modpost: Allow extended modversions without basic MODVERSIONS

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 a

modpost: Allow extended modversions without basic MODVERSIONS

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 <[email protected]>
Signed-off-by: Masahiro Yamada <[email protected]>

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modpost: Produce extended MODVERSIONS information

Generate both the existing modversions format and the new extended one
when running modpost. Presence of this metadata in the final .ko is
guarded b

modpost: Produce extended MODVERSIONS information

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 <[email protected]>
Signed-off-by: Matthew Maurer <[email protected]>
Signed-off-by: Masahiro Yamada <[email protected]>

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kbuild: remove extmod_prefix, MODORDER, MODULES_NSDEPS variables

With the previous changes, $(extmod_prefix), $(MODORDER), and
$(MODULES_NSDEPS) are constant. (empty, modules.order, and
modules.nsde

kbuild: remove extmod_prefix, MODORDER, MODULES_NSDEPS variables

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 <[email protected]>
Reviewed-by: Nicolas Schier <[email protected]>

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kbuild: change working directory to external module directory with M=

Currently, Kbuild always operates in the output directory of the kernel,
even when building external modules. This increases the

kbuild: change working directory to external module directory with M=

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 <[email protected]>
Reviewed-by: Nicolas Schier <[email protected]>

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kbuild: add $(objtree)/ prefix to some in-kernel build artifacts

$(objtree) refers to the top of the output directory of kernel builds.

This commit adds the explicit $(objtree)/ prefix to build art

kbuild: add $(objtree)/ prefix to some in-kernel build artifacts

$(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 <[email protected]>
Reviewed-by: Nicolas Schier <[email protected]>

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module: allow UNUSED_KSYMS_WHITELIST to be relative against objtree.

If UNUSED_KSYMS_WHITELIST is a file generated
before Kbuild runs, and the source tree is in
a read-only filesystem, the developer

module: allow UNUSED_KSYMS_WHITELIST to be relative against objtree.

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 <[email protected]>
Reviewed-by: Elliot Berman <[email protected]>
Signed-off-by: Luis Chamberlain <[email protected]>

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kbuild: use $(src) instead of $(srctree)/$(src) for source directory

Kbuild conventionally uses $(obj)/ for generated files, and $(src)/ for
checked-in source files. It is merely a convention withou

kbuild: use $(src) instead of $(srctree)/$(src) for source directory

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 <[email protected]>
Reviewed-by: Nicolas Schier <[email protected]>

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linux/export.h: make <linux/export.h> independent of CONFIG_MODULES

Currently, all files with EXPORT_SYMBOL() are rebuilt when CONFIG_MODULES
is flipped due to <linux/export.h> depending on CONFIG_M

linux/export.h: make <linux/export.h> independent of CONFIG_MODULES

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 <[email protected]>

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kbuild: implement CONFIG_TRIM_UNUSED_KSYMS without recursion

When CONFIG_TRIM_UNUSED_KSYMS is enabled, Kbuild recursively traverses
the directory tree to determine which EXPORT_SYMBOL to trim. If an

kbuild: implement CONFIG_TRIM_UNUSED_KSYMS without recursion

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:

- 5cf0fd591f2e ("Kbuild: disable TRIM_UNUSED_KSYMS option")
- a555bdd0c58c ("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 f73edc8951b2 ("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/[email protected]/

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 <[email protected]>

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modpost: propagate W=1 build option to modpost

"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=

modpost: propagate W=1 build option to modpost

"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 <[email protected]>
Reviewed-by: Nick Desaulniers <[email protected]>

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kbuild: do not automatically add -w option to modpost

When there is a missing input file (vmlinux.o or Module.symvers), you
are likely to get a ton of unresolved symbols.

Currently, Kbuild automati

kbuild: do not automatically add -w option to modpost

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 <[email protected]>
Signed-off-by: Masahiro Yamada <[email protected]>
Tested-by: Will McVicker <[email protected]>

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kbuild: readd -w option when vmlinux.o or Module.symver is missing

Commit 63ffe00d8c93 ("kbuild: Fix running modpost with musl libc")
accidentally turned the unresolved symbol warnings into errors w

kbuild: readd -w option when vmlinux.o or Module.symver is missing

Commit 63ffe00d8c93 ("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/[email protected]/
Fixes: 63ffe00d8c93 ("kbuild: Fix running modpost with musl libc")
Reported-by: Christopher Schramm <[email protected]>
Signed-off-by: Masahiro Yamada <[email protected]>
Tested-by: Samuel Holland <[email protected]>

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kbuild: Fix running modpost with musl libc

commit 3d57e1b7b1d4 ("kbuild: refactor the prerequisites of the modpost
rule") moved 'vmlinux.o' inside modpost-args, possibly before some of
the other opt

kbuild: Fix running modpost with musl libc

commit 3d57e1b7b1d4 ("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: 3d57e1b7b1d4 ("kbuild: refactor the prerequisites of the modpost rule")
Signed-off-by: Samuel Holland <[email protected]>
Reviewed-by: Nathan Chancellor <[email protected]>
Signed-off-by: Masahiro Yamada <[email protected]>

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kbuild: refactor the prerequisites of the modpost rule

The prerequisites of modpost are cluttered. The variables *-if-present
and *-if-needed are unreadable.

It is cleaner to append them into modpo

kbuild: refactor the prerequisites of the modpost rule

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 <[email protected]>

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kbuild: change module.order to list *.o instead of *.ko

scripts/Makefile.build replaces the suffix .o with .ko, then
scripts/Makefile.modpost calls the sed command to change .ko back
to the original

kbuild: change module.order to list *.o instead of *.ko

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 <[email protected]>
Reviewed-by: Luis Chamberlain <[email protected]>

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kbuild: add kbuild-file macro

While building, installing, cleaning, Kbuild visits sub-directories
and includes 'Kbuild' or 'Makefile' that exists there.

Add 'kbuild-file' macro, and reuse it from s

kbuild: add kbuild-file macro

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 <[email protected]>
Reviewed-by: Nicolas Schier <[email protected]>
Reviewed-by: Alexander Lobakin <[email protected]>
Tested-by: Alexander Lobakin <[email protected]>

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kbuild: fix typo in modpost

Commit f73edc8951b2 ("kbuild: unify two modpost invocations") introduced
a typo (moudle.symvers-if-present) which results in the kernel's
Module.symvers to not be include

kbuild: fix typo in modpost

Commit f73edc8951b2 ("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: f73edc8951b2 ("kbuild: unify two modpost invocations")
Signed-off-by: Will McVicker <[email protected]>
Signed-off-by: Masahiro Yamada <[email protected]>

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modpost: put modpost options before argument

The musl implementation of getopt stops looking for options after the
first non-option argument. Put the options before the non-option
argument so enviro

modpost: put modpost options before argument

The musl implementation of getopt stops looking for options after the
first non-option argument. Put the options before the non-option
argument so environments using musl can still build the kernel and
modules.

Fixes: f73edc8951b2 ("kbuild: unify two modpost invocations")
Link: https://git.musl-libc.org/cgit/musl/tree/src/misc/getopt.c?h=dc9285ad1dc19349c407072cc48ba70dab86de45#n44
Signed-off-by: Richard Acayan <[email protected]>
Signed-off-by: Masahiro Yamada <[email protected]>

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kbuild: use obj-y instead extra-y for objects placed at the head

The objects placed at the head of vmlinux need special treatments:

- arch/$(SRCARCH)/Makefile adds them to head-y in order to place

kbuild: use obj-y instead extra-y for objects placed at the head

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/[email protected]/

Signed-off-by: Masahiro Yamada <[email protected]>
Tested-by: Nick Desaulniers <[email protected]>
Reviewed-by: Nicolas Schier <[email protected]>

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kbuild: re-run modpost when it is updated

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

kbuild: re-run modpost when it is updated

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 <[email protected]>

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kbuild: unify two modpost invocations

Currently, modpost is executed twice; first for vmlinux, second
for modules.

This commit merges them.

Current build flow
==================

1) build obj-y

kbuild: unify two modpost invocations

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 <[email protected]>
Tested-by: Nick Desaulniers <[email protected]>
Reviewed-by: Nicolas Schier <[email protected]>

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kbuild: move .vmlinux.objs rule to Makefile.modpost

.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 sho

kbuild: move .vmlinux.objs rule to Makefile.modpost

.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 <[email protected]>
Tested-by: Nick Desaulniers <[email protected]>
Reviewed-by: Nicolas Schier <[email protected]>

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kbuild: do not create *.prelink.o for Clang LTO or IBT

When CONFIG_LTO_CLANG=y, additional intermediate *.prelink.o is created
for each module. Also, objtool is postponed until LLVM IR is converted

kbuild: do not create *.prelink.o for Clang LTO or IBT

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 <[email protected]>
Reviewed-by: Nicolas Schier <[email protected]>
Tested-by: Nathan Chancellor <[email protected]>
Reviewed-by: Sami Tolvanen <[email protected]>
Tested-by: Sedat Dilek <[email protected]> # LLVM-14 (x86-64)
Acked-by: Josh Poimboeuf <[email protected]>

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kbuild: replace $(if A,A,B) with $(or A,B) in scripts/Makefile.modpost

Similar cleanup to commit 5c8166419acf ("kbuild: replace $(if A,A,B)
with $(or A,B)").

Signed-off-by: Masahiro Yamada <masahir

kbuild: replace $(if A,A,B) with $(or A,B) in scripts/Makefile.modpost

Similar cleanup to commit 5c8166419acf ("kbuild: replace $(if A,A,B)
with $(or A,B)").

Signed-off-by: Masahiro Yamada <[email protected]>
Reviewed-by: Nick Desaulniers <[email protected]>

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kbuild: Fix include path in scripts/Makefile.modpost

When building an external module, if users don't need to separate the
compilation output and source code, they run the following command:
"make -

kbuild: Fix include path in scripts/Makefile.modpost

When building an external module, if users don't need to separate the
compilation output and source code, they run the following command:
"make -C $(LINUX_SRC_DIR) M=$(PWD)". At this point, "$(KBUILD_EXTMOD)"
and "$(src)" are the same.

If they need to separate them, they run "make -C $(KERNEL_SRC_DIR)
O=$(KERNEL_OUT_DIR) M=$(OUT_DIR) src=$(PWD)". Before running the
command, they need to copy "Kbuild" or "Makefile" to "$(OUT_DIR)" to
prevent compilation failure.

So the kernel should change the included path to avoid the copy operation.

Signed-off-by: Jing Leng <[email protected]>
[masahiro: I do not think "M=$(OUT_DIR) src=$(PWD)" is the official way,
but this patch is a nice clean up anyway.]
Signed-off-by: Masahiro Yamada <[email protected]>

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