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authorMasahiro Yamada <masahiroy@kernel.org>2022-05-27 13:01:52 +0300
committerMasahiro Yamada <masahiroy@kernel.org>2022-06-01 17:07:29 +0300
commitcd968b97c49214e6557381bddddacbd0e0fb696e (patch)
treec7df9e88fd1767e7e335ea3ab0104d9fdde163b4 /scripts/Makefile.build
parent31cb50b5590fe911077b8463ad01144fac8fa4f3 (diff)
downloadlinux-cd968b97c49214e6557381bddddacbd0e0fb696e.tar.xz
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@kernel.org> Reviewed-by: Nicolas Schier <nicolas@fjasle.eu> Tested-by: Nathan Chancellor <nathan@kernel.org> Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # LLVM-14 (x86-64)
Diffstat (limited to 'scripts/Makefile.build')
-rw-r--r--scripts/Makefile.build7
1 files changed, 6 insertions, 1 deletions
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index b6ae652a943f..3c1e20e4a4fc 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -377,9 +377,14 @@ $(subdir-modorder): $(obj)/%/modules.order: $(obj)/% ;
#
# Rule to compile a set of .o files into one .a file (without symbol table)
#
+# To make this rule robust against "Argument list too long" error,
+# remove $(obj)/ prefix, and restore it by a shell command.
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)