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Documentation: livepatch: add section about arch-specific code

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Document usage of arch-specific elf sections in livepatch as well
as implementation of arch-specific code.

[jkosina@suse.cz: fix wording as suggested by Petr Mladek]
Signed-off-by: Jessica Yu <jeyu@redhat.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
This commit is contained in:
Jessica Yu 2016-08-17 20:58:30 -04:00 committed by Jiri Kosina
parent d4c3e6e1b1
commit 5ad75fcdd7
1 changed files with 16 additions and 4 deletions
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20
Documentation/livepatch/module-elf-format.txt
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@ -25,7 +25,8 @@ Table of Contents
3.3.2 Required name format
3.3.3 Example livepatch symbol names
3.3.4 Example `readelf --symbols` output
4. Symbol table and Elf section access
4. Architecture-specific sections
5. Symbol table and Elf section access
----------------------------
0. Background and motivation
@ -46,7 +47,7 @@ architecture.
Since apply_relocate_add() requires access to a module's section header
table, symbol table, and relocation section indices, Elf information is
preserved for livepatch modules (see section 4). Livepatch manages its own
preserved for livepatch modules (see section 5). Livepatch manages its own
relocation sections and symbols, which are described in this document. The
Elf constants used to mark livepatch symbols and relocation sections were
selected from OS-specific ranges according to the definitions from glibc.
@ -117,7 +118,7 @@ also possible for a livepatch module to have no livepatch relocation
sections, as in the case of the sample livepatch module (see
samples/livepatch).
Since Elf information is preserved for livepatch modules (see Section 4), a
Since Elf information is preserved for livepatch modules (see Section 5), a
livepatch relocation section can be applied simply by passing in the
appropriate section index to apply_relocate_add(), which then uses it to
access the relocation section and apply the relocations.
@ -292,8 +293,19 @@ Symbol table '.symtab' contains 127 entries:
[*] Note that the 'Ndx' (Section index) for these symbols is SHN_LIVEPATCH (0xff20).
"OS" means OS-specific.
---------------------------------
4. Architecture-specific sections
---------------------------------
Architectures may override arch_klp_init_object_loaded() to perform
additional arch-specific tasks when a target module loads, such as applying
arch-specific sections. On x86 for example, we must apply per-object
.altinstructions and .parainstructions sections when a target module loads.
These sections must be prefixed with ".klp.arch.$objname." so that they can
be easily identified when iterating through a patch module's Elf sections
(See arch/x86/kernel/livepatch.c for a complete example).
--------------------------------------
4. Symbol table and Elf section access
5. Symbol table and Elf section access
--------------------------------------
A livepatch module's symbol table is accessible through module->symtab.