linux-kernel - [RFC PATCH v2 1/6] Elf: add livepatch-specific Elf constants

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Date:	Mon, 30 Nov 2015 23:21:14 -0500
From:	Jessica Yu <jeyu@...hat.com>
To:	Rusty Russell <rusty@...tcorp.com.au>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Seth Jennings <sjenning@...hat.com>,
	Jiri Kosina <jikos@...nel.org>,
	Vojtech Pavlik <vojtech@...e.com>,
	Jonathan Corbet <corbet@....net>,
	Miroslav Benes <mbenes@...e.cz>
Cc:	linux-api@...r.kernel.org, live-patching@...r.kernel.org,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	linux-s390@...r.kernel.org, linux-doc@...r.kernel.org
Subject: [RFC PATCH v2 1/6] Elf: add livepatch-specific Elf constants

Add livepatch Elf relocation section flag (SHF_RELA_LIVEPATCH), livepatch
symbol bind (STB_LIVEPATCH_EXT) and section index (SHN_LIVEPATCH).
The values of these Elf constants were selected from OS-specific ranges
according to the definitions from glibc.

Livepatch relocation sections are marked with SHF_RELA_LIVEPATCH to
indicate to the module loader that it should not apply that relocation
section and that livepatch will handle them.

The SHN_LIVEPATCH shndx marks symbols that will be resolved by livepatch.
The module loader ignores these symbols and does not attempt to resolve
them.

The STB_LIVEPATCH_EXT symbol bind marks the scope of certain livepatch
symbols, so that livepatch can appropriately resolve them.

Signed-off-by: Jessica Yu <jeyu@...hat.com>
---
 include/uapi/linux/elf.h | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
index 71e1d0e..95ff318 100644
--- a/include/uapi/linux/elf.h
+++ b/include/uapi/linux/elf.h
@@ -115,9 +115,10 @@ typedef __s64	Elf64_Sxword;
 #define DT_HIPROC	0x7fffffff
 
 /* This info is needed when parsing the symbol table */
-#define STB_LOCAL  0
-#define STB_GLOBAL 1
-#define STB_WEAK   2
+#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
@@ -282,16 +283,18 @@ typedef struct elf64_phdr {
 #define SHT_HIUSER	0xffffffff
 
 /* sh_flags */
-#define SHF_WRITE	0x1
-#define SHF_ALLOC	0x2
-#define SHF_EXECINSTR	0x4
-#define SHF_MASKPROC	0xf0000000
+#define SHF_WRITE		0x1
+#define SHF_ALLOC		0x2
+#define SHF_EXECINSTR		0x4
+#define SHF_RELA_LIVEPATCH	0x00100000
+#define SHF_MASKPROC		0xf0000000
 
 /* special section indexes */
 #define SHN_UNDEF	0
 #define SHN_LORESERVE	0xff00
 #define SHN_LOPROC	0xff00
 #define SHN_HIPROC	0xff1f
+#define SHN_LIVEPATCH	0xff20
 #define SHN_ABS		0xfff1
 #define SHN_COMMON	0xfff2
 #define SHN_HIRESERVE	0xffff
-- 
2.4.3

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