On Mon, 2023-11-06 at 17:25 +0100, Lukas Hruska wrote: > Add a section to Documentation/livepatch/module-elf-format.rst > describing how klp-convert works for fixing relocations. > > Signed-off-by: Lukas Hruska <lhruska@xxxxxxx> Reviewed-by: Marcos Paulo de Souza <mpdesouza@xxxxxxxx> > --- > Documentation/livepatch/module-elf-format.rst | 67 > +++++++++++++++++++ > 1 file changed, 67 insertions(+) > > diff --git a/Documentation/livepatch/module-elf-format.rst > b/Documentation/livepatch/module-elf-format.rst > index a03ed02ec57e..2aa9b11cd806 100644 > --- a/Documentation/livepatch/module-elf-format.rst > +++ b/Documentation/livepatch/module-elf-format.rst > @@ -300,3 +300,70 @@ symbol table, and relocation section indices, > ELF information is preserved for > livepatch modules and is made accessible by the module loader > through > module->klp_info, which is a :c:type:`klp_modinfo` struct. When a > livepatch module > loads, this struct is filled in by the module loader. > + > +6. klp-convert tool > +=================== > +The livepatch relocation sections might be created using > +scripts/livepatch/klp-convert. It is called automatically during > +the build as part of a module post processing. > + > +The tool is not able to find the symbols and all the metadata > +automatically. Instead, all needed information must already be > +part of rela entry for the given symbol. Such a rela can > +be created easily by using KLP_RELOC_SYMBOL() macro after > +the symbol declaration. > + > +KLP_RELOC_SYMBOL causes that the relocation entries for > +the given symbol will be created in the following format:: > + > + .klp.sym.rela.lp_object.sym_object.sym_name,sympos > + ^ ^ ^ ^ ^ ^ ^ ^ ^ > + |___________| |_______| |________| |______| | > + [A] [B] [C] [D] [E] > + > +[A] > + The symbol name is prefixed with the string ".klp.sym.rela." > + > +[B] > + The name of the object (i.e. "vmlinux" or name of module) which > + is livepatched. > + > +[C] > + The name of the object (i.e. "vmlinux" or name of module) to > + which the symbol belongs follows immediately after the prefix. > + > +[D] > + The actual name of the symbol. > + > +[E] > + The position of the symbol in the object (as according to > kallsyms) > + This is used to differentiate duplicate symbols within the same > + object. The symbol position is expressed numerically (0, 1, 2...). > + The symbol position of a unique symbol is 0. > + > +Example: > +-------- > +**Livepatch source code:** > + > +:: > + > + extern char *saved_command_line \ > + KLP_RELOC_SYMBOL(vmlinux, vmlinux, > saved_command_line, 0); > + > +**`readelf -r -W` output of compiled module:** > + > +:: > + > + Relocation section '.rela.text' at offset 0x32e60 contains 10 > entries: > + Offset Info Type > Symbol's Value Symbol's Name + Addend > + ... > + 0000000000000068 0000003c00000002 R_X86_64_PC32 > 0000000000000000 .klp.sym.rela.vmlinux.vmlinux.saved_command_line,0 - > 4 > + ... > + > +**`readelf -r -W` output of transformed module by klp-convert:** > + > +:: > + > + Relocation section '.klp.rela.vmlinux.text' at offset 0x5cb60 > contains 1 entry: > + Offset Info Type > Symbol's Value Symbol's Name + Addend > + 0000000000000068 0000003c00000002 R_X86_64_PC32 > 0000000000000000 .klp.sym.vmlinux.saved_command_line,0 - 4
