user/sven/linux.git/scripts/Kbuild.include, branch v4.15.9

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

kbuild: trivial cleanups on the comments

2017-08-09T15:58:20Z

This is a bunch of trivial fixes and cleanups. Signed-off-by: Cao jin Signed-off-by: Masahiro Yamada

kbuild: Add __cc-option macro

2017-06-25T03:47:55Z

cc-option uses KBUILD_CFLAGS and KBUILD_CPPFLAGS when it determines whether an option is supported or not. This is fine for options used to build the kernel itself, however some components like the x86 boot code use a different set of flags. Add the new macro __cc-option which is a more generic version of cc-option with additional parameters. One parameter is the compiler with which the check should be performed, the other the compiler options to be used instead KBUILD_C*FLAGS. Refactor cc-option and hostcc-option to use __cc-option and move hostcc-option to scripts/Kbuild.include. Suggested-by: Arnd Bergmann Suggested-by: Masahiro Yamada Signed-off-by: Matthias Kaehlcke Acked-by: Arnd Bergmann Acked-by: Michal Marek Signed-off-by: Masahiro Yamada

kbuild: remove cc-option-align

2017-06-25T03:43:00Z

Documentation/kbuild/makefiles.txt says the change for align options occurred at GCC 3.0, and Documentation/process/changes.rst says the minimal supported GCC version is 3.2, so it should be safe to hard-code -falign* options. Fix the only user arch/x86/Makefile_32.cpu and remove cc-option-align. Signed-off-by: Masahiro Yamada Acked-by: Ingo Molnar

Merge tag 'kbuild-v4.12' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild

2017-05-11T03:11:05Z

Pull Kbuild updates from Masahiro Yamada: - improve Clang support - clean up various Makefiles - improve build log visibility (objtool, alpha, ia64) - improve compiler flag evaluation for better build performance - fix GCC version-dependent warning - fix genksyms * tag 'kbuild-v4.12' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (23 commits) kbuild: dtbinst: remove unnecessary __dtbs_install_prep target ia64: beatify build log for gate.so and gate-syms.o alpha: make short build log available for division routines alpha: merge build rules of division routines alpha: add $(src)/ rather than $(obj)/ to make source file path Makefile: evaluate LDFLAGS_BUILD_ID only once objtool: make it visible in make V=1 output kbuild: clang: add -no-integrated-as to KBUILD_[AC]FLAGS kbuild: Add support to generate LLVM assembly files kbuild: Add better clang cross build support kbuild: drop -Wno-unknown-warning-option from clang options kbuild: fix asm-offset generation to work with clang kbuild: consolidate redundant sed script ASM offset generation frv: Use OFFSET macro in DEF_*REG() kbuild: avoid conflict between -ffunction-sections and -pg on gcc-4.7 kbuild: Consolidate header generation from ASM offset information kbuild: use -Oz instead of -Os when using clang kbuild, LLVMLinux: Add -Werror to cc-option to support clang Kbuild: make designated_init attribute fatal kbuild: drop unneeded patterns '.*.orig' and '.*.rej' from distclean ...

kbuild, LLVMLinux: Add -Werror to cc-option to support clang

2017-04-11T19:34:20Z

Clang will warn about unknown warnings but will not return false unless -Werror is set. GCC will return false if an unknown warning is passed. Adding -Werror make both compiler behave the same. [arnd: it turns out we need the same patch for testing whether -ffunction-sections works right with gcc. I've build tested extensively with this patch applied, so let's just merge this one now.] Signed-off-by: Mark Charlebois Signed-off-by: Behan Webster Reviewed-by: Jan-Simon Möller Signed-off-by: Arnd Bergmann Acked-by: Kees Cook Signed-off-by: Masahiro Yamada

x86/build: Mostly disable '-maccumulate-outgoing-args'

2017-03-30T09:53:04Z

The GCC '-maccumulate-outgoing-args' flag is enabled for most configs, mostly because of issues which are no longer relevant. For most configs, and with most recent versions of GCC, it's no longer needed. Clarify which cases need it, and only enable it for those cases. Also produce a compile-time error for the ftrace graph + mcount + '-Os' case, which will otherwise cause runtime failures. The main benefit of '-maccumulate-outgoing-args' is that it prevents an ugly prologue for functions which have aligned stacks. But removing the option also has some benefits: more readable argument saves, smaller text size, and (presumably) slightly improved performance. Here are the object size savings for 32-bit and 64-bit defconfig kernels: text data bss dec hex filename 10006710 3543328 1773568 15323606 e9d1d6 vmlinux.x86-32.before 9706358 3547424 1773568 15027350 e54c96 vmlinux.x86-32.after text data bss dec hex filename 10652105 4537576 843776 16033457 f4a6b1 vmlinux.x86-64.before 10639629 4537576 843776 16020981 f475f5 vmlinux.x86-64.after That comes out to a 3% text size improvement on x86-32 and a 0.1% text size improvement on x86-64. Signed-off-by: Josh Poimboeuf Cc: Andrew Lutomirski Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: Linus Torvalds Cc: Pavel Machek Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20170316193133.zrj6gug53766m6nn@treble Signed-off-by: Ingo Molnar