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Building external modules is typically done using this command:
$ make -C <KERNEL_DIR> M=<EXTMOD_DIR>
Here, <KERNEL_DIR> refers to the output directory where the kernel was
built, not the kernel source directory.
When the kernel is built in the source tree, there is no ambiguity, as
the output directory and the source directory are the same.
If the kernel was built in a separate build directory, <KERNEL_DIR>
should be the kernel output directory. Otherwise, Kbuild cannot locate
necessary build artifacts. This has been the method for building
external modules against a pre-built kernel in a separate directory
for over 20 years. [1]
If you pass the kernel source directory to the -C option, you must also
specify the kernel build directory using the O= option. This approach
works as well, though it results in a slightly longer command:
$ make -C <KERNEL_SOURCE_DIR> O=<KERNEL_BUILD_DIR> M=<EXTMOD_DIR>
Some people mistakenly believe that O= should specify a build directory
for external modules when used together with M=. This commit adds more
clarification to Documentation/kbuild/kbuild.rst.
[1]: https://git.kernel.org/pub/scm/linux/kernel/git/history/history.git/commit/?id=e321b2ec2eb2993b3d0116e5163c78ad923e3c54
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <n.schier@avm.de>
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The use of shipped files is discouraged in the upstream kernel these
days. [1]
Downstream Makefiles have the freedom to use shipped files or other
options to handle binaries, but this should not be advertised in the
upstream document.
[1]: https://lore.kernel.org/all/CAHk-=wgSEi_ZrHdqr=20xv+d6dr5G895CbOAi8ok+7-CQUN=fQ@mail.gmail.com/
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <n.schier@avm.de>
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Do similar to commit 1a4c1c9df72e ("docs/kbuild/makefiles: drop section
numbering, use references").
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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Do similar to commit 5e8f0ba38a4d ("docs/kbuild/makefiles: throw out the
local table of contents").
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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Kbuild used to manipulate header search paths, enforcing the odd
limitation of "no space after -I".
Commit cdd750bfb1f7 ("kbuild: remove 'addtree' and 'flags' magic for
header search paths") stopped doing that. This limitation no longer
exists. Instead, you need to accurately specify the header search path.
(In this case, $(src)/include)
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <n.schier@avm.de>
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This description was added 20 years ago [1]. It does not convey any
useful information except for a feeling of nostalgia.
[1]: https://git.kernel.org/pub/scm/linux/kernel/git/history/history.git/commit/?id=65e433436b5794ae056d22ddba60fe9194bba007
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <n.schier@avm.de>
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The phrase "In newer versions of the kernel" was added 14 years ago, by
commit efdf02cf0651 ("Documentation/kbuild: major edit of modules.txt
sections 1-4"). This feature is no longer new, so remove it and update
the paragraph.
Example 3 was written 20 years ago [1]. There is no need to note about
backward compatibility with such an old build system. Remove Example 3
entirely.
[1]: https://git.kernel.org/pub/scm/linux/kernel/git/history/history.git/commit/?id=65e433436b5794ae056d22ddba60fe9194bba007
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <n.schier@avm.de>
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If RUST_LIB_SRC is defined in the top-level Makefile (via an environment
variable or command line), it is already exported.
The only situation where it is defined but not exported is when the
top-level Makefile is wrapped by another Makefile (e.g., GNUmakefile).
I cannot think of any other use cases.
I know some people use this tip to define custom variables. However,
even in that case, you can export it directly in the wrapper Makefile.
Example GNUmakefile:
export RUST_LIB_SRC = /path/to/your/sysroot/lib/rustlib/src/rust/library
include Makefile
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
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The append operation was introduced in
commit b1a1a1a09b46 ("kbuild: lto: postpone objtool")
when the command was created from two parts.
In commit 850ded46c642 ("kbuild: Fix TRIM_UNUSED_KSYMS with LTO_CLANG")
however the first part was removed again, making the append operation
unnecessary.
To keep this command definition aligned with all other command
definitions, remove the append again.
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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Cache expression values to avoid recalculating them repeatedly.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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Currently, every expression in Kconfig files produces a new abstract
syntax tree (AST), even if it is identical to a previously encountered
one.
Consider the following code:
config FOO
bool "FOO"
depends on (A || B) && C
config BAR
bool "BAR"
depends on (A || B) && C
config BAZ
bool "BAZ"
depends on A || B
The "depends on" lines are similar, but currently a separate AST is
allocated for each one.
The current data structure looks like this:
FOO->dep ==> AND BAR->dep ==> AND BAZ->dep ==> OR
/ \ / \ / \
OR C OR C A B
/ \ / \
A B A B
This is redundant; FOO->dep and BAR->dep have identical ASTs but
different memory instances.
We can optimize this; FOO->dep and BAR->dep can share the same AST, and
BAZ->dep can reference its sub tree.
The optimized data structure looks like this:
FOO->dep, BAR->dep ==> AND
/ \
BAZ->dep ==> OR C
/ \
A B
This commit introduces a hash table to keep track of allocated
expressions. If an identical expression is found, it is reused.
This does not necessarily result in memory savings, as menu_finalize()
transforms expressions without freeing up stale ones. This will be
addressed later.
One optimization that can be easily implemented is caching the
expression's value. Once FOO's dependency, (A || B) && C, is calculated,
it can be cached, eliminating the need to recalculate it for BAR.
This commit also reverts commit e983b7b17ad1 ("kconfig/menu.c: fix
multiple references to expressions in menu_add_prop()").
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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Currently, expr_eliminate_dups() passes two identical pointers down to
expr_eliminate_dups1(), which later skips processing identical leaves.
This approach is somewhat tricky and, more importantly, it will not work
with the refactoring made in the next commit.
This commit slightly changes the recursion logic; it deduplicates both
the left and right arms, and then passes them to expr_eliminate_dups1().
expr_eliminate_dups() should produce the same result.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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Provide explanations for complex transformations.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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This clarifies the behavior of these functions.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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This function was originally added by commit 8af27e1dc4e4 ("fixdep: use
hash table instead of a single array").
Move it to scripts/include/ so that other host programs can use it.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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Change the 'overflow' variable to bool. Also, remove unnecessary
parentheses.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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After commit 64e166099b69 ("kallsyms: get rid of code for absolute,
kallsyms"), there is only one call site for output_address(). Squash it.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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When CONFIG_BUILTIN_MODULE_RANGES is enabled, the modules.builtin.ranges
file should be installed in the module install location.
Signed-off-by: Kris Van Hees <kris.van.hees@oracle.com>
Reviewed-by: Nick Alcock <nick.alcock@oracle.com>
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>
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Masahiro Yamada
Thomas Weißschuh
Kris Van Hees