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    SubjectRe: [PATCH v4 03/10] livepatch: Add klp-convert tool
    On Thu, May 9, 2019 at 11:39 PM Joe Lawrence <joe.lawrence@redhat.com> wrote:
    >
    > From: Josh Poimboeuf <jpoimboe@redhat.com>
    >
    > Livepatches may use symbols which are not contained in its own scope,
    > and, because of that, may end up compiled with relocations that will
    > only be resolved during module load. Yet, when the referenced symbols
    > are not exported, solving this relocation requires information on the
    > object that holds the symbol (either vmlinux or modules) and its
    > position inside the object, as an object may contain multiple symbols
    > with the same name. Providing such information must be done
    > accordingly to what is specified in
    > Documentation/livepatch/module-elf-format.txt.
    >
    > Currently, there is no trivial way to embed the required information
    > as requested in the final livepatch elf object. klp-convert solves
    > this problem in two different forms: (i) by relying on Symbols.list,
    > which is built during kernel compilation, to automatically infer the
    > relocation targeted symbol, and, when such inference is not possible
    > (ii) by using annotations in the elf object to convert the relocation
    > accordingly to the specification, enabling it to be handled by the
    > livepatch loader.
    >
    > Given the above, create scripts/livepatch to hold tools developed for
    > livepatches and add source files for klp-convert there.
    >
    > The core file of klp-convert is scripts/livepatch/klp-convert.c, which
    > implements the heuristics used to solve the relocations and the
    > conversion of unresolved symbols into the expected format, as defined
    > in [1].
    >
    > klp-convert receives as arguments the Symbols.list file, an input
    > livepatch module to be converted and the output name for the converted
    > livepatch. When it starts running, klp-convert parses Symbols.list and
    > builds two internal lists of symbols, one containing the exported and
    > another containing the non-exported symbols. Then, by parsing the rela
    > sections in the elf object, klp-convert identifies which symbols must
    > be converted, which are those unresolved and that do not have a
    > corresponding exported symbol, and attempts to convert them
    > accordingly to the specification.
    >
    > By using Symbols.list, klp-convert identifies which symbols have names
    > that only appear in a single kernel object, thus being capable of
    > resolving these cases without the intervention of the developer. When
    > various homonymous symbols exist through kernel objects, it is not
    > possible to infer the right one, thus klp-convert falls back into
    > using developer annotations. If these were not provided, then the tool
    > will print a list with all acceptable targets for the symbol being
    > processed.
    >
    > Annotations in the context of klp-convert are accessible as struct
    > klp_module_reloc entries in sections named
    > .klp.module_relocs.<objname>. These entries are pairs of symbol
    > references and positions which are to be resolved against definitions
    > in <objname>.
    >
    > Define the structure klp_module_reloc in
    > include/linux/uapi/livepatch.h allowing developers to annotate the
    > livepatch source code with it.
    >
    > klp-convert relies on libelf and on a list implementation. Add files
    > scripts/livepatch/elf.c and scripts/livepatch/elf.h, which are a
    > libelf interfacing layer and scripts/livepatch/list.h, which is a
    > list implementation.
    >
    > Update Makefiles to correctly support the compilation of the new tool,
    > update MAINTAINERS file and add a .gitignore file.
    >
    > [1] - Documentation/livepatch/module-elf-format.txt
    >
    > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
    > Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
    > Signed-off-by: Joao Moreira <jmoreira@suse.de>
    > Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
    > ---
    > MAINTAINERS | 1 +
    > include/uapi/linux/livepatch.h | 5 +
    > scripts/Makefile | 1 +
    > scripts/livepatch/.gitignore | 1 +
    > scripts/livepatch/Makefile | 7 +
    > scripts/livepatch/elf.c | 753 ++++++++++++++++++++++++++++++++
    > scripts/livepatch/elf.h | 73 ++++
    > scripts/livepatch/klp-convert.c | 713 ++++++++++++++++++++++++++++++
    > scripts/livepatch/klp-convert.h | 39 ++
    > scripts/livepatch/list.h | 391 +++++++++++++++++
    > 10 files changed, 1984 insertions(+)
    > create mode 100644 scripts/livepatch/.gitignore
    > create mode 100644 scripts/livepatch/Makefile
    > create mode 100644 scripts/livepatch/elf.c
    > create mode 100644 scripts/livepatch/elf.h
    > create mode 100644 scripts/livepatch/klp-convert.c
    > create mode 100644 scripts/livepatch/klp-convert.h
    > create mode 100644 scripts/livepatch/list.h
    >
    > diff --git a/MAINTAINERS b/MAINTAINERS
    > index 52842fa37261..c1587e1cc385 100644
    > --- a/MAINTAINERS
    > +++ b/MAINTAINERS
    > @@ -9022,6 +9022,7 @@ F: arch/x86/kernel/livepatch.c
    > F: Documentation/livepatch/
    > F: Documentation/ABI/testing/sysfs-kernel-livepatch
    > F: samples/livepatch/
    > +F: scripts/livepatch/
    > F: tools/testing/selftests/livepatch/
    > L: live-patching@vger.kernel.org
    > T: git git://git.kernel.org/pub/scm/linux/kernel/git/livepatching/livepatching.git
    > diff --git a/include/uapi/linux/livepatch.h b/include/uapi/linux/livepatch.h
    > index e19430918a07..1c364d42d38e 100644
    > --- a/include/uapi/linux/livepatch.h
    > +++ b/include/uapi/linux/livepatch.h
    > @@ -12,4 +12,9 @@
    > #define KLP_RELA_PREFIX ".klp.rela."
    > #define KLP_SYM_PREFIX ".klp.sym."
    >
    > +struct klp_module_reloc {
    > + void *sym;
    > + unsigned int sympos;
    > +} __attribute__((packed));
    > +
    > #endif /* _UAPI_LIVEPATCH_H */
    > diff --git a/scripts/Makefile b/scripts/Makefile
    > index 9d442ee050bd..bf9ce74b70b0 100644
    > --- a/scripts/Makefile
    > +++ b/scripts/Makefile
    > @@ -39,6 +39,7 @@ build_unifdef: $(obj)/unifdef
    > subdir-$(CONFIG_GCC_PLUGINS) += gcc-plugins
    > subdir-$(CONFIG_MODVERSIONS) += genksyms
    > subdir-$(CONFIG_SECURITY_SELINUX) += selinux
    > +subdir-$(CONFIG_LIVEPATCH) += livepatch
    >
    > # Let clean descend into subdirs
    > subdir- += basic dtc gdb kconfig mod package
    > diff --git a/scripts/livepatch/.gitignore b/scripts/livepatch/.gitignore
    > new file mode 100644
    > index 000000000000..dc22fe4b6a5b
    > --- /dev/null
    > +++ b/scripts/livepatch/.gitignore
    > @@ -0,0 +1 @@
    > +klp-convert
    > diff --git a/scripts/livepatch/Makefile b/scripts/livepatch/Makefile
    > new file mode 100644
    > index 000000000000..2842ecdba3fd
    > --- /dev/null
    > +++ b/scripts/livepatch/Makefile
    > @@ -0,0 +1,7 @@
    > +hostprogs-y := klp-convert
    > +always := $(hostprogs-y)
    > +
    > +klp-convert-objs := klp-convert.o elf.o
    > +
    > +HOST_EXTRACFLAGS := -g -I$(INSTALL_HDR_PATH)/include -Wall

    This looks strange.

    Theoretically, you cannot include headers in $(INSTALL_HDR_PATH)/include
    from host programs.

    headers_install works for the target architecture, not host architecture.
    This may cause a strange result when you are cross-compiling the kernel.

    BTW, which header in $(INSTALL_HDR_PATH)/include do you need to include ?


    Also, -Wall is redundant because it is set by the top-level Makefile.

    --
    Best Regards
    Masahiro Yamada

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