Re: module: preserve Elf information for livepatch modules

[Jessica Yu]

+++ Josh Poimboeuf [08/02/16 14:10 -0600]:
> On Wed, Feb 03, 2016 at 08:11:07PM -0500, Jessica Yu wrote:
> > For livepatch modules, copy Elf section, symbol, and string information
> > from the load_info struct in the module loader. Persist copies of the
> > original symbol table and string table.
> >
> > Livepatch manages its own relocation sections in order to reuse module
> > loader code to write relocations. Livepatch modules must preserve Elf
> > information such as section indices in order to apply livepatch relocation
> > sections using the module loader's apply_relocate_add() function.
> >
> > In order to apply livepatch relocation sections, livepatch modules must
> > keep a complete copy of their original symbol table in memory. Normally, a
> > stripped down copy of a module's symbol table (containing only "core"
> > symbols) is made available through module->core_symtab. But for livepatch
> > modules, the symbol table copied into memory on module load must be exactly
> > the same as the symbol table produced when the patch module was compiled.
> > This is because the relocations in each livepatch relocation section refer
> > to their respective symbols with their symbol indices, and the original
> > symbol indices (and thus the symtab ordering) must be preserved in order
> > for apply_relocate_add() to find the right symbol.
>
> This patch didn't apply clean to linux-next/master.  I didn't
> investigate why, but maybe it depends on the other patch set which
> removes the notifiers?  (If so, that should be mentioned in the cover
> letter.)

A very recent commit (8244062ef) introduced some changes
kernel/module.c that intersect with this patch, so I think this is why
the patch didn't apply cleanly to today's tree...Anyhow I will rebase
again before sending out v5. Thanks for the comments :-)

Jessica