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Message-ID: <ZuyRPYFl4uDijwNg@kvh-deb-bpf.us.oracle.com>
Date: Thu, 19 Sep 2024 17:01:49 -0400
From: Kris Van Hees <kris.van.hees@...cle.com>
To: Masahiro Yamada <masahiroy@...nel.org>
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
On Thu, Sep 19, 2024 at 11:28:44PM +0900, Masahiro Yamada wrote:
> 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.
Thank you for offering to locally squash the diff.
Kris
diff --git a/Documentation/kbuild/kbuild.rst b/Documentation/kbuild/kbuild.rst
index 9c8d1d046ea5..142be0c74761 100644
--- a/Documentation/kbuild/kbuild.rst
+++ b/Documentation/kbuild/kbuild.rst
@@ -22,6 +22,11 @@ modules.builtin.modinfo
This file contains modinfo from all modules that are built into the kernel.
Unlike modinfo of a separate module, all fields are prefixed with module name.
+modules.builtin.ranges
+----------------------
+This file contains address offset ranges (per ELF section) for all modules
+that are built into the kernel. Together with System.map, it can be used
+to associate module names with symbols.
Environment variables
=====================
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