linux-kernel - Re: elf: add livepatch-specific elf constants

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Message-ID: <20151113064951.GD13513@packer-debian-8-amd64.digitalocean.com>
Date:	Fri, 13 Nov 2015 01:49:51 -0500
From:	Jessica Yu <jeyu@...hat.com>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Seth Jennings <sjenning@...hat.com>,
	Jiri Kosina <jikos@...nel.org>,
	Vojtech Pavlik <vojtech@...e.com>,
	Miroslav Benes <mbenes@...e.cz>, linux-api@...r.kernel.org,
	live-patching@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: elf: add livepatch-specific elf constants

+++ Josh Poimboeuf [12/11/15 09:45 -0600]:
>On Mon, Nov 09, 2015 at 11:45:51PM -0500, Jessica Yu wrote:
>> Add livepatch elf reloc section flag, livepatch symbol bind
>> and section index
>>
>> Signed-off-by: Jessica Yu <jeyu@...hat.com>
>> ---
>>  include/uapi/linux/elf.h | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
>> index 71e1d0e..967ce1b 100644
>> --- a/include/uapi/linux/elf.h
>> +++ b/include/uapi/linux/elf.h
>> @@ -118,6 +118,7 @@ typedef __s64	Elf64_Sxword;
>>  #define STB_LOCAL  0
>>  #define STB_GLOBAL 1
>>  #define STB_WEAK   2
>> +#define STB_LIVEPATCH_EXT 11
>>
>>  #define STT_NOTYPE  0
>>  #define STT_OBJECT  1
>> @@ -286,6 +287,7 @@ typedef struct elf64_phdr {
>>  #define SHF_ALLOC	0x2
>>  #define SHF_EXECINSTR	0x4
>>  #define SHF_MASKPROC	0xf0000000
>> +#define SHF_RELA_LIVEPATCH  0x4000000
>
>Writing the value with leading zeros (0x04000000) would it more
>readable.
>
>Also the OS-specific range mask (SHF_MASKOS) is 0x0ff00000.  Any reason
>you went with 0x04000000 as opposed to the first value in the range
>(0x00100000)?  I don't see anybody else using that value.

I don't have any particular reason, I think I just picked any value
and ran with it. I'll just change it to the first value in the range
since that makes more sense.

>>  /* special section indexes */
>>  #define SHN_UNDEF	0
>> @@ -295,6 +297,7 @@ typedef struct elf64_phdr {
>>  #define SHN_ABS		0xfff1
>>  #define SHN_COMMON	0xfff2
>>  #define SHN_HIRESERVE	0xffff
>> +#define SHN_LIVEPATCH 0xff21
>
>Similar question here, why not use 0xff20 (SHN_LOOS)?
>
>-- 
>Josh
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