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Date: Thu, 12 May 2022 01:45:11 +0900 From: Masahiro Yamada <masahiroy@...nel.org> To: linux-kbuild@...r.kernel.org Cc: linux-kernel@...r.kernel.org, Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, Nicolas Schier <nicolas@...sle.eu>, Peter Zijlstra <peterz@...radead.org>, linux-modules@...r.kernel.org, llvm@...ts.linux.dev, Ard Biesheuvel <ardb@...nel.org>, Sami Tolvanen <samitolvanen@...gle.com>, Masahiro Yamada <masahiroy@...nel.org> Subject: [PATCH v5 09/12] kbuild: make built-in.a rule robust against too long argument error Kbuild runs at the top of objtree instead of changing the working directory to subdirectories. I think this design is nice overall but some commands have a scalability issue. The build command of built-in.a is one of them whose length scales with: O(D * N) Here, D is the length of the directory path (i.e. $(obj)/ prefix), N is the number of objects in the Makefile, O() is the big O notation. The deeper directory the Makefile directory is located, the more easily it will hit the too long argument error. We can make it better. Trim the $(obj)/ by Make's builtin function, and restore it by a shell command (sed). With this, the command length scales with: O(D + N) In-tree modules still have some room to the limit (ARG_MAX=2097152), but this is more future-proof for big modules in a deep directory. For example, you can build i915 as builtin (CONFIG_DRM_I915=y) and compare drivers/gpu/drm/i915/.built-in.a.cmd with/without this commit. Signed-off-by: Masahiro Yamada <masahiroy@...nel.org> Reviewed-by: Nicolas Schier <nicolas@...sle.eu> Tested-by: Nathan Chancellor <nathan@...nel.org> --- (no changes since v2) Changes in v2: - New patch scripts/Makefile.build | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/scripts/Makefile.build b/scripts/Makefile.build index c2a173b3fd60..8f1a355df7aa 100644 --- a/scripts/Makefile.build +++ b/scripts/Makefile.build @@ -374,7 +374,10 @@ $(subdir-modorder): $(obj)/%/modules.order: $(obj)/% ; # quiet_cmd_ar_builtin = AR $@ - cmd_ar_builtin = rm -f $@; $(AR) cDPrST $@ $(real-prereqs) + cmd_ar_builtin = rm -f $@; \ + echo $(patsubst $(obj)/%,%,$(real-prereqs)) | \ + sed -E 's:([^ ]+):$(obj)/\1:g' | \ + xargs $(AR) cDPrST $@ $(obj)/built-in.a: $(real-obj-y) FORCE $(call if_changed,ar_builtin) -- 2.32.0
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