If you know that your kernel modules will only ever be loaded by a newer
kernel, you can disable BASIC_MODVERSIONS to save space. This also
allows easy creation of test modules to see how tooling will respond to
modules that only have the new format.
Signed-off-by: Matthew Maurer <mmaurer@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Generate both the existing modversions format and the new extended one
when running modpost. Presence of this metadata in the final .ko is
guarded by CONFIG_EXTENDED_MODVERSIONS.
We no longer generate an error on long symbols in modpost if
CONFIG_EXTENDED_MODVERSIONS is set, as they can now be appropriately
encoded in the extended section. These symbols will be skipped in the
previous encoding. An error will still be generated if
CONFIG_EXTENDED_MODVERSIONS is not set.
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Matthew Maurer <mmaurer@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
With the previous changes, $(extmod_prefix), $(MODORDER), and
$(MODULES_NSDEPS) are constant. (empty, modules.order, and
modules.nsdeps, respectively).
Remove these variables and hard-code their values.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Currently, Kbuild always operates in the output directory of the kernel,
even when building external modules. This increases the risk of external
module Makefiles attempting to write to the kernel directory.
This commit switches the working directory to the external module
directory, allowing the removal of the $(KBUILD_EXTMOD)/ prefix from
some build artifacts.
The command for building external modules maintains backward
compatibility, but Makefiles that rely on working in the kernel
directory may break. In such cases, $(objtree) and $(srctree) should
be used to refer to the output and source directories of the kernel.
The appearance of the build log will change as follows:
[Before]
$ make -C /path/to/my/linux M=/path/to/my/externel/module
make: Entering directory '/path/to/my/linux'
CC [M] /path/to/my/externel/module/helloworld.o
MODPOST /path/to/my/externel/module/Module.symvers
CC [M] /path/to/my/externel/module/helloworld.mod.o
CC [M] /path/to/my/externel/module/.module-common.o
LD [M] /path/to/my/externel/module/helloworld.ko
make: Leaving directory '/path/to/my/linux'
[After]
$ make -C /path/to/my/linux M=/path/to/my/externel/module
make: Entering directory '/path/to/my/linux'
make[1]: Entering directory '/path/to/my/externel/module'
CC [M] helloworld.o
MODPOST Module.symvers
CC [M] helloworld.mod.o
CC [M] .module-common.o
LD [M] helloworld.ko
make[1]: Leaving directory '/path/to/my/externel/module'
make: Leaving directory '/path/to/my/linux'
Printing "Entering directory" twice is cumbersome. This will be
addressed later.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <n.schier@avm.de>
$(objtree) refers to the top of the output directory of kernel builds.
This commit adds the explicit $(objtree)/ prefix to build artifacts
needed for building external modules.
This change has no immediate impact, as the top-level Makefile
currently defines:
objtree := .
This commit prepares for supporting the building of external modules
in a different directory.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Pull Kbuild updates from Masahiro Yamada:
- Avoid 'constexpr', which is a keyword in C23
- Allow 'dtbs_check' and 'dt_compatible_check' run independently of
'dt_binding_check'
- Fix weak references to avoid GOT entries in position-independent code
generation
- Convert the last use of 'optional' property in arch/sh/Kconfig
- Remove support for the 'optional' property in Kconfig
- Remove support for Clang's ThinLTO caching, which does not work with
the .incbin directive
- Change the semantics of $(src) so it always points to the source
directory, which fixes Makefile inconsistencies between upstream and
downstream
- Fix 'make tar-pkg' for RISC-V to produce a consistent package
- Provide reasonable default coverage for objtool, sanitizers, and
profilers
- Remove redundant OBJECT_FILES_NON_STANDARD, KASAN_SANITIZE, etc.
- Remove the last use of tristate choice in drivers/rapidio/Kconfig
- Various cleanups and fixes in Kconfig
* tag 'kbuild-v6.10' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (46 commits)
kconfig: use sym_get_choice_menu() in sym_check_prop()
rapidio: remove choice for enumeration
kconfig: lxdialog: remove initialization with A_NORMAL
kconfig: m/nconf: merge two item_add_str() calls
kconfig: m/nconf: remove dead code to display value of bool choice
kconfig: m/nconf: remove dead code to display children of choice members
kconfig: gconf: show checkbox for choice correctly
kbuild: use GCOV_PROFILE and KCSAN_SANITIZE in scripts/Makefile.modfinal
Makefile: remove redundant tool coverage variables
kbuild: provide reasonable defaults for tool coverage
modules: Drop the .export_symbol section from the final modules
kconfig: use menu_list_for_each_sym() in sym_check_choice_deps()
kconfig: use sym_get_choice_menu() in conf_write_defconfig()
kconfig: add sym_get_choice_menu() helper
kconfig: turn defaults and additional prompt for choice members into error
kconfig: turn missing prompt for choice members into error
kconfig: turn conf_choice() into void function
kconfig: use linked list in sym_set_changed()
kconfig: gconf: use MENU_CHANGED instead of SYMBOL_CHANGED
kconfig: gconf: remove debug code
...
If UNUSED_KSYMS_WHITELIST is a file generated
before Kbuild runs, and the source tree is in
a read-only filesystem, the developer must put
the file somewhere and specify an absolute
path to UNUSED_KSYMS_WHITELIST. This worked,
but if IKCONFIG=y, an absolute path is embedded
into .config and eventually into vmlinux, causing
the build to be less reproducible when building
on a different machine.
This patch makes the handling of
UNUSED_KSYMS_WHITELIST to be similar to
MODULE_SIG_KEY.
First, check if UNUSED_KSYMS_WHITELIST is an
absolute path, just as before this patch. If so,
use the path as is.
If it is a relative path, use wildcard to check
the existence of the file below objtree first.
If it does not exist, fall back to the original
behavior of adding $(srctree)/ before the value.
After this patch, the developer can put the generated
file in objtree, then use a relative path against
objtree in .config, eradicating any absolute paths
that may be evaluated differently on different machines.
Signed-off-by: Yifan Hong <elsk@google.com>
Reviewed-by: Elliot Berman <quic_eberman@quicinc.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Kbuild conventionally uses $(obj)/ for generated files, and $(src)/ for
checked-in source files. It is merely a convention without any functional
difference. In fact, $(obj) and $(src) are exactly the same, as defined
in scripts/Makefile.build:
src := $(obj)
When the kernel is built in a separate output directory, $(src) does
not accurately reflect the source directory location. While Kbuild
resolves this discrepancy by specifying VPATH=$(srctree) to search for
source files, it does not cover all cases. For example, when adding a
header search path for local headers, -I$(srctree)/$(src) is typically
passed to the compiler.
This introduces inconsistency between upstream and downstream Makefiles
because $(src) is used instead of $(srctree)/$(src) for the latter.
To address this inconsistency, this commit changes the semantics of
$(src) so that it always points to the directory in the source tree.
Going forward, the variables used in Makefiles will have the following
meanings:
$(obj) - directory in the object tree
$(src) - directory in the source tree (changed by this commit)
$(objtree) - the top of the kernel object tree
$(srctree) - the top of the kernel source tree
Consequently, $(srctree)/$(src) in upstream Makefiles need to be replaced
with $(src).
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Currently, all files with EXPORT_SYMBOL() are rebuilt when CONFIG_MODULES
is flipped due to <linux/export.h> depending on CONFIG_MODULES.
Now that modpost can make a final decision about export symbols,
<linux/export.h> does not need to make EXPORT_SYMBOL() no-op.
Instead, modpost can skip emitting KSYMTAB when CONFIG_MODULES is unset.
This commit will reduce the number of recompilation when CONFIG_MODULES
is toggled.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
When CONFIG_TRIM_UNUSED_KSYMS is enabled, Kbuild recursively traverses
the directory tree to determine which EXPORT_SYMBOL to trim. If an
EXPORT_SYMBOL turns out to be unused by anyone, Kbuild begins the
second traverse, where some source files are recompiled with their
EXPORT_SYMBOL() tuned into a no-op.
Linus stated negative opinions about this slowness in commits:
- 5cf0fd591f ("Kbuild: disable TRIM_UNUSED_KSYMS option")
- a555bdd0c5 ("Kbuild: enable TRIM_UNUSED_KSYMS again, with some guarding")
We can do this better now. The final data structures of EXPORT_SYMBOL
are generated by the modpost stage, so modpost can selectively emit
KSYMTAB entries that are really used by modules.
Commit f73edc8951 ("kbuild: unify two modpost invocations") is another
ground-work to do this in a one-pass algorithm. With the list of modules,
modpost sets sym->used if it is used by a module. modpost emits KSYMTAB
only for symbols with sym->used==true.
BTW, Nicolas explained why the trimming was implemented with recursion:
https://lore.kernel.org/all/2o2rpn97-79nq-p7s2-nq5-8p83391473r@syhkavp.arg/
Actually, we never achieved that level of optimization where the chain
reaction of trimming comes into play because:
- CONFIG_LTO_CLANG cannot remove any unused symbols
- CONFIG_LD_DEAD_CODE_DATA_ELIMINATION is enabled only for vmlinux,
but not modules
If deeper trimming is required, we need to revisit this, but I guess
that is unlikely to happen.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
"No build warning" is a strong requirement these days, so you must fix
all issues before enabling a new warning flag.
We often add a new warning to W=1 first so that the kbuild test robot
blocks new breakages.
This commit allows modpost to show extra warnings only when W=1
(or KBUILD_EXTRA_WARN=1) is given.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
When there is a missing input file (vmlinux.o or Module.symvers), you
are likely to get a ton of unresolved symbols.
Currently, Kbuild automatically adds the -w option to allow module builds
to continue with warnings instead of errors.
This may not be what the user expects because it is generally more useful
to catch all possible issues at build time instead of at run time.
Let's not do what the user did not ask.
If you still want to build modules anyway, you can proceed by explicitly
setting KBUILD_MODPOST_WARN=1. Since you may miss a real issue, you need
to be aware of what you are doing.
Suggested-by: William McVicker <willmcvicker@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Will McVicker <willmcvicker@google.com>
Commit 63ffe00d8c ("kbuild: Fix running modpost with musl libc")
accidentally turned the unresolved symbol warnings into errors when
vmlinux.o (for in-tree builds) or Module.symver (for external module
builds) is missing.
In those cases, unresolved symbols are expected, but the -w option
is not set because 'missing-input' is referenced before set.
Move $(missing-input) back to the original place. This should be fine
for musl libc because vmlinux.o and -w are not added at the same time.
With this change, -w may be passed twice, but it is not a big deal.
Link: https://lore.kernel.org/all/b56a03b8-2a2a-f833-a5d2-cdc50a7ca2bb@cschramm.eu/
Fixes: 63ffe00d8c ("kbuild: Fix running modpost with musl libc")
Reported-by: Christopher Schramm <debian@cschramm.eu>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Samuel Holland <samuel@sholland.org>
commit 3d57e1b7b1 ("kbuild: refactor the prerequisites of the modpost
rule") moved 'vmlinux.o' inside modpost-args, possibly before some of
the other options. However, getopt() in musl libc follows POSIX and
stops looking for options upon reaching the first non-option argument.
As a result, the '-T' option is misinterpreted as a positional argument,
and the build fails:
make -f ./scripts/Makefile.modpost
scripts/mod/modpost -E -o Module.symvers vmlinux.o -T modules.order
-T: No such file or directory
make[1]: *** [scripts/Makefile.modpost:137: Module.symvers] Error 1
make: *** [Makefile:1960: modpost] Error 2
The fix is to move all options before 'vmlinux.o' in modpost-args.
Fixes: 3d57e1b7b1 ("kbuild: refactor the prerequisites of the modpost rule")
Signed-off-by: Samuel Holland <samuel@sholland.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
The prerequisites of modpost are cluttered. The variables *-if-present
and *-if-needed are unreadable.
It is cleaner to append them into modpost-deps.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
scripts/Makefile.build replaces the suffix .o with .ko, then
scripts/Makefile.modpost calls the sed command to change .ko back
to the original .o suffix.
Instead of converting the suffixes back-and-forth, store the .o paths
in modules.order, and replace it with .ko in 'make modules_install'.
This avoids the unneeded sed command.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
While building, installing, cleaning, Kbuild visits sub-directories
and includes 'Kbuild' or 'Makefile' that exists there.
Add 'kbuild-file' macro, and reuse it from scripts/Makefie.*
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Reviewed-by: Alexander Lobakin <alobakin@pm.me>
Tested-by: Alexander Lobakin <alobakin@pm.me>
Commit f73edc8951 ("kbuild: unify two modpost invocations") introduced
a typo (moudle.symvers-if-present) which results in the kernel's
Module.symvers to not be included as a prerequisite for
$(KBUILD_EXTMOD)/Module.symvers. Fix the typo to restore the intended
functionality.
Fixes: f73edc8951 ("kbuild: unify two modpost invocations")
Signed-off-by: Will McVicker <willmcvicker@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
The objects placed at the head of vmlinux need special treatments:
- arch/$(SRCARCH)/Makefile adds them to head-y in order to place
them before other archives in the linker command line.
- arch/$(SRCARCH)/kernel/Makefile adds them to extra-y instead of
obj-y to avoid them going into built-in.a.
This commit gets rid of the latter.
Create vmlinux.a to collect all the objects that are unconditionally
linked to vmlinux. The objects listed in head-y are moved to the head
of vmlinux.a by using 'ar m'.
With this, arch/$(SRCARCH)/kernel/Makefile can consistently use obj-y
for builtin objects.
There is no *.o that is directly linked to vmlinux. Drop unneeded code
in scripts/clang-tools/gen_compile_commands.py.
$(AR) mPi needs 'T' to workaround the llvm-ar bug. The fix was suggested
by Nathan Chancellor [1].
[1]: https://lore.kernel.org/llvm/YyjjT5gQ2hGMH0ni@dev-arch.thelio-3990X/
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Modpost generates .vmlinux.export.c and *.mod.c, which are prerequisites
of vmlinux and modules, respectively.
The modpost stage should be re-run when the modpost code is updated.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Currently, modpost is executed twice; first for vmlinux, second
for modules.
This commit merges them.
Current build flow
==================
1) build obj-y and obj-m objects
2) link vmlinux.o
3) modpost for vmlinux
4) link vmlinux
5) modpost for modules
6) link modules (*.ko)
The build steps 1) through 6) are serialized, that is, modules are
built after vmlinux. You do not get benefits of parallel builds when
scripts/link-vmlinux.sh is being run.
New build flow
==============
1) build obj-y and obj-m objects
2) link vmlinux.o
3) modpost for vmlinux and modules
4a) link vmlinux
4b) link modules (*.ko)
In the new build flow, modpost is invoked just once.
vmlinux and modules are built in parallel. One exception is
CONFIG_DEBUG_INFO_BTF_MODULES=y, where modules depend on vmlinux.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
.vmlinux.objs is used by modpost, so scripts/Makefile.modpost is
a better place to generate it.
It is used only when CONFIG_MODVERSIONS=y. It should be guarded
by "ifdef CONFIG_MODVERSIONS".
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
When CONFIG_LTO_CLANG=y, additional intermediate *.prelink.o is created
for each module. Also, objtool is postponed until LLVM IR is converted
to ELF.
CONFIG_X86_KERNEL_IBT works in a similar way to postpone objtool until
objects are merged together.
This commit stops generating *.prelink.o, so the build flow will look
similar with/without LTO.
The following figures show how the LTO build currently works, and
how this commit is changing it.
Current build flow
==================
[1] single-object module
$(LD)
$(CC) +objtool $(LD)
foo.c --------------------> foo.o -----> foo.prelink.o -----> foo.ko
(LLVM IR) (ELF) | (ELF)
|
foo.mod.o --/
(LLVM IR)
[2] multi-object module
$(LD)
$(CC) $(AR) +objtool $(LD)
foo1.c -----> foo1.o -----> foo.o -----> foo.prelink.o -----> foo.ko
| (archive) (ELF) | (ELF)
foo2.c -----> foo2.o --/ |
(LLVM IR) foo.mod.o --/
(LLVM IR)
One confusion is that foo.o in multi-object module is an archive
despite of its suffix.
New build flow
==============
[1] single-object module
Since there is only one object, there is no need to keep the LLVM IR.
Use $(CC)+$(LD) to generate an ELF object in one build rule. When LTO
is disabled, $(LD) is unneeded because $(CC) produces an ELF object.
$(CC)+$(LD)+objtool $(LD)
foo.c ----------------------------> foo.o ---------> foo.ko
(ELF) | (ELF)
|
foo.mod.o --/
(LLVM IR)
[2] multi-object module
Previously, $(AR) was used to combine LLVM IR files into an archive,
but there was no technical reason to do so. Use $(LD) to merge them
into a single ELF object.
$(LD)
$(CC) +objtool $(LD)
foo1.c ---------> foo1.o ---------> foo.o ---------> foo.ko
| (ELF) | (ELF)
foo2.c ---------> foo2.o ----/ |
(LLVM IR) foo.mod.o --/
(LLVM IR)
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # LLVM-14 (x86-64)
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
