kbuild: generate offset range data for builtin modules

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@oracle.com>
Reviewed-by: Nick Alcock <nick.alcock@oracle.com>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Tested-by: Sam James <sam@gentoo.org>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Tested-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Author: kvanhees

.gitignore

@@ -69,6 +69,7 @@ modules.order
 /Module.markers
 /modules.builtin
 /modules.builtin.modinfo
+/modules.builtin.ranges
 /modules.nsdeps
 
 #

Documentation/dontdiff

@@ -180,6 +180,7 @@ modpost
 modules-only.symvers
 modules.builtin
 modules.builtin.modinfo
+modules.builtin.ranges
 modules.nsdeps
 modules.order
 modversions.h*

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
 =====================

Documentation/process/changes.rst

@@ -64,6 +64,7 @@ GNU tar                1.28             tar --version
 gtags (optional)       6.6.5            gtags --version
 mkimage (optional)     2017.01          mkimage --version
 Python (optional)      3.5.x            python3 --version
+GNU AWK (optional)     5.1.0            gawk --version
 ====================== ===============  ========================================
 
 .. [#f1] Sphinx is needed only to build the Kernel documentation
@@ -192,6 +193,12 @@ platforms. The tool is available via the ``u-boot-tools`` package or can be
 built from the U-Boot source code. See the instructions at
 https://docs.u-boot.org/en/latest/build/tools.html#building-tools-for-linux
 
+GNU AWK
+-------
+
+GNU AWK is needed if you want kernel builds to generate address range data for
+builtin modules (CONFIG_BUILTIN_MODULE_RANGES).
+
 System utilities
 ****************
 

Makefile

@@ -1482,6 +1482,7 @@ endif # CONFIG_MODULES
 # Directories & files removed with 'make clean'
 CLEAN_FILES += vmlinux.symvers modules-only.symvers \
 	       modules.builtin modules.builtin.modinfo modules.nsdeps \
+	       modules.builtin.ranges vmlinux.o.map \
 	       compile_commands.json rust/test \
 	       rust-project.json .vmlinux.objs .vmlinux.export.c
 

lib/Kconfig.debug

@@ -571,6 +571,21 @@ config VMLINUX_MAP
 	  pieces of code get eliminated with
 	  CONFIG_LD_DEAD_CODE_DATA_ELIMINATION.
 
+config BUILTIN_MODULE_RANGES
+	bool "Generate address range information for builtin modules"
+	depends on !LTO
+	depends on VMLINUX_MAP
+	help
+	 When modules are built into the kernel, there will be no module name
+	 associated with its symbols in /proc/kallsyms.  Tracers may want to
+	 identify symbols by module name and symbol name regardless of whether
+	 the module is configured as loadable or not.
+
+	 This option generates modules.builtin.ranges in the build tree with
+	 offset ranges (per ELF section) for the module(s) they belong to.
+	 It also records an anchor symbol to determine the load address of the
+	 section.
+
 config DEBUG_FORCE_WEAK_PER_CPU
 	bool "Force weak per-cpu definitions"
 	depends on DEBUG_KERNEL

scripts/Makefile.vmlinux

@@ -33,6 +33,24 @@ targets += vmlinux
 vmlinux: scripts/link-vmlinux.sh vmlinux.o $(KBUILD_LDS) FORCE
 	+$(call if_changed_dep,link_vmlinux)
 
+# module.builtin.ranges
+# ---------------------------------------------------------------------------
+ifdef CONFIG_BUILTIN_MODULE_RANGES
+__default: modules.builtin.ranges
+
+quiet_cmd_modules_builtin_ranges = GEN     $@
+      cmd_modules_builtin_ranges = gawk -f $(real-prereqs) > $@
+
+targets += modules.builtin.ranges
+modules.builtin.ranges: $(srctree)/scripts/generate_builtin_ranges.awk \
+			modules.builtin vmlinux.map vmlinux.o.map FORCE
+	$(call if_changed,modules_builtin_ranges)
+
+vmlinux.map: vmlinux
+	@:
+
+endif
+
 # Add FORCE to the prerequisites of a target to force it to be always rebuilt.
 # ---------------------------------------------------------------------------
 

scripts/Makefile.vmlinux_o

@@ -45,9 +45,12 @@ objtool-args = $(vmlinux-objtool-args-y) --link
 # Link of vmlinux.o used for section mismatch analysis
 # ---------------------------------------------------------------------------
 
+vmlinux-o-ld-args-$(CONFIG_BUILTIN_MODULE_RANGES)	+= -Map=$@.map
+
 quiet_cmd_ld_vmlinux.o = LD      $@
       cmd_ld_vmlinux.o = \
 	$(LD) ${KBUILD_LDFLAGS} -r -o $@ \
+	$(vmlinux-o-ld-args-y) \
 	$(addprefix -T , $(initcalls-lds)) \
 	--whole-archive vmlinux.a --no-whole-archive \
 	--start-group $(KBUILD_VMLINUX_LIBS) --end-group \