linux/scripts/Kbuild.include, branch v4.18-rc2

kbuild: remove kbuild cache

2018-05-28T18:28:58Z

The kbuild cache was introduced to remember the result of shell commands, some of which are expensive to compute, such as $(call cc-option,...). However, this turned out not so clever as I had first expected. Actually, it is problematic. For example, "$(CC) -print-file-name" is cached. If the compiler is updated, the stale search path causes build error, which is difficult to figure out. Another problem scenario is cache files could be touched while install targets are running under the root permission. We can patch them if desired, but the build infrastructure is getting uglier and uglier. Now, we are going to move compiler flag tests to the configuration phase. If this is completed, the result of compiler tests will be naturally cached in the .config file. We will not have performance issues of incremental building since this testing only happens at Kconfig time. To start this work with a cleaner code base, remove the kbuild cache first. Revert the following commits: Commit 9a234a2e3843 ("kbuild: create directory for make cache only when necessary") Commit e17c400ae194 ("kbuild: shrink .cache.mk when it exceeds 1000 lines") Commit 4e56207130ed ("kbuild: Cache a few more calls to the compiler") Commit 3298b690b21c ("kbuild: Add a cache for generated variables") Signed-off-by: Masahiro Yamada Reviewed-by: Kees Cook

kbuild: do not display CHK for filechk

2018-05-28T09:25:21Z

filechk displays two short logs; CHK for creating a temporary file, and UPD for really updating the target. IMHO, the build system can be quiet when the target file has not been updated. Signed-off-by: Masahiro Yamada Reviewed-by: Sam Ravnborg

Kbuild: fix # escaping in .cmd files for future Make

2018-04-10T15:03:02Z

I tried building using a freshly built Make (4.2.1-69-g8a731d1), but already the objtool build broke with orc_dump.c: In function ‘orc_dump’: orc_dump.c:106:2: error: ‘elf_getshnum’ is deprecated [-Werror=deprecated-declarations] if (elf_getshdrnum(elf, &nr_sections)) { Turns out that with that new Make, the backslash was not removed, so cpp didn't see a #include directive, grep found nothing, and -DLIBELF_USE_DEPRECATED was wrongly put in CFLAGS. Now, that new Make behaviour is documented in their NEWS file: * WARNING: Backward-incompatibility! Number signs (#) appearing inside a macro reference or function invocation no longer introduce comments and should not be escaped with backslashes: thus a call such as: foo := $(shell echo '#') is legal. Previously the number sign needed to be escaped, for example: foo := $(shell echo '\#') Now this latter will resolve to "\#". If you want to write makefiles portable to both versions, assign the number sign to a variable: C := \# foo := $(shell echo '$C') This was claimed to be fixed in 3.81, but wasn't, for some reason. To detect this change search for 'nocomment' in the .FEATURES variable. This also fixes up the two make-cmd instances to replace # with $(pound) rather than with \#. There might very well be other places that need similar fixup in preparation for whatever future Make release contains the above change, but at least this builds an x86_64 defconfig with the new make. Link: https://bugzilla.kernel.org/show_bug.cgi?id=197847 Cc: Randy Dunlap Signed-off-by: Rasmus Villemoes Signed-off-by: Masahiro Yamada

kbuild: move include/config/ksym/* to include/ksym/*

2018-03-25T17:01:23Z

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 Acked-by: Nicolas Pitre

kbuild: simplify ld-option implementation

2018-03-25T17:01:20Z

Currently, linker options are tested by the coordination of $(CC) and $(LD) because $(LD) needs some object to link. As commit 86a9df597cdd ("kbuild: fix linker feature test macros when cross compiling with Clang") addressed, we need to make sure $(CC) and $(LD) agree the underlying architecture of the passed object. This could be a bit complex when we combine tools from different groups. For example, we can use clang for $(CC), but we still need to rely on GCC toolchain for $(LD). So, I was searching for a way of standalone testing of linker options. A trick I found is to use '-v'; this not only prints the version string, but also tests if the given option is recognized. If a given option is supported, $ aarch64-linux-gnu-ld -v --fix-cortex-a53-843419 GNU ld (Linaro_Binutils-2017.11) 2.28.2.20170706 $ echo $? 0 If unsupported, $ aarch64-linux-gnu-ld -v --fix-cortex-a53-843419 GNU ld (crosstool-NG linaro-1.13.1-4.7-2013.04-20130415 - Linaro GCC 2013.04) 2.23.1 aarch64-linux-gnu-ld: unrecognized option '--fix-cortex-a53-843419' aarch64-linux-gnu-ld: use the --help option for usage information $ echo $? 1 Gold works likewise. $ aarch64-linux-gnu-ld.gold -v --fix-cortex-a53-843419 GNU gold (Linaro_Binutils-2017.11 2.28.2.20170706) 1.14 masahiro@pug:~/ref/linux$ echo $? 0 $ aarch64-linux-gnu-ld.gold -v --fix-cortex-a53-999999 GNU gold (Linaro_Binutils-2017.11 2.28.2.20170706) 1.14 aarch64-linux-gnu-ld.gold: --fix-cortex-a53-999999: unknown option aarch64-linux-gnu-ld.gold: use the --help option for usage information $ echo $? 1 LLD too. $ ld.lld -v --gc-sections LLD 7.0.0 (http://llvm.org/git/lld.git 4a0e4190e74cea19f8a8dc625ccaebdf8b5d1585) (compatible with GNU linkers) $ echo $? 0 $ ld.lld -v --fix-cortex-a53-843419 LLD 7.0.0 (http://llvm.org/git/lld.git 4a0e4190e74cea19f8a8dc625ccaebdf8b5d1585) (compatible with GNU linkers) $ echo $? 0 $ ld.lld -v --fix-cortex-a53-999999 ld.lld: error: unknown argument: --fix-cortex-a53-999999 LLD 7.0.0 (http://llvm.org/git/lld.git 4a0e4190e74cea19f8a8dc625ccaebdf8b5d1585) (compatible with GNU linkers) $ echo $? 1 Signed-off-by: Masahiro Yamada Tested-by: Nick Desaulniers

kbuild: Improve portability of some sed invocations

2018-03-25T17:01:18Z

* Use BREs where EREs aren't necessary. * Pass -E instead of -r to use EREs. This will be standardized in the next POSIX revision[0]. GNU sed supports this since 4.2 (May 2009), and busybox since 1.22.0 (Jan 2014). * Use the [:space:] character class instead of ` \t` in bracket expressions. In bracket expressions, POSIX says that loses its special meaning, so a conforming implementation cannot expand \t to [1]. * In BREs, use interval expressions (\{n,m\}) instead of non-standard features like \+ and \?. * Use a loop instead of -s flag. There are still plenty of other cases of non-standard sed invocations (use of ERE features in BREs, in-place editing), but this fixes some core ones. [0] http://austingroupbugs.net/view.php?id=528 [1] http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html#tag_09_03_05 Signed-off-by: Michael Forney Signed-off-by: Masahiro Yamada

kbuild: create directory for make cache only when necessary

2017-11-16T00:07:32Z

Currently, the existence of $(dir $(make-cache)) is always checked, and created if it is missing. We can avoid unnecessary system calls by some tricks. [1] If KBUILD_SRC is unset, we are building in the source tree. The output directory checks can be entirely skipped. [2] If at least one cache data is found, it means the cache file was included. Obviously its directory exists. Skip "mkdir -p". [3] If Makefile does not contain any call of __run-and-store, it will not create a cache file. No need to create its directory. [4] The "mkdir -p" should be only invoked by the first call of __run-and-store Signed-off-by: Masahiro Yamada Reviewed-by: Douglas Anderson

kbuild: fix linker feature test macros when cross compiling with Clang

2017-11-13T13:54:24Z

I was not seeing my linker flags getting added when using ld-option when cross compiling with Clang. Upon investigation, this seems to be due to a difference in how GCC vs Clang handle cross compilation. GCC is configured at build time to support one backend, that is implicit when compiling. Clang is explicit via the use of `-target ` and ships with all supported backends by default. GNU Make feature test macros that compile then link will always fail when cross compiling with Clang unless Clang's triple is passed along to the compiler. For example: $ clang -x c /dev/null -c -o temp.o $ aarch64-linux-android/bin/ld -E temp.o aarch64-linux-android/bin/ld: unknown architecture of input file `temp.o' is incompatible with aarch64 output aarch64-linux-android/bin/ld: warning: cannot find entry symbol _start; defaulting to 0000000000400078 $ echo $? 1 $ clang -target aarch64-linux-android- -x c /dev/null -c -o temp.o $ aarch64-linux-android/bin/ld -E temp.o aarch64-linux-android/bin/ld: warning: cannot find entry symbol _start; defaulting to 00000000004002e4 $ echo $? 0 This causes conditional checks that invoke $(CC) without the target triple, then $(LD) on the result, to always fail. Suggested-by: Masahiro Yamada Signed-off-by: Nick Desaulniers Reviewed-by: Matthias Kaehlcke Signed-off-by: Masahiro Yamada

kbuild: shrink .cache.mk when it exceeds 1000 lines

2017-11-13T13:54:24Z

The cache files are only cleaned away by "make clean". If you continue incremental builds, the cache files will grow up little by little. It is not a big deal in general use cases because compiler flags do not change quite often. However, if you do build-test for various architectures, compilers, and kernel configurations, you will end up with huge cache files soon. When the cache file exceeds 1000 lines, shrink it down to 500 by "tail". The Least Recently Added lines are cut. (not Least Recently Used) I hope it will work well enough. Signed-off-by: Masahiro Yamada Reviewed-by: Douglas Anderson

kbuild: Add a cache for generated variables

2017-11-13T13:54:23Z

While timing a "no-op" build of the kernel (incrementally building the kernel even though nothing changed) in the Chrome OS build system I found that it was much slower than I expected. Digging into things a bit, I found that quite a bit of the time was spent invoking the C compiler even though we weren't actually building anything. Currently in the Chrome OS build system the C compiler is called through a number of wrappers (one of which is written in python!) and can take upwards of 100 ms to invoke even if we're not doing anything difficult, so these invocations of the compiler were taking a lot of time. Worse the invocations couldn't seem to take advantage of the multiple cores on my system. Certainly it seems like we could make the compiler invocations in the Chrome OS build system faster, but only to a point. Inherently invoking a program as big as a C compiler is a fairly heavy operation. Thus even if we can speed the compiler calls it made sense to track down what was happening. It turned out that all the compiler invocations were coming from usages like this in the kernel's Makefile: KBUILD_CFLAGS += $(call cc-option,-fno-delete-null-pointer-checks,) Due to the way cc-option and similar statements work the above contains an implicit call to the C compiler. ...and due to the fact that we're storing the result in KBUILD_CFLAGS, a simply expanded variable, the call will happen every time the Makefile is parsed, even if there are no users of KBUILD_CFLAGS. Rather than redoing this computation every time, it makes a lot of sense to cache the result of all of the Makefile's compiler calls just like we do when we compile a ".c" file to a ".o" file. Conceptually this is quite a simple idea. ...and since the calls to invoke the compiler and similar tools are centrally located in the Kbuild.include file this doesn't even need to be super invasive. Implementing the cache in a simple-to-use and efficient way is not quite as simple as it first sounds, though. To get maximum speed we really want the cache in a format that make can natively understand and make doesn't really have an ability to load/parse files. ...but make _can_ import other Makefiles, so the solution is to store the cache in Makefile format. This requires coming up with a valid/unique Makefile variable name for each value to be cached, but that's solvable with some cleverness. After this change, we'll automatically create a ".cache.mk" file that will contain our cached variables. We'll load this on each invocation of make and will avoid recomputing anything that's already in our cache. The cache is stored in a format that it shouldn't need any invalidation since anything that might change should affect the "key" and any old cached value won't be used. Signed-off-by: Douglas Anderson Tested-by: Ingo Molnar Tested-by: Guenter Roeck Signed-off-by: Masahiro Yamada