Message-ID: <CAK7LNAS53tB708sRSbCA=_2GP_sAoNYHtLzhYMV=5U-+FfcR3Q@mail.gmail.com>
Date: Thu, 19 Sep 2024 23:28:44 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Kris Van Hees <kris.van.hees@...cle.com>
Cc: linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org, 
	linux-modules@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	Nick Alcock <nick.alcock@...cle.com>, Alan Maguire <alan.maguire@...cle.com>, 
	Steven Rostedt <rostedt@...dmis.org>, Sam James <sam@...too.org>, 
	Luis Chamberlain <mcgrof@...nel.org>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Jiri Olsa <olsajiri@...il.com>, 
	Elena Zannoni <elena.zannoni@...cle.com>
Subject: Re: [PATCH v10 2/4] kbuild: generate offset range data for builtin modules

Hi Kris,



On Tue, Sep 10, 2024 at 4:43 AM Kris Van Hees <kris.van.hees@...cle.com> wrote:
>
> On Sun, Sep 08, 2024 at 11:50:51AM +0900, Masahiro Yamada wrote:
> > On Fri, Sep 6, 2024 at 11:45???PM Kris Van Hees <kris.van.hees@...cle.com> wrote:
> > >
> > > Create file module.builtin.ranges that can be used to find where
> > > built-in modules are located by their addresses. This will be useful for
> > > tracing tools to find what functions are for various built-in modules.
> > >
> > > The offset range data for builtin modules is generated using:
> > >  - modules.builtin: associates object files with module names
> > >  - vmlinux.map: provides load order of sections and offset of first member
> > >     per section
> > >  - vmlinux.o.map: provides offset of object file content per section
> > >  - .*.cmd: build cmd file with KBUILD_MODFILE
> > >
> > > The generated data will look like:
> > >
> > > .text 00000000-00000000 = _text
> > > .text 0000baf0-0000cb10 amd_uncore
> > > .text 0009bd10-0009c8e0 iosf_mbi
> > > ...
> > > .text 00b9f080-00ba011a intel_skl_int3472_discrete
> > > .text 00ba0120-00ba03c0 intel_skl_int3472_discrete intel_skl_int3472_tps68470
> > > .text 00ba03c0-00ba08d6 intel_skl_int3472_tps68470
> > > ...
> > > .data 00000000-00000000 = _sdata
> > > .data 0000f020-0000f680 amd_uncore
> > >
> > > For each ELF section, it lists the offset of the first symbol.  This can
> > > be used to determine the base address of the section at runtime.
> > >
> > > Next, it lists (in strict ascending order) offset ranges in that section
> > > that cover the symbols of one or more builtin modules.  Multiple ranges
> > > can apply to a single module, and ranges can be shared between modules.
> > >
> > > The CONFIG_BUILTIN_MODULE_RANGES option controls whether offset range data
> > > is generated for kernel modules that are built into the kernel image.
> > >
> > > How it works:
> > >
> > >  1. The modules.builtin file is parsed to obtain a list of built-in
> > >     module names and their associated object names (the .ko file that
> > >     the module would be in if it were a loadable module, hereafter
> > >     referred to as <kmodfile>).  This object name can be used to
> > >     identify objects in the kernel compile because any C or assembler
> > >     code that ends up into a built-in module will have the option
> > >     -DKBUILD_MODFILE=<kmodfile> present in its build command, and those
> > >     can be found in the .<obj>.cmd file in the kernel build tree.
> > >
> > >     If an object is part of multiple modules, they will all be listed
> > >     in the KBUILD_MODFILE option argument.
> > >
> > >     This allows us to conclusively determine whether an object in the
> > >     kernel build belong to any modules, and which.
> > >
> > >  2. The vmlinux.map is parsed next to determine the base address of each
> > >     top level section so that all addresses into the section can be
> > >     turned into offsets.  This makes it possible to handle sections
> > >     getting loaded at different addresses at system boot.
> > >
> > >     We also determine an 'anchor' symbol at the beginning of each
> > >     section to make it possible to calculate the true base address of
> > >     a section at runtime (i.e. symbol address - symbol offset).
> > >
> > >     We collect start addresses of sections that are included in the top
> > >     level section.  This is used when vmlinux is linked using vmlinux.o,
> > >     because in that case, we need to look at the vmlinux.o linker map to
> > >     know what object a symbol is found in.
> > >
> > >     And finally, we process each symbol that is listed in vmlinux.map
> > >     (or vmlinux.o.map) based on the following structure:
> > >
> > >     vmlinux linked from vmlinux.a:
> > >
> > >       vmlinux.map:
> > >         <top level section>
> > >           <included section>  -- might be same as top level section)
> > >             <object>          -- built-in association known
> > >               <symbol>        -- belongs to module(s) object belongs to
> > >               ...
> > >
> > >     vmlinux linked from vmlinux.o:
> > >
> > >       vmlinux.map:
> > >         <top level section>
> > >           <included section>  -- might be same as top level section)
> > >             vmlinux.o         -- need to use vmlinux.o.map
> > >               <symbol>        -- ignored
> > >               ...
> > >
> > >       vmlinux.o.map:
> > >         <section>
> > >             <object>          -- built-in association known
> > >               <symbol>        -- belongs to module(s) object belongs to
> > >               ...
> > >
> > >  3. As sections, objects, and symbols are processed, offset ranges are
> > >     constructed in a straight-forward way:
> > >
> > >       - If the symbol belongs to one or more built-in modules:
> > >           - If we were working on the same module(s), extend the range
> > >             to include this object
> > >           - If we were working on another module(s), close that range,
> > >             and start the new one
> > >       - If the symbol does not belong to any built-in modules:
> > >           - If we were working on a module(s) range, close that range
> > >
> > > Signed-off-by: Kris Van Hees <kris.van.hees@...cle.com>
> > > Reviewed-by: Nick Alcock <nick.alcock@...cle.com>
> > > Reviewed-by: Alan Maguire <alan.maguire@...cle.com>
> > > Reviewed-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> > > Tested-by: Sam James <sam@...too.org>
> > > ---
> >
> >
> > If v10 is the final version, I offer to locally squash the following:
>
> Thanks!  That would be great!  v10 is indeed the final version (see bwlow).
>
> > diff --git a/.gitignore b/.gitignore
> > index c06a3ef6d6c6..625bf59ad845 100644
> > --- a/.gitignore
> > +++ b/.gitignore
> > @@ -69,6 +69,7 @@ modules.order
> >  /Module.markers
> >  /modules.builtin
> >  /modules.builtin.modinfo
> > +/modules.builtin.ranges
> >  /modules.nsdeps
> >
> >  #
> > diff --git a/Documentation/dontdiff b/Documentation/dontdiff
> > index 3c399f132e2d..a867aea95c40 100644
> > --- a/Documentation/dontdiff
> > +++ b/Documentation/dontdiff
> > @@ -180,6 +180,7 @@ modpost
> >  modules-only.symvers
> >  modules.builtin
> >  modules.builtin.modinfo
> > +modules.builtin.ranges
> >  modules.nsdeps
> >  modules.order
> >  modversions.h*
>
> > If Sami reports more errors and you end up with v11,
> > please remember to fold it.
>
> Sami confirmed v10 [0].  Can you squash his reviewed-by and tested-by as well?
>
> Thanks for all the help!
>
>         Kris
>
> [0] https://lore.kernel.org/lkml/20240909191801.GA398180@google.com/





Can you please add a small explanation to
Documentation/kbuild/kbuild.rst ?


It documents modules.order, modules.builtin, modules.builtin.modinfo.

Having modules.builtin.ranges there will keep the consistency.



You do not need to re-submit the entire patch.

If you provide a diff in a few days,
I will locally squash it.







--
Best Regards
Masahiro Yamada

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