pm24.git/scripts/Kbuild.include, branch v6.2-rc3

kbuild: use .NOTINTERMEDIATE for future GNU Make versions

2022-12-13T13:29:10Z

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is an intermediate file, then make can leave well enough alone: it won't create 'b' unless one of its prerequisites is out of date.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 54a702f70589 ("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 . [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 | ^~~~~~~~~~~~~~~~ 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 , and rebuilds objects that depended on . There exists a source file that includes , and it raises an error. To see detailed background information, refer to commit 2d3b1b8f0da7 ("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

kbuild: add read-file macro

2022-12-13T13:29:10Z

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 Reviewed-by: Nicolas Schier Reviewed-by: Alexander Lobakin Tested-by: Alexander Lobakin

kbuild: add test-{ge,gt,le,lt} macros

2022-12-13T13:21:14Z

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 Acked-by: Palmer Dabbelt # RISC-V Reviewed-by: Nathan Chancellor Reviewed-by: Nicolas Schier

kbuild: add kbuild-file macro

2022-11-22T14:40:02Z

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 Reviewed-by: Nicolas Schier Reviewed-by: Alexander Lobakin Tested-by: Alexander Lobakin

kbuild: remove the target in signal traps when interrupted

2022-09-28T17:00:29Z

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 392885ee82d3 ("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. > $(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 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: 392885ee82d3 ("kbuild: let fixdep directly write to .*.cmd files") Reported-by: Ingo Molnar Reported-by: Rob Herring Signed-off-by: Masahiro Yamada Tested-by: Ingo Molnar Reviewed-by: Nicolas Schier

kbuild: add cmd_and_savecmd macro

2022-06-01T14:07:29Z

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 Reviewed-by: Kees Cook Tested-by: Nathan Chancellor Reviewed-by: Nicolas Schier Tested-by: Sedat Dilek # LLVM-14 (x86-64)

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

2022-05-29T09:39:35Z

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 Reviewed-by: Nicolas Schier Tested-by: Nathan Chancellor Reviewed-by: Sami Tolvanen Tested-by: Sedat Dilek # LLVM-14 (x86-64) Acked-by: Josh Poimboeuf

certs: simplify $(srctree)/ handling and remove config_filename macro

2022-01-08T08:46:35Z

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

kbuild: warn if FORCE is missing for if_changed(_dep,_rule) and filechk

2021-09-02T23:17:19Z

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 Tested-by: Nicolas Schier

kbuild: macrofy the condition of if_changed and friends

2021-09-02T23:17:19Z

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