On Fri, Mar 01, 2019 at 11:13:13AM -0300, Joao Moreira wrote: > Add a section to Documentation/livepatch/module-elf-format.txt > describing how klp-convert works for fixing relocations. > > Signed-off-by: Joao Moreira <jmoreira@xxxxxxx> > --- > Documentation/livepatch/module-elf-format.txt | 47 ++++++++++++++++++++++++--- > 1 file changed, 42 insertions(+), 5 deletions(-) > > diff --git a/Documentation/livepatch/module-elf-format.txt b/Documentation/livepatch/module-elf-format.txt > index f21a5289a09c..6b0259dfab49 100644 > --- a/Documentation/livepatch/module-elf-format.txt > +++ b/Documentation/livepatch/module-elf-format.txt > @@ -2,7 +2,8 @@ > Livepatch module Elf format > =========================== > > [ ... snip ... ] > > +-------------------------------------------------- > +4. Automatic conversion of unresolved relocations > +-------------------------------------------------- > +Sometimes livepatches may operate on symbols which are not self-contained nor > +exported. When this happens, these symbols remain unresolved in the elf object > +and will trigger an error during the livepatch instantiation. > + > +Whenever possible, the kernel building infrastructure solves this problem > +automatically. First, a symbol database containing information on all compiled > +objects is built. Second, this database - a file named Symbols.list, placed in > +the kernel source root directory - is used to identify targets for unresolved > +relocations, converting them in the livepatch elf accordingly to the > +specifications above-described. While the first staged is fully handled by the ^^^^^^ nit: s/staged/stage > +building system, the second is done by a tool called klp-convert, which can be > +found in "scripts/livepatch". > + > +When an unresolved relocation has as target a symbol whose name is also used by > +different symbols throughout the kernel, the relocation cannot be resolved > +automatically. In these cases, the livepatch developer must add annotations to > +the livepatch, making it possible for the system to identify which is the > +correct target amongst multiple homonymous symbols. Such annotations must be > +done through a data structure as follows: > + > +struct KLP_MODULE_RELOC(object) data_structure_name[] = { > + KLP_SYMPOS(symbol, pos) > +}; > + > +In the above example, object refers to the object file which contains the > +symbol, being vmlinux or a module; symbol refers to the symbol name that will > +be relocated and pos is its position in the object. > [ ... snip ... ] Should we be explicit about how position is counted? First = 1, second = 2, etc? See the off-by-one bug I pointed out in the "livepatch: Add klp-convert tool" patch earlier. -- Joe