linux-kernel - Re: [RFC PATCH 1/5] elf: add livepatch-specific elf constants

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Date:	Thu, 12 Nov 2015 09:45:06 -0600
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Jessica Yu <jeyu@...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: [RFC PATCH 1/5] elf: add livepatch-specific elf constants

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.

>  /* 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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