05 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...capital.net>,
	"H.J. Lu" <hjl.tools@...il.com>
CC:	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 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?

	-hpa


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