In Kbuild, some files are generated by chains of pattern/implicit rules.
For example, *.dtb.o files in drivers/of/unittest-data/Makefile are
generated by the chain of 3 pattern rules, like this:
%.dts -> %.dtb -> %.dtb.S -> %.dtb.o
Here, %.dts is the real source, %.dtb.o is the final target.
%.dtb and %.dtb.S are called "intermediate files".
As GNU Make manual [1] says, intermediate files are treated differently
in two ways:
(a) The first difference is what happens if the intermediate file does
not exist. If an ordinary file 'b' does not exist, and make considers
a target that depends on 'b', it invariably creates 'b' and then
updates the target from 'b'. But if 'b' is an intermediate file, then
make can leave well enough alone: it won't create 'b' unless one of
its prerequisites is out of date. This means the target depending
on 'b' won't be rebuilt either, unless there is some other reason
to update that target: for example the target doesn't exist or a
different prerequisite is newer than the target.
(b) The second difference is that if make does create 'b' in order to
update something else, it deletes 'b' later on after it is no longer
needed. Therefore, an intermediate file which did not exist before
make also does not exist after make. make reports the deletion to
you by printing a 'rm' command showing which file it is deleting.
The combination of these is problematic for Kbuild because most of the
build rules depend on FORCE and the if_changed* macros really determine
if the target should be updated. So, all missing files, whether they
are intermediate or not, are always rebuilt.
To see the problem, delete ".SECONDARY:" from scripts/Kbuild.include,
and repeat this command:
$ make allmodconfig drivers/of/unittest-data/
The intermediate files will be deleted, which results in rebuilding
intermediate and final objects in the next run of make.
In the old days, people suppressed (b) in inconsistent ways.
As commit 54a702f705 ("kbuild: mark $(targets) as .SECONDARY and
remove .PRECIOUS markers") noted, you should not use .PRECIOUS because
.PRECIOUS has the following behavior (c), which is not likely what you
want.
(c) If make is killed or interrupted during the execution of their
recipes, the target is not deleted. Also, the target is not deleted
on error even if .DELETE_ON_ERROR is specified.
.SECONDARY is a much better way to disable (b), but a small problem
is that .SECONDARY enables (a), which gives a side-effect to $?;
prerequisites marked as .SECONDARY do not appear in $?. This is a
drawback for Kbuild.
I thought it was a bug and opened a bug report. As Paul, the GNU Make
maintainer, concluded in [2], this is not a bug.
A good news is that, GNU Make 4.4 added the perfect solution,
.NOTINTERMEDIATE, which cancels both (a) and (b).
For clarificaton, my understanding of .INTERMEDIATE, .SECONDARY,
.PRECIOUS and .NOTINTERMEDIATE are as follows:
(a) (b) (c)
.INTERMEDIATE enable enable disable
.SECONDARY enable disable disable
.PRECIOUS disable disable enable
.NOTINTERMEDIATE disable disable disable
However, GNU Make 4.4 has a bug for the global .NOTINTERMEDIATE. [3]
It was fixed by commit 6164608900ad ("[SV 63417] Ensure global
.NOTINTERMEDIATE disables all intermediates"), and will be available
in the next release of GNU Make.
The following is the gain for .NOTINTERMEDIATE:
[Current Make]
$ make allnoconfig vmlinux
[ full build ]
$ rm include/linux/device.h
$ make vmlinux
CALL scripts/checksyscalls.sh
Make does not notice the removal of <linux/device.h>.
[Future Make]
$ make-latest allnoconfig vmlinux
[ full build ]
$ rm include/linux/device.h
$ make-latest vmlinux
CC arch/x86/kernel/asm-offsets.s
In file included from ./include/linux/writeback.h:13,
from ./include/linux/memcontrol.h:22,
from ./include/linux/swap.h:9,
from ./include/linux/suspend.h:5,
from arch/x86/kernel/asm-offsets.c:13:
./include/linux/blk_types.h:11:10: fatal error: linux/device.h: No such file or directory
11 | #include <linux/device.h>
| ^~~~~~~~~~~~~~~~
compilation terminated.
make-latest[1]: *** [scripts/Makefile.build:114: arch/x86/kernel/asm-offsets.s] Error 1
make-latest: *** [Makefile:1282: prepare0] Error 2
Make notices the removal of <linux/device.h>, and rebuilds objects
that depended on <linux/device.h>. There exists a source file that
includes <linux/device.h>, and it raises an error.
To see detailed background information, refer to commit 2d3b1b8f0d
("kbuild: drop $(wildcard $^) check in if_changed* for faster rebuild").
[1]: https://www.gnu.org/software/make/manual/make.html#Chained-Rules
[2]: https://savannah.gnu.org/bugs/?55532
[3]: https://savannah.gnu.org/bugs/?63417
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Since GNU Make 4.2, $(file ...) supports the read operater '<', which
is useful to read a file without forking a new process. No warning is
shown even if the input file is missing.
For older Make versions, it falls back to the cat command.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Reviewed-by: Alexander Lobakin <alexandr.lobakin@intel.com>
Tested-by: Alexander Lobakin <alexandr.lobakin@intel.com>
GNU Make 4.4 introduced $(intcmp ...), which is useful to compare two
integers without forking a new process.
Add test-{ge,gt,le,lt} macros, which work more efficiently with GNU
Make >= 4.4. For older Make versions, they fall back to the 'test'
shell command.
The first two parameters to $(intcmp ...) must not be empty. To avoid
the syntax error, I appended '0' to them. Fortunately, '00' is treated
as '0'. This is needed because CONFIG options may expand to an empty
string when the kernel configuration is not included.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com> # RISC-V
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
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>
When receiving some signal, GNU Make automatically deletes the target if
it has already been changed by the interrupted recipe.
If the target is possibly incomplete due to interruption, it must be
deleted so that it will be remade from scratch on the next run of make.
Otherwise, the target would remain corrupted permanently because its
timestamp had already been updated.
Thanks to this behavior of Make, you can stop the build any time by
pressing Ctrl-C, and just run 'make' to resume it.
Kbuild also relies on this feature, but it is equivalently important
for any build systems that make decisions based on timestamps (if you
want to support Ctrl-C reliably).
However, this does not always work as claimed; Make immediately dies
with Ctrl-C if its stderr goes into a pipe.
[Test Makefile]
foo:
echo hello > $@
sleep 3
echo world >> $@
[Test Result]
$ make # hit Ctrl-C
echo hello > foo
sleep 3
^Cmake: *** Deleting file 'foo'
make: *** [Makefile:3: foo] Interrupt
$ make 2>&1 | cat # hit Ctrl-C
echo hello > foo
sleep 3
^C$ # 'foo' is often left-over
The reason is because SIGINT is sent to the entire process group.
In this example, SIGINT kills 'cat', and 'make' writes the message to
the closed pipe, then dies with SIGPIPE before cleaning the target.
A typical bad scenario (as reported by [1], [2]) is to save build log
by using the 'tee' command:
$ make 2>&1 | tee log
This can be problematic for any build systems based on Make, so I hope
it will be fixed in GNU Make. The maintainer of GNU Make stated this is
a long-standing issue and difficult to fix [3]. It has not been fixed
yet as of writing.
So, we cannot rely on Make cleaning the target. We can do it by
ourselves, in signal traps.
As far as I understand, Make takes care of SIGHUP, SIGINT, SIGQUIT, and
SITERM for the target removal. I added the traps for them, and also for
SIGPIPE just in case cmd_* rule prints something to stdout or stderr
(but I did not observe an actual case where SIGPIPE was triggered).
[Note 1]
The trap handler might be worth explaining.
rm -f $@; trap - $(sig); kill -s $(sig) $$
This lets the shell kill itself by the signal it caught, so the parent
process can tell the child has exited on the signal. Generally, this is
a proper manner for handling signals, in case the calling program (like
Bash) may monitor WIFSIGNALED() and WTERMSIG() for WCE although this may
not be a big deal here because GNU Make handles SIGHUP, SIGINT, SIGQUIT
in WUE and SIGTERM in IUE.
IUE - Immediate Unconditional Exit
WUE - Wait and Unconditional Exit
WCE - Wait and Cooperative Exit
For details, see "Proper handling of SIGINT/SIGQUIT" [4].
[Note 2]
Reverting 392885ee82 ("kbuild: let fixdep directly write to .*.cmd
files") would directly address [1], but it only saves if_changed_dep.
As reported in [2], all commands that use redirection can potentially
leave an empty (i.e. broken) target.
[Note 3]
Another (even safer) approach might be to always write to a temporary
file, and rename it to $@ at the end of the recipe.
<command> > $(tmp-target)
mv $(tmp-target) $@
It would require a lot of Makefile changes, and result in ugly code,
so I did not take it.
[Note 4]
A little more thoughts about a pattern rule with multiple targets (or
a grouped target).
%.x %.y: %.z
<recipe>
When interrupted, GNU Make deletes both %.x and %.y, while this solution
only deletes $@. Probably, this is not a big deal. The next run of make
will execute the rule again to create $@ along with the other files.
[1]: https://lore.kernel.org/all/YLeot94yAaM4xbMY@gmail.com/
[2]: https://lore.kernel.org/all/20220510221333.2770571-1-robh@kernel.org/
[3]: https://lists.gnu.org/archive/html/help-make/2021-06/msg00001.html
[4]: https://www.cons.org/cracauer/sigint.html
Fixes: 392885ee82 ("kbuild: let fixdep directly write to .*.cmd files")
Reported-by: Ingo Molnar <mingo@kernel.org>
Reported-by: Rob Herring <robh@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Separate out the command execution part of if_changed, as we did
for if_changed_dep.
This allows us to reuse it in if_changed_rule.
define rule_foo
$(call cmd_and_savecmd,foo)
$(call cmd,bar)
endef
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nicolas Schier <n.schier@avm.de>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # LLVM-14 (x86-64)
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>
The complex macro, config_filename, was introduced to do:
[1] drop double-quotes from the string value
[2] add $(srctree)/ prefix in case the file is not found in $(objtree)
[3] escape spaces and more
[1] will be more generally handled by Kconfig later.
As for [2], Kbuild uses VPATH to search for files in $(objtree),
$(srctree) in this order. GNU Make can natively handle it.
As for [3], converting $(space) to $(space_escape) back and forth looks
questionable to me. It is well-known that GNU Make cannot handle file
paths with spaces in the first place.
Instead of using the complex macro, use $< so it will be expanded to
the file path of the key.
Remove config_filename, finally.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
if_changed, if_changed_dep, and if_changed_rule must have FORCE as a
prerequisite so the command line change is detected.
Documentation/kbuild/makefiles.rst clearly explains it:
Note: It is a typical mistake to forget the FORCE prerequisite.
However, not all people follow the document.
This mistake occurred again and again, so a compelling force is needed.
Show a warning if FORCE is missing in the prerequisite of if_changed
and friends. Same for filechk.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Nicolas Schier <n.schier@avm.de>
Add a new macro that expands into $(newer-prereqs)$(cmd-check).
It makes it easier to add common code for if_changed, if_changed_dep,
and if_changed_rule.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
When building with 'make -s', no output to stdout should be printed.
As Arnd Bergmann reported [1], mkimage shows the detailed information
of the generated images.
I think this should be suppressed by the 'cmd' macro instead of by
individual scripts.
Insert 'exec >/dev/null;' in order to redirect stdout to /dev/null for
silent builds.
[Note about this implementation]
'exec >/dev/null;' may look somewhat tricky, but this has a reason.
Appending '>/dev/null' at the end of command line is a common way for
redirection, so I first tried this:
cmd = @set -e; $(echo-cmd) $(cmd_$(1)) >/dev/null
... but it would not work if $(cmd_$(1)) itself contains a redirection.
For example, cmd_wrap in scripts/Makefile.asm-generic redirects the
output from the 'echo' command into the target file.
It would be expanded into:
echo "#include <asm-generic/$*.h>" > $@ >/dev/null
Then, the target file gets empty because the string will go to /dev/null
instead of $@.
Next, I tried this:
cmd = @set -e; $(echo-cmd) { $(cmd_$(1)); } >/dev/null
The form above would be expanded into:
{ echo "#include <asm-generic/$*.h>" > $@; } >/dev/null
This works as expected. However, it would be a syntax error if
$(cmd_$(1)) is empty.
When CONFIG_TRIM_UNUSED_KSYMS is disabled, $(call cmd,gen_ksymdeps) in
scripts/Makefile.build would be expanded into:
set -e; { ; } >/dev/null
..., which causes an syntax error.
I also tried this:
cmd = @set -e; $(echo-cmd) ( $(cmd_$(1)) ) >/dev/null
... but this causes a syntax error for the same reason.
So, finally I adopted:
cmd = @set -e; $(echo-cmd) exec >/dev/null; $(cmd_$(1))
[1]: https://lore.kernel.org/lkml/20210514135752.2910387-1-arnd@kernel.org/
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
scripts/Kbuild.include is included everywhere, but macros such as
cc-option are needed by build targets only.
For example, when 'make clean' traverses the tree, it does not need
to evaluate $(call cc-option,).
Split cc-option, ld-option, etc. to scripts/Makefile.compiler, which
is only included from the top Makefile and scripts/Makefile.build.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
There is no direct user of ld-version; you can use CONFIG_LD_VERSION
if needed.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
After commit 43fee2b238 ("kbuild: do not redirect the first
prerequisite for filechk"), the rule is no longer automatically passed
$< as stdin, so remove the stale comment.
Fixes: 43fee2b238 ("kbuild: do not redirect the first prerequisite for filechk")
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Commit d26e941492 ("kbuild: no gcc-plugins during cc-option tests")
was neeeded because scripts/Makefile.gcc-plugins was too early.
This is unneeded by including scripts/Makefile.gcc-plugins last,
and being careful to not add cc-option tests after it.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
When cc-option and friends evaluate compiler flags, the temporary file
$$TMP is created as an output object, and automatically cleaned up.
The actual file path of $$TMP is .<pid>.tmp, here <pid> is the process
ID of $(shell ...) invoked from cc-option. (Please note $$$$ is the
escape sequence of $$).
Such garbage files are cleaned up in most cases, but some compiler flags
create additional output files.
For example, -gsplit-dwarf creates a .dwo file.
When CONFIG_DEBUG_INFO_SPLIT=y, you will see a bunch of .<pid>.dwo files
left in the top of build directories. You may not notice them unless you
do 'ls -a', but the garbage files will increase every time you run 'make'.
This commit changes the temporary object path to .tmp_<pid>/tmp, and
removes .tmp_<pid> directory when exiting. Separate build artifacts such
as *.dwo will be cleaned up all together because their file paths are
usually determined based on the base name of the object.
Another example is -ftest-coverage, which outputs the coverage data into
<base-name-of-object>.gcno
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
This omits system headers from the generated header dependency.
System headers are not updated unless you upgrade the compiler. Nor do
they contain CONFIG options, so fixdep does not need to parse them.
Having said that, the effect of this optimization will be quite small
because the kernel code generally does not include system headers
except <stdarg.h>. Host programs include a lot of system headers,
but there are not so many in the kernel tree.
At first, keeping system headers in .*.cmd files might be useful to
detect the compiler update, but there is no guarantee that <stdarg.h>
is included from every file. So, I implemented a more reliable way in
the previous commit.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Bartosz Golaszewski reports that when "make {menu,n,g,x}config" fails
due to missing packages, a temporary file is left over, which is not
ignored by git.
For example, if GTK+ is not installed:
$ make gconfig
*
* Unable to find the GTK+ installation. Please make sure that
* the GTK+ 2.0 development package is correctly installed.
* You need gtk+-2.0 gmodule-2.0 libglade-2.0
*
scripts/kconfig/Makefile:208: recipe for target 'scripts/kconfig/gconf-cfg' failed
make[1]: *** [scripts/kconfig/gconf-cfg] Error 1
Makefile:567: recipe for target 'gconfig' failed
make: *** [gconfig] Error 2
$ git status
HEAD detached at v5.4
Untracked files:
(use "git add <file>..." to include in what will be committed)
scripts/kconfig/gconf-cfg.tmp
nothing added to commit but untracked files present (use "git add" to track)
This is because the check scripts are run with filechk, which misses
to clean up the temporary file on failure.
When the line
{ $(filechk_$(1)); } > $@.tmp;
... fails, it exits immediately due to the 'set -e'. Use trap to make
sure to delete the temporary file on exit.
For extra safety, I replaced $@.tmp with $(dot-target).tmp to make it
a hidden file.
Reported-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Commit bc081dd6e9 ("kbuild: generate modules.builtin") added
infrastructure to generate modules.builtin, the list of all
builtin modules.
Basically, it works like this:
- Kconfig generates include/config/tristate.conf, the list of
tristate CONFIG options with a value in a capital letter.
- scripts/Makefile.modbuiltin makes Kbuild descend into
directories to collect the information of builtin modules.
I am not a big fan of it because Kbuild ends up with traversing
the source tree twice.
I am not sure how perfectly it should work, but this approach cannot
avoid false positives; even if the relevant CONFIG option is tristate,
some Makefiles forces obj-m to obj-y.
Some examples are:
arch/powerpc/platforms/powermac/Makefile:
obj-$(CONFIG_NVRAM:m=y) += nvram.o
net/ipv6/Makefile:
obj-$(subst m,y,$(CONFIG_IPV6)) += inet6_hashtables.o
net/netlabel/Makefile:
obj-$(subst m,y,$(CONFIG_IPV6)) += netlabel_calipso.o
Nobody has complained about (or noticed) it, so it is probably fine to
have false positives in modules.builtin.
This commit simplifies the implementation. Let's exploit the fact
that every module has MODULE_LICENSE(). (modpost shows a warning if
MODULE_LICENSE is missing. If so, 0-day bot would already have blocked
such a module.)
I added MODULE_FILE to <linux/module.h>. When the code is being compiled
as builtin, it will be filled with the file path of the module, and
collected into modules.builtin.info. Then, scripts/link-vmlinux.sh
extracts the list of builtin modules out of it.
This new approach fixes the false-positives above, but adds another
type of false-positives; non-modular code may have MODULE_LICENSE()
by mistake. This is not a big deal, it is just the code is always
orphan. We can clean it up if we like. You can see cleanup examples by:
$ git log --grep='make.* explicitly non-modular'
To sum up, this commits deletes lots of code, but still produces almost
equivalent results. Please note it does not increase the vmlinux size at
all. As you can see in include/asm-generic/vmlinux.lds.h, the .modinfo
section is discarded in the link stage.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
GNU Make manual says:
$?
The names of all the prerequisites that are newer than the target,
with spaces between them.
To reflect this, rename any-prereq to newer-prereqs, which is clearer
and more intuitive.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
The incremental build of Linux kernel is pretty slow when lots of
objects are compiled. The rebuild of allmodconfig may take a few
minutes even when none of the objects needs to be rebuilt.
The time-consuming part in the incremental build is the evaluation of
if_changed* macros since they are used in the recipes to compile C and
assembly source files into objects.
I notice the following code in if_changed* is expensive:
$(filter-out $(PHONY) $(wildcard $^),$^)
In the incremental build, every object has its .*.cmd file, which
contains the auto-generated list of included headers. So, $^ are
expanded into the long list of the source file + included headers,
and $(wildcard $^) checks whether they exist.
It may not be clear why this check exists there.
Here is the record of my research.
[1] The first code addition into Kbuild
This code dates back to 2002. It is the pre-git era. So, I copy-pasted
it from the historical git tree.
| commit 4a6db0791528c220655b063cf13fefc8470dbfee (HEAD)
| Author: Kai Germaschewski <kai@tp1.ruhr-uni-bochum.de>
| Date: Mon Jun 17 00:22:37 2002 -0500
|
| kbuild: Handle removed headers
|
| New and old way to handle dependencies would choke when a file
| #include'd by other files was removed, since the dependency on it was
| still recorded, but since it was gone, make has no idea what to do about
| it (and would complain with "No rule to make <file> ...")
|
| We now add targets for all the previously included files, so make will
| just ignore them if they disappear.
|
| diff --git a/Rules.make b/Rules.make
| index 6ef827d3df39..7db5301ea7db 100644
| --- a/Rules.make
| +++ b/Rules.make
| @@ -446,7 +446,7 @@ if_changed = $(if $(strip $? \
| # execute the command and also postprocess generated .d dependencies
| # file
|
| -if_changed_dep = $(if $(strip $? \
| +if_changed_dep = $(if $(strip $? $(filter-out FORCE $(wildcard $^),$^)\
| $(filter-out $(cmd_$(1)),$(cmd_$@))\
| $(filter-out $(cmd_$@),$(cmd_$(1)))),\
| @set -e; \
| diff --git a/scripts/fixdep.c b/scripts/fixdep.c
| index b5d7bee8efc7..db45bd1888c0 100644
| --- a/scripts/fixdep.c
| +++ b/scripts/fixdep.c
| @@ -292,7 +292,7 @@ void parse_dep_file(void *map, size_t len)
| exit(1);
| }
| memcpy(s, m, p-m); s[p-m] = 0;
| - printf("%s: \\\n", target);
| + printf("deps_%s := \\\n", target);
| m = p+1;
|
| clear_config();
| @@ -314,7 +314,8 @@ void parse_dep_file(void *map, size_t len)
| }
| m = p + 1;
| }
| - printf("\n");
| + printf("\n%s: $(deps_%s)\n\n", target, target);
| + printf("$(deps_%s):\n", target);
| }
|
| void print_deps(void)
The "No rule to make <file> ..." error can be solved by passing -MP to
the compiler, but I think the detection of header removal is a good
feature. When a header is removed, all source files that previously
included it should be re-compiled. This makes sure we has correctly
got rid of #include directives of it.
This is also related with the behavior of $?. The GNU Make manual says:
$?
The names of all the prerequisites that are newer than the target,
with spaces between them.
This does not explain whether a non-existent prerequisite is considered
to be newer than the target.
At this point of time, GNU Make 3.7x was used, where the $? did not
include non-existent prerequisites. Therefore,
$(filter-out FORCE $(wildcard $^),$^)
was useful to detect the header removal, and to rebuild the related
objects if it is the case.
[2] Change of $? behavior
Later, the behavior of $? was changed (fixed) to include prerequisites
that did not exist.
First, GNU Make commit 64e16d6c00a5 ("Various changes getting ready for
the release of 3.81.") changed it, but in the release test of 3.81, it
turned out to break the kernel build.
See these:
- http://lists.gnu.org/archive/html/bug-make/2006-03/msg00003.html
- https://savannah.gnu.org/bugs/?16002
- https://savannah.gnu.org/bugs/?16051
Then, GNU Make commit 6d8d9b74d9c5 ("Numerous updates to tests for
issues found on Cygwin and Windows.") reverted it for the 3.81 release
to give Linux kernel time to adjust to the new behavior.
After the 3.81 release, GNU Make commit 7595f38f62af ("Fixed a number
of documentation bugs, plus some build/install issues:") re-added it.
[3] Adjustment to the new $? behavior on Kbuild side
Meanwhile, the kernel build was changed by commit 4f1933620f ("kbuild:
change kbuild to not rely on incorrect GNU make behavior") to adjust to
the new $? behavior.
[4] GNU Make 3.82 released in 2010
GNU Make 3.82 was the first release that integrated the correct $?
behavior. At this point, Kbuild dealt with GNU Make versions with
different $? behaviors.
3.81 or older:
$? does not contain any non-existent prerequisite.
$(filter-out $(PHONY) $(wildcard $^),$^) was useful to detect
removed include headers.
3.82 or newer:
$? contains non-existent prerequisites. When a header is removed,
it appears in $?. $(filter-out $(PHONY) $(wildcard $^),$^) became
a redundant check.
With the correct $? behavior, we could have dropped the expensive
check for 3.82 or later, but we did not. (Maybe nobody noticed this
optimization.)
[5] The .SECONDARY special target trips up $?
Some time later, I noticed $? did not work as expected under some
circumstances. As above, $? should contain non-existent prerequisites,
but the ones specified as SECONDARY do not appear in $?.
I asked this in GNU Make ML, and it seems a bug:
https://lists.gnu.org/archive/html/bug-make/2019-01/msg00001.html
Since commit 8e9b61b293 ("kbuild: move .SECONDARY special target to
Kbuild.include"), all files, including headers listed in .*.cmd files,
are treated as secondary.
So, we are back into the incorrect $? behavior.
If we Kbuild want to react to the header removal, we need to keep
$(filter-out $(PHONY) $(wildcard $^),$^) but this makes the rebuild
so slow.
[Summary]
- I believe noticing the header removal and recompiling related objects
is a nice feature for the build system.
- If $? worked correctly, $(filter-out $(PHONY),$?) would be enough
to detect the header removal.
- Currently, $? does not work correctly when used with .SECONDARY,
and Kbuild is hit by this bug.
- I filed a bug report for this, but not fixed yet as of writing.
- Currently, the header removal is detected by the following expensive
code:
$(filter-out $(PHONY) $(wildcard $^),$^)
- I do not want to revert commit 8e9b61b293 ("kbuild: move
.SECONDARY special target to Kbuild.include"). Specifying
.SECONDARY globally is clean, and it matches to the Kbuild policy.
This commit proactively removes the expensive check since it makes the
incremental build faster. A downside is Kbuild will no longer be able
to notice the header removal.
You can confirm it by the full-build followed by a header removal, and
then re-build.
$ make defconfig all
[ full build ]
$ rm include/linux/device.h
$ make
CALL scripts/checksyscalls.sh
CALL scripts/atomic/check-atomics.sh
DESCEND objtool
CHK include/generated/compile.h
Kernel: arch/x86/boot/bzImage is ready (#11)
Building modules, stage 2.
MODPOST 12 modules
Previously, Kbuild noticed a missing header and emits a build error.
Now, Kbuild is fine with it. This is an unusual corner-case, not a big
deal. Once the $? bug is fixed in GNU Make, everything will work fine.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Commit 40df759e2b ("kbuild: Fix build with binutils <= 2.19")
introduced ar-option and KBUILD_ARFLAGS to deal with old binutils.
According to Documentation/process/changes.rst, the current minimal
supported version of binutils is 2.21 so you can assume the 'D' option
is always supported. Not only GNU ar but also llvm-ar supports it.
With the 'D' option hard-coded, there is no more user of ar-option
or KBUILD_ARFLAGS.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Commit 415008af32 ("docs-rst: convert lsm from DocBook to ReST")
removed the last users of this macro.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
- remove headers_{install,check}_all targets
- remove unreasonable 'depends on !UML' from CONFIG_SAMPLES
- re-implement 'make headers_install' more cleanly
- add new header-test-y syntax to compile-test headers
- compile-test exported headers to ensure they are compilable in
user-space
- compile-test headers under include/ to ensure they are self-contained
- remove -Waggregate-return, -Wno-uninitialized, -Wno-unused-value flags
- add -Werror=unknown-warning-option for Clang
- add 128-bit built-in types support to genksyms
- fix missed rebuild of modules.builtin
- propagate 'No space left on device' error in fixdep to Make
- allow Clang to use its integrated assembler
- improve some coccinelle scripts
- add a new flag KBUILD_ABS_SRCTREE to request Kbuild to use absolute
path for $(srctree).
- do not ignore errors when compression utility is missing
- misc cleanups
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Merge tag 'kbuild-v5.3' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild
Pull Kbuild updates from Masahiro Yamada:
- remove headers_{install,check}_all targets
- remove unreasonable 'depends on !UML' from CONFIG_SAMPLES
- re-implement 'make headers_install' more cleanly
- add new header-test-y syntax to compile-test headers
- compile-test exported headers to ensure they are compilable in
user-space
- compile-test headers under include/ to ensure they are self-contained
- remove -Waggregate-return, -Wno-uninitialized, -Wno-unused-value
flags
- add -Werror=unknown-warning-option for Clang
- add 128-bit built-in types support to genksyms
- fix missed rebuild of modules.builtin
- propagate 'No space left on device' error in fixdep to Make
- allow Clang to use its integrated assembler
- improve some coccinelle scripts
- add a new flag KBUILD_ABS_SRCTREE to request Kbuild to use absolute
path for $(srctree).
- do not ignore errors when compression utility is missing
- misc cleanups
* tag 'kbuild-v5.3' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (49 commits)
kbuild: use -- separater intead of $(filter-out ...) for cc-cross-prefix
kbuild: Inform user to pass ARCH= for make mrproper
kbuild: fix compression errors getting ignored
kbuild: add a flag to force absolute path for srctree
kbuild: replace KBUILD_SRCTREE with boolean building_out_of_srctree
kbuild: remove src and obj from the top Makefile
scripts/tags.sh: remove unused environment variables from comments
scripts/tags.sh: drop SUBARCH support for ARM
kbuild: compile-test kernel headers to ensure they are self-contained
kheaders: include only headers into kheaders_data.tar.xz
kheaders: remove meaningless -R option of 'ls'
kbuild: support header-test-pattern-y
kbuild: do not create wrappers for header-test-y
kbuild: compile-test exported headers to ensure they are self-contained
init/Kconfig: add CONFIG_CC_CAN_LINK
kallsyms: exclude kasan local symbols on s390
kbuild: add more hints about SUBDIRS replacement
coccinelle: api/stream_open: treat all wait_.*() calls as blocking
coccinelle: put_device: Add a cast to an expression for an assignment
coccinelle: put_device: Adjust a message construction
...
arch/mips/Makefile passes prefixes that start with '-' to cc-cross-prefix
when $(tool-archpref) evaluates to the empty string.
They are filtered-out before the $(shell ...) invocation. Otherwise,
'command -v' would be confused.
$ command -v -linux-gcc
bash: command: -l: invalid option
command: usage: command [-pVv] command [arg ...]
Since commit 913ab9780f ("kbuild: use more portable 'command -v' for
cc-cross-prefix"), cc-cross-prefix throws away the stderr output, so
the console is not polluted in any way.
This is not a big deal in practice, but I see a slightly better taste
in adding '--' to teach it that '-linux-gcc' is an argument instead of
a command option.
This will cause extra forking of subshell, but it will not be noticeable
performance regression.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
The string returned by $(filter-out ...) does not contain any leading
or trailing spaces.
With the previous commit, 'any-prereq' no longer contains any
excessive spaces.
Nor does 'cmd-check' since it expands to a $(filter-out ...) call.
So, only the space that matters is the one between 'any-prereq'
and 'cmd-check'.
By removing it from the code, we can save $(strip ...) evaluation.
This refactoring is possible because $(any-prereq)$(cmd-check) is only
passed to the first argument of $(if ...), so we are only interested
in whether or not it is empty.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
The string returned by $(filter-out ...) does not contain any leading
or trailing spaces.
So, only the space that matters is the one between
$(filter-out $(PHONY),$?)
and
$(filter-out $(PHONY) $(wildcard $^),$^)
By removing it from the code, we can save $(strip ...) evaluation.
This refactoring is possible because $(any-prereq) is only passed to
the first argument of $(if ...), so we are only interested in whether
or not it is empty.
This is also the prerequisite for the next commit.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
I prefer 'cmd-check' for consistency.
We have 'echo-cmd', 'cmd', 'cmd_and_fixdep', etc. in this file.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Now that hdr-inst is used only in the top Makefile, move it there
from scripts/Kbuild.include.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
The kbuild documentation clearly shows that the documents
there are written at different times: some use markdown,
some use their own peculiar logic to split sections.
Convert everything to ReST without affecting too much
the author's style and avoiding adding uneeded markups.
The conversion is actually:
- add blank lines and identation in order to identify paragraphs;
- fix tables markups;
- add some lists markups;
- mark literal blocks;
- adjust title markups.
At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
To print the pathname that will be used by shell in the current
environment, 'command -v' is a standardized way. [1]
'which' is also often used in scripts, but it is less portable.
When I worked on commit bd55f96fa9 ("kbuild: refactor cc-cross-prefix
implementation"), I was eager to use 'command -v' but it did not work.
(The reason is explained below.)
I kept 'which' as before but got rid of '> /dev/null 2>&1' as I
thought it was no longer needed. Sorry, I was wrong.
It works well on my Ubuntu machine, but Alexey Brodkin reports noisy
warnings on CentOS7 when 'which' fails to find the given command in
the PATH environment.
$ which foo
which: no foo in (/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin)
Given that behavior of 'which' depends on system (and it may not be
installed by default), I want to try 'command -v' once again.
The specification [1] clearly describes the behavior of 'command -v'
when the given command is not found:
Otherwise, no output shall be written and the exit status shall reflect
that the name was not found.
However, we need a little magic to use 'command -v' from Make.
$(shell ...) passes the argument to a subshell for execution, and
returns the standard output of the command.
Here is a trick. GNU Make may optimize this by executing the command
directly instead of forking a subshell, if no shell special characters
are found in the command and omitting the subshell will not change the
behavior.
In this case, no shell special character is used. So, Make will try
to run it directly. However, 'command' is a shell-builtin command,
then Make would fail to find it in the PATH environment:
$ make ARCH=m68k defconfig
make: command: Command not found
make: command: Command not found
make: command: Command not found
In fact, Make has a table of shell-builtin commands because it must
ask the shell to execute them.
Until recently, 'command' was missing in the table.
This issue was fixed by the following commit:
| commit 1af314465e5dfe3e8baa839a32a72e83c04f26ef
| Author: Paul Smith <psmith@gnu.org>
| Date: Sun Nov 12 18:10:28 2017 -0500
|
| * job.c: Add "command" as a known shell built-in.
|
| This is not a POSIX shell built-in but it's common in UNIX shells.
| Reported by Nick Bowler <nbowler@draconx.ca>.
Because the latest release is GNU Make 4.2.1 in 2016, this commit is
not included in any released versions. (But some distributions may
have back-ported it.)
We need to trick Make to spawn a subshell. There are various ways to
do so:
1) Use a shell special character '~' as dummy
$(shell : ~; command -v $(c)gcc)
2) Use a variable reference that always expands to the empty string
(suggested by David Laight)
$(shell command$${x:+} -v $(c)gcc)
3) Use redirect
$(shell command -v $(c)gcc 2>/dev/null)
I chose 3) to not confuse people. The stderr would not be polluted
anyway, but it will provide extra safety, and is easy to understand.
Tested on Make 3.81, 3.82, 4.0, 4.1, 4.2, 4.2.1
[1] http://pubs.opengroup.org/onlinepubs/9699919799/utilities/command.html
Fixes: bd55f96fa9 ("kbuild: refactor cc-cross-prefix implementation")
Cc: linux-stable <stable@vger.kernel.org> # 5.1
Reported-by: Alexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Tested-by: Alexey Brodkin <abrodkin@synopsys.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
Reported-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
If you want to see if your linker supports a certain flag, then ask the
linker directly with ld-option (not the compiler with cc-ldoption).
Checking for linker flag support is an antipattern that complicates the
usage of various linkers other than bfd via -fuse-ld={bfd|gold|lld}.
Cc: clang-built-linux@googlegroups.com
Suggested-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
The 'addtree' and 'flags' in scripts/Kbuild.include are so compilecated
and ugly.
As I mentioned in [1], Kbuild should stop automatic prefixing of header
search path options.
I fixed up (almost) all Makefiles in the kernel. Now 'addtree' and
'flags' have been removed.
Kbuild still caters to add $(srctree)/$(src) and $(objtree)/$(obj)
to the header search path for O= building, but never touches extra
compiler options from ccflags-y etc.
[1]: https://patchwork.kernel.org/patch/9632347/
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
There is no more direct user of this macro; it is only used by
cc-ifversion.
Calling this macro is not efficient since it invokes the compiler to
get the compiler version. CONFIG_GCC_VERSION is already calculated in
the Kconfig stage, so Makefile can reuse it.
Here is a note about the slight difference between cc-version and
CONFIG_GCC_VERSION:
When using Clang, cc-version is evaluated to '0402' because Clang
defines __GNUC__ and __GNUC__MINOR__, and looks like GCC 4.2 in the
version point of view. On the other hand, CONFIG_GCC_VERSION=0
when $(CC) is clang.
There are currently two users of cc-ifversion:
arch/mips/loongson64/Platform
arch/powerpc/Makefile
They are not affected by this change.
The format of cc-version is <major><minor>, while CONFIG_GCC_VERSION
<major><minor><patch>. I adjusted cc-ifversion for the difference of
the number of digits.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
- $(word 1, <text>) is equivalent to $(firstword <text>)
- hardcode "gcc" instead of $(CC)
- minimize the shell script part
A little more notes in case $(filter-out -%, ...) is not clear.
arch/mips/Makefile passes prefixes depending on the configuration.
CROSS_COMPILE := $(call cc-cross-prefix, $(tool-archpref)-linux- \
$(tool-archpref)-linux-gnu- $(tool-archpref)-unknown-linux-gnu-)
In the Kconfig stage (e.g. when you run 'make defconfig'), neither
CONFIG_32BIT nor CONFIG_64BIT is defined. So, $(tool-archpref) is
empty. As a result, "-linux -linux-gnu- -unknown-linux-gnu" is passed
into cc-cross-prefix. The command 'which' assumes arguments starting
with a hyphen as command options, then emits the following messages:
Illegal option -l
Illegal option -l
Illegal option -u
I think it is strange to define CROSS_COMPILE depending on the CONFIG
options since you need to feed $(CC) to Kconfig, but it is how MIPS
Makefile currently works. Anyway, it would not hurt to filter-out
invalid strings beforehand.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
In Kbuild, if_changed and friends must have FORCE as a prerequisite.
Hence, $(filter-out FORCE,$^) or $(filter-out $(PHONY),$^) is a common
idiom to get the names of all the prerequisites except phony targets.
Add real-prereqs as a shorthand.
Note:
We cannot replace $(filter %.o,$^) in cmd_link_multi-m because $^ may
include auto-generated dependencies from the .*.cmd file when a single
object module is changed into a multi object module. Refer to commit
69ea912fda ("kbuild: remove unneeded link_multi_deps"). I added some
comment to avoid accidental breakage.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Rob Herring <robh@kernel.org>
Commit eea199b445 ("kbuild: remove unnecessary LEX_PREFIX and
YACC_PREFIX") removed the last users of this macro.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
You do not have to use define ... endef for filechk_* rules.
For simple cases, the use of assignment looks cleaner, IMHO.
I updated the usage for scripts/Kbuild.include in case somebody
misunderstands the 'define ... endif' is the requirement.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
filechk_* rules often consist of multiple 'echo' lines. They must be
surrounded with { } or ( ) to work correctly. Otherwise, only the
string from the last 'echo' would be written into the target.
Let's take care of that in the 'filechk' in scripts/Kbuild.include
to clean up filechk_* rules.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
In commit 54a702f705 ("kbuild: mark $(targets) as .SECONDARY and
remove .PRECIOUS markers"), I missed one important feature of the
.SECONDARY target:
.SECONDARY with no prerequisites causes all targets to be
treated as secondary.
... which agrees with the policy of Kbuild.
Let's move it to scripts/Kbuild.include, with no prerequisites.
Note:
If an intermediate file is generated by $(call if_changed,...), you
still need to add it to "targets" so its .*.cmd file is included.
The arm/arm64 crypto files are generated by $(call cmd,shipped),
so they do not need to be added to "targets", but need to be added
to "clean-files" so "make clean" can properly clean them away.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
With the change of rule_cc_o_c / rule_as_o_S in the last commit, each
command is executed in a separate subshell. Rip off unneeded semicolons.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
The 'define' ... 'endef' directive is useful to confine a series of
shell commands into a single macro:
define foo
[action1]
[action2]
[action3]
endif
Each action is executed in a separate subshell.
However, rule_cc_o_c and rule_as_o_S in scripts/Makefile.build are
written as follows (with a trailing semicolon in each cmd_*):
define rule_cc_o_c
[action1] ; \
[action2] ; \
[action3] ;
endef
All shell commands are concatenated with '; \' so that it looks like
a single command from the Makefile point of view. This does not
exploit the benefits of 'define' ... 'endef' form because a single
shell command can be more simply written, like this:
rule_cc_o_c = \
[action1] ; \
[action2] ; \
[action3] ;
I guess the intention for the command concatenation was to let the
'@set -e' in if_changed_rule cover all the commands.
We can improve the readability by moving '@set -e' to the 'cmd' macro.
The combo of $(call echo-cmd,*) $(cmd_*) in rule_cc_o_c and rule_as_o_S
have been replaced with $(call cmd,*). The trailing back-slashes have
been removed.
Here is a note about the performance: the commands in rule_cc_o_c and
rule_as_o_S were previously executed all together in a single subshell,
but now each line in a separate subshell. This means Make will spawn
extra subshells [1]. I measured the build performance for
x86_64_defconfig + CONFIG_MODVERSIONS + CONFIG_TRIM_UNUSED_KSYMS
and I saw slight performance regression, but I believe code readability
and maintainability wins.
[1] Precisely, GNU Make may optimize this by executing the command
directly instead of forking a subshell, if no shell special
characters are found in the command line and omitting the subshell
will not change the behavior.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
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>
Currently, fixdep writes dependencies to .*.tmp, which is renamed to
.*.cmd after everything succeeds. This is a very safe way to avoid
corrupted .*.cmd files. The if_changed_dep has carried this safety
mechanism since it was added in 2002.
If fixdep fails for some reasons or a user terminates the build while
fixdep is running, the incomplete output from the fixdep could be
troublesome.
This is my insight about some bad scenarios:
[1] If the compiler succeeds to generate *.o file, but fixdep fails
to write necessary dependencies to .*.cmd file, Make will miss
to rebuild the object when headers or CONFIG options are changed.
In this case, fixdep should not generate .*.cmd file at all so
that 'arg-check' will surely trigger the rebuild of the object.
[2] A partially constructed .*.cmd file may not be a syntactically
correct makefile. The next time Make runs, it would include it,
then fail to parse it. Once this happens, 'make clean' is be the
only way to fix it.
In fact, [1] is no longer a problem since commit 9c2af1c737 ("kbuild:
add .DELETE_ON_ERROR special target"). Make deletes a target file on
any failure in its recipe. Because fixdep is a part of the recipe of
*.o target, if it fails, the *.o is deleted anyway. However, I am a
bit worried about the slight possibility of [2].
So, here is a solution. Let fixdep directly write to a .*.cmd file,
but allow makefiles to include it only when its corresponding target
exists.
This effectively reverts commit 2982c95357 ("kbuild: remove redundant
$(wildcard ...) for cmd_files calculation"), and commit 00d78ab2ba
("kbuild: remove dead code in cmd_files calculation in top Makefile")
because now we must check the presence of targets.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
