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>
fixdep is designed only for parsing text files. read_file() appends
a terminating null byte ('\0') and parse_config_file() calls strstr()
to search for CONFIG options.
rustc outputs *.rlib, *.rmeta, *.so to dep-info. fixdep needs them in
the dependency, but there is no point in parsing such binary files.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
Tested-by: Miguel Ojeda <ojeda@kernel.org>
The dep files (*.d files) emitted by C compilers usually contain the
deduplicated list of included files.
One exceptional case is when a header is included by the -include
command line option, and also by #include directive.
For example, the top Makefile adds the command line option,
"-include $(srctree)/include/linux/kconfig.h". You do not need to
include <linux/kconfig.h> in every source file.
In fact, include/linux/kconfig.h is listed twice in many .*.cmd files
due to include/linux/xarray.h having "#include <linux/kconfig.h>".
I did not fix that since it is a small redundancy.
However, this is more annoying for rustc. rustc emits the dependency
for each emission type.
For example, cmd_rustc_library emits dep-info, obj, and metadata.
So, the emitted *.d file contains the dependency for those 3 targets,
which makes fixdep parse the same file 3 times.
$ grep rust/alloc/raw_vec.rs rust/.alloc.o.cmd
rust/alloc/raw_vec.rs \
rust/alloc/raw_vec.rs \
rust/alloc/raw_vec.rs \
To skip the second parsing, this commit adds a hash table for parsed
files, just like we did for CONFIG options.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Tested-by: Miguel Ojeda <ojeda@kernel.org>
Reviewed-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>
Change the hash table code so it will be easier to add the second table.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
Tested-by: Miguel Ojeda <ojeda@kernel.org>
fixdep parses dependency files (*.d) emitted by the compiler.
*.d files are Makefiles describing the dependencies of the main source
file.
fixdep understands minimal Makefile syntax. It works well enough for
GCC and Clang, but not for rustc.
This commit improves the parser a little more for better processing
comments, escape sequences, etc.
My main motivation is to drop comments. rustc may output comments
(e.g. env-dep). Currentyly, rustc build rules invoke sed to remove
comments, but it is more efficient to do it in fixdep.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Tested-by: Miguel Ojeda <ojeda@kernel.org>
The cmd-check macro compares $(cmd_$@) and $(cmd_$1), but a pitfall is
that you cannot use cmd_<target> as the variable name for the command.
For example, the following code will not work in the top Makefile
or ./Kbuild.
quiet_cmd_foo = GEN $@
cmd_foo = touch $@
targets += foo
foo: FORCE
$(call if_changed,foo)
In this case, both $@ and $1 are expanded to 'foo', so $(cmd_check)
is always empty.
We do not need to use the same prefix for cmd_$@ and cmd_$1.
Rename the former to savedcmd_$@.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
This is unneeded since commit 69304379ff ("fixdep: use fflush() and
ferror() to ensure successful write to files").
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Currently, fixdep checks the return value from (v)printf(), but it does
not ensure the complete write to the .cmd file.
printf() just writes data to the internal buffer, which usually succeeds.
(Of course, it may fail for another reason, for example when the file
descriptor is closed, but that is another story.)
When the buffer (4k?) is full, an actual write occurs, and printf() may
really fail. One of typical cases is "No space left on device" when the
disk is full.
The data remaining in the buffer will be pushed out to the file when
the program exits, but we never know if it is successful.
One straight-forward fix would be to add the following code at the end
of the program.
ret = fflush(stdout);
if (ret < 0) {
/* error handling */
}
However, it is tedious to check the return code in all the call sites
of printf(), fflush(), fclose(), and whatever can cause actual writes
to the end device. Doing that lets the program bail out at the first
failure but is usually not worth the effort.
Instead, let's check the error status from ferror(). This is 'sticky',
so you need to check it just once. You still need to call fflush().
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: David Laight <david.laight@aculab.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
To build host programs, you need to add the program names to 'hostprogs'
to use the necessary build rule, but it is not enough to build them
because there is no dependency.
There are two types of host programs: built as the prerequisite of
another (e.g. gen_crc32table in lib/Makefile), or always built when
Kbuild visits the Makefile (e.g. genksyms in scripts/genksyms/Makefile).
The latter is typical in Makefiles under scripts/, which contains host
programs globally used during the kernel build. To build them, you need
to add them to both 'hostprogs' and 'always-y'.
This commit adds hostprogs-always-y as a shorthand.
The same applies to user programs. net/bpfilter/Makefile builds
bpfilter_umh on demand, hence always-y is unneeded. In contrast,
programs under samples/ are added to both 'userprogs' and 'always-y'
so they are always built when Kbuild visits the Makefiles.
userprogs-always-y works as a shorthand.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:
struct foo {
int stuff;
struct boo array[];
};
By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.
Also, notice that, dynamic memory allocations won't be affected by
this change:
"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]
sizeof(flexible-array-member) triggers a warning because flexible array
members have incomplete type[1]. There are some instances of code in
which the sizeof operator is being incorrectly/erroneously applied to
zero-length arrays and the result is zero. Such instances may be hiding
some bugs. So, this work (flexible-array member conversions) will also
help to get completely rid of those sorts of issues.
This issue was found with the help of Coccinelle.
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 7649773293 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Pull SPDX updates from Greg KH:
"Here are three SPDX patches for 5.7-rc1.
One fixes up the SPDX tag for a single driver, while the other two go
through the tree and add SPDX tags for all of the .gitignore files as
needed.
Nothing too complex, but you will get a merge conflict with your
current tree, that should be trivial to handle (one file modified by
two things, one file deleted.)
All three of these have been in linux-next for a while, with no
reported issues other than the merge conflict"
* tag 'spdx-5.7-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/spdx:
ASoC: MT6660: make spdxcheck.py happy
.gitignore: add SPDX License Identifier
.gitignore: remove too obvious comments
If *q is '\0', the condition (isalnum(*q) || *q == '_') is false anyway.
It is redundant to ensure non-zero *q.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
This is probably stale code. In old days (~ Linux 2.5.59), Kbuild made
genksyms generate include/linux/modules/*.ver files.
The currenct Kbuild does not generate *.ver files at all.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
In old days, the "host-progs" syntax was used for specifying host
programs. It was renamed to the current "hostprogs-y" in 2004.
It is typically useful in scripts/Makefile because it allows Kbuild to
selectively compile host programs based on the kernel configuration.
This commit renames like follows:
always -> always-y
hostprogs-y -> hostprogs
So, scripts/Makefile will look like this:
always-$(CONFIG_BUILD_BIN2C) += ...
always-$(CONFIG_KALLSYMS) += ...
...
hostprogs := $(always-y) $(always-m)
I think this makes more sense because a host program is always a host
program, irrespective of the kernel configuration. We want to specify
which ones to compile by CONFIG options, so always-y will be handier.
The "always", "hostprogs-y", "hostprogs-m" will be kept for backward
compatibility for a while.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Kbuild descends into scripts/basic/ even before the Kconfig.
I do not expect any other host programs added to this Makefile.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
When there is not enough space on your storage device, the build will
fail with 'No space left on device' error message.
The reason is obvious from the message, so you will free up some disk
space, then you will resume the build.
However, sometimes you may still see a mysterious error message:
unterminated call to function 'wildcard': missing ')'.
If you run out of the disk space, fixdep may end up with generating
incomplete .*.cmd files.
For example, if the disk-full error occurs while fixdep is running
print_dep(), the .*.cmd might be truncated like this:
$(wildcard include/config/
When you run 'make' next time, this broken .*.cmd will be included,
then Make will terminate parsing since it is a wrong syntax.
Once this happens, you need to run 'make clean' or delete the broken
.*.cmd file manually.
Even if you do not see any error message, the .*.cmd files after any
error could be potentially incomplete, and unreliable. You may miss
the re-compilation due to missing header dependency.
If printf() cannot output the string for disk shortage or whatever
reason, it returns a negative value, but currently fixdep does not
check it at all. Consequently, fixdep *successfully* generates a
broken .*.cmd file. Make never notices that since fixdep exits with 0,
which means success.
Given the intended usage of fixdep, it must respect the return value
of not only malloc(), but also printf() and putchar().
This seems a long-standing issue since the introduction of fixdep.
In old days, Kbuild tried to provide an extra safety by letting fixdep
output to a temporary file and renaming it after everything is done:
scripts/basic/fixdep $(depfile) $@ '$(make-cmd)' > $(dot-target).tmp;\
rm -f $(depfile); \
mv -f $(dot-target).tmp $(dot-target).cmd)
It was no help to avoid the current issue; fixdep successfully created
a truncated tmp file, which would be renamed to a .*.cmd file.
This problem should be fixed by propagating the error status to the
build system because:
[1] Since commit 9c2af1c737 ("kbuild: add .DELETE_ON_ERROR special
target"), Make will delete the target automatically on any failure
in the recipe.
[2] Since commit 392885ee82 ("kbuild: let fixdep directly write to
.*.cmd files"), .*.cmd file is included only when the corresponding
target already exists.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Add SPDX license identifiers to all Make/Kconfig files which:
- Have no license information of any form
These files fall under the project license, GPL v2 only. The resulting SPDX
license identifier is:
GPL-2.0-only
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
My main motivation of this commit is to clean up scripts/Kbuild.include
and scripts/Makefile.build.
Currently, CONFIG_TRIM_UNUSED_KSYMS works with a tricky gimmick;
possibly exported symbols are detected by letting $(CPP) replace
EXPORT_SYMBOL* with a special string '=== __KSYM_*===', which is
post-processed by sed, and passed to fixdep. The extra preprocessing
is costly, and hacking cmd_and_fixdep is ugly.
I came up with a new way to find exported symbols; insert a dummy
symbol __ksym_marker_* to each potentially exported symbol. Those
dummy symbols are picked up by $(NM), post-processed by sed, then
appended to .*.cmd files. I collected the post-process part to a
new shell script scripts/gen_ksymdeps.sh for readability. The dummy
symbols are put into the .discard.* section so that the linker
script rips them off the final vmlinux or modules.
A nice side-effect is building with CONFIG_TRIM_UNUSED_KSYMS will
be much faster.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Nicolas Pitre <nico@linaro.org>
Commit 8370edea81 ("bin2c: move bin2c in scripts/basic") moved bin2c
to the scripts/basic/ directory, incorrectly stating "Kexec wants to
use bin2c and it wants to use it really early in the build process.
See arch/x86/purgatory/ code in later patches."
Commit bdab125c93 ("Revert "kexec/purgatory: Add clean-up for
purgatory directory"") and commit d6605b6bbe ("x86/build: Remove
unnecessary preparation for purgatory") removed the redundant
purgatory build magic entirely.
That means that the move of bin2c was unnecessary in the first place.
fixdep is the only host program that deserves to sit in the
scripts/basic/ directory.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Underscores in symbol names are translated into slashes for path names.
Filesystems treat consecutive slashes as if there was only one, so
let's do the same in the dependency list for easier grepping, etc.
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
The idea of using fixdep was inspired by Kconfig, but autoksyms
belongs to a different group. So, I want to move those touched
files under include/config/ksym/ to include/ksym/.
The directory include/ksym/ can be removed by 'make clean' because
it is meaningless for the external module building.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
