Re: Documentation: livepatch: add section about arch-specific code

[Jessica Yu]

+++ Petr Mladek [18/08/16 11:57 +0200]:
> On Wed 2016-08-17 20:58:30, Jessica Yu wrote:
> > Document usage of arch-specific elf sections in livepatch as well
> > as implementation of arch-specific code.
> >
> > Signed-off-by: Jessica Yu <jeyu@xxxxxxxxxx>
> > ---
> >  Documentation/livepatch/module-elf-format.txt | 20 ++++++++++++++++----
> >  1 file changed, 16 insertions(+), 4 deletions(-)
> >
> > diff --git a/Documentation/livepatch/module-elf-format.txt b/Documentation/livepatch/module-elf-format.txt
> > index eedbdcf..02bfafa 100644
> > --- a/Documentation/livepatch/module-elf-format.txt
> > +++ b/Documentation/livepatch/module-elf-format.txt
> > @@ -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 can be prefixed with ".klp.arch.$objname." so that they can
>                  ^^^
>
> I would personally use "must" instead of "can". Or replace "can be prefixed"
> with "are prefixed".

Agreed, poor word choice there. Let's just swap "can" with "must."

Jessica