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Date: Thu, 31 Aug 2017 11:24:39 -0400
From: Joe Lawrence <joe.lawrence@redhat.com>
To: Joao Moreira <jmoreira@suse.de>
Cc: live-patching@vger.kernel.org, linux-kernel@vger.kernel.org,
        mbenes@suse.cz, mmarek@suse.cz, pmladek@suse.com, jikos@suse.cz,
        nstange@suse.de, jroedel@suse.de, matz@suse.de, jpoimboe@redhat.com,
        khlebnikov@yandex-team.ru, jeyu@kernel.org
Subject: Re: [PATCH 2/8] kbuild: Support for Symbols.list creation
Message-ID: <20170831152439.3qmzrrg4atlj5yve@redhat.com>
References: <20170829190140.401-1-jmoreira@suse.de>
 <20170829190140.401-3-jmoreira@suse.de>
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Hi Joao,

A few nitpicks in-line below...

On Tue, Aug 29, 2017 at 04:01:34PM -0300, Joao Moreira wrote:
> For automatic resolution of livepatch relocations, a file called
> Symbols.list is used. This file maps symbols within every compiled
> kernel object allowing the identification of symbols whose name is
> unique, thus relocation can be automatically inferred, or providing
> information that helps developers when code annotation is required for
> solving the matter.
> 
> Add support for creating Symbols.list in the main Makefile. First,
> ensure that built-in is compiled when CONFIG_LIVEPATCH is enabled (as
> required to achieve a complete Symbols.list file). Define the command to
> build Symbols.list (cmd_klp_map) and hook it in the modules rule.
> 
> As it is undesirable to have symbols from livepatch objects inside
> Symbols.list, make livepatches discernible by modifying
> scripts/Makefile.build to create a .livepatch file for each livepatch
> in $(MODVERDIR). This file is then used by cmd_klp_map to identify and
> bypass livepatches.
> 
> For identifying livepatches during the build process, a flag variable
> LIVEPATCH_$(basetarget).o is considered in scripts/Makefile.build. This
> way, set this flag for the livepatch sample Makefile in
> samples/livepatch/Makefile.

I've never tried building a livepatch out of tree (is that even
possible?) but does this make it any more/less harder?
 
> Finally, Add a clean rule to ensure that Symbols.list is removed during
> clean.
> 
> Notes:
> 
> To achieve a correct Symbols.list file, all kernel objects must be
> considered, thus, its construction require these objects to be priorly
> built. On the other hand, invoking scripts/Makefile.modpost without
> having a complete Symbols.list in place would occasionally lead to
> in-tree livepatches being post-processed incorrectly. To prevent this
> from becoming a circular dependency, the construction of Symbols.list
> uses non-post-processed kernel objects and such does not cause harm as
> the symbols normally referenced from within livepatches are visible at
> this stage. Also due to these requirements, the spot in-between modules
> compilation and the invocation of scripts/Makefile.modpost was picked
> for hooking cmd_klp_map.
> 
> The approach based on .livepatch files was proposed as an alternative
> to using MODULE_INFO statementes. This approach was originally
                       ^^^^^^^^^^^
nit: s/statementes/statements

> proposed by Miroslav Benes as a workaround for identifying livepathces
                                                             ^^^^^^^^^^^
nit: s/livepathces/livepatches

> without depending on modinfo during the modpost stage. It was moved to
> this patch as the approach also shown to be useful while building
> Symbols.list.
> 
> Signed-off-by: Joao Moreira <jmoreira@suse.de>
> ---
>  .gitignore                 |  1 +
>  Makefile                   | 27 ++++++++++++++++++++++++---
>  samples/livepatch/Makefile |  1 +
>  scripts/Makefile.build     |  6 ++++++
>  4 files changed, 32 insertions(+), 3 deletions(-)
> 
> diff --git a/.gitignore b/.gitignore
> index 0c39aa20b6ba..e6a67517a3bc 100644
> --- a/.gitignore
> +++ b/.gitignore
> @@ -39,6 +39,7 @@ Module.symvers
>  *.dwo
>  *.su
>  *.c.[012]*.*
> +Symbols.list
>  
>  #
>  # Top-level generic files
> diff --git a/Makefile b/Makefile
> index e40c471abe29..e1d315e585d8 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -320,10 +320,13 @@ KBUILD_BUILTIN := 1
>  # If we have only "make modules", don't compile built-in objects.
>  # When we're building modules with modversions, we need to consider
>  # the built-in objects during the descend as well, in order to
> -# make sure the checksums are up to date before we record them.
> +# make sure the checksums are up to date before we record them. The
> +# same applies for building livepatches, as built-in objects may hold
> +# symbols which are referenced from livepatches and are required by
> +# klp-convert post-processing tool for resolving these cases.
>  
>  ifeq ($(MAKECMDGOALS),modules)
> -  KBUILD_BUILTIN := $(if $(CONFIG_MODVERSIONS),1)
> +  KBUILD_BUILTIN := $(if $(or $(CONFIG_MODVERSIONS), $(CONFIG_LIVEPATCH)),1)
>  endif
>  
>  # If we have "make <whatever> modules", compile modules
> @@ -1207,9 +1210,24 @@ all: modules
>  # duplicate lines in modules.order files.  Those are removed
>  # using awk while concatenating to the final file.
>  
> +quiet_cmd_klp_map = LIVEPATCH	Symbols.list

nit: I don't think any other quiet_cmd invocations put a tab between the
label and file list.  That said, "LIVEPATCH" is > 8 chars, so it's not
going to line up anyway.

> +SLIST = $(objtree)/Symbols.list
> +
> +define cmd_klp_map
> +	$(shell echo "*vmlinux" > $(SLIST))						\
> +	$(shell nm -f posix $(objtree)/vmlinux | cut -d\  -f1 >> $(SLIST))		\
> +	$(foreach m, $(wildcard $(MODVERDIR)/*.mod),					\
> +		$(eval mod = $(patsubst %.ko,%.o,$(shell head -n1 $(m))))		\
> +		$(if $(wildcard $(MODVERDIR)/$(shell basename -s .o $(mod)).livepatch),,\
> +			$(eval fmod = $(subst $(quote),_,$(subst -,_,$(mod))))		\
> +			$(shell echo "*$(shell basename -s .o $(fmod))" >> $(SLIST))	\
> +			$(shell nm -f posix $(mod) | cut -d\  -f1 >> $(SLIST))))
> +endef
> +
>  PHONY += modules
>  modules: $(vmlinux-dirs) $(if $(KBUILD_BUILTIN),vmlinux) modules.builtin
>  	$(Q)$(AWK) '!x[$$0]++' $(vmlinux-dirs:%=$(objtree)/%/modules.order) > $(objtree)/modules.order
> +	$(if $(CONFIG_LIVEPATCH), $(call cmd,klp_map))
>  	@$(kecho) '  Building modules, stage 2.';
>  	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost
>  	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.fwinst obj=firmware __fw_modbuild
> @@ -1306,7 +1324,10 @@ vmlinuxclean:
>  	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/link-vmlinux.sh clean
>  	$(Q)$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) clean)
>  
> -clean: archclean vmlinuxclean
> +klpclean:
> +	$(Q) rm -f $(objtree)/Symbols.list
> +
> +clean: archclean vmlinuxclean klpclean

Does the klpclean target need to be added to the PHONY variable?

  % touch klpclean
  % make klpclean
  make: 'klpclean' is up to date.
  % ls -l Symbols.list 
  -rw-r--r--. 1 jolawren jolawren 2323179 Aug 29 16:55 Symbols.list

>  
>  # mrproper - Delete all generated files, including .config
>  #
> diff --git a/samples/livepatch/Makefile b/samples/livepatch/Makefile
> index 10319d7ea0b1..955e7ac12d2b 100644
> --- a/samples/livepatch/Makefile
> +++ b/samples/livepatch/Makefile
> @@ -1 +1,2 @@
> +LIVEPATCH_livepatch-sample.o := y
>  obj-$(CONFIG_SAMPLE_LIVEPATCH) += livepatch-sample.o
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 733e044fff8b..d0c32a50cce7 100644<F2>
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -276,6 +276,11 @@ objtool_obj = $(if $(patsubst y%,, \
>  endif # SKIP_STACK_VALIDATION
>  endif # CONFIG_STACK_VALIDATION
>  
> +ifdef CONFIG_LIVEPATCH
> +cmd_livepatch = $(if $(LIVEPATCH_$(basetarget).o),			\
> +	$(shell touch $(MODVERDIR)/$(basetarget).livepatch))
> +endif
> +
>  define rule_cc_o_c
>  	$(call echo-cmd,checksrc) $(cmd_checksrc)			  \
>  	$(call cmd_and_fixdep,cc_o_c)					  \
> @@ -309,6 +314,7 @@ $(single-used-m): $(obj)/%.o: $(src)/%.c $(recordmcount_source) $(objtool_obj) F
>  	$(call if_changed_rule,cc_o_c)
>  	@{ echo $(@:.o=.ko); echo $@; \
>  	   $(cmd_undef_syms); } > $(MODVERDIR)/$(@F:.o=.mod)
> +	$(call cmd_livepatch)
>  
>  quiet_cmd_cc_lst_c = MKLST   $@
>        cmd_cc_lst_c = $(CC) $(c_flags) -g -c -o $*.o $< && \
> -- 
> 2.12.0
> 

I'll try to dig in deeper and tinker with the patchset next week.

Regards,

-- Joe