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authorMasahiro Yamada <yamada.masahiro@socionext.com>2018-03-16 08:37:15 +0100
committerMasahiro Yamada <yamada.masahiro@socionext.com>2018-03-25 19:01:24 +0200
commit3fdc7d3fe4c04bab0305838cf662ae30051cc192 (patch)
tree358ae9df059dd8ca0321dfb6c9d7088be3e8d81b /arch/powerpc/boot
parentkbuild: move include/config/ksym/* to include/ksym/* (diff)
downloadlinux-3fdc7d3fe4c04bab0305838cf662ae30051cc192.tar.xz
linux-3fdc7d3fe4c04bab0305838cf662ae30051cc192.zip
kbuild: link vmlinux only once for CONFIG_TRIM_UNUSED_KSYMS
If CONFIG_TRIM_UNUSED_KSYMS is enabled and the kernel is built from a pristine state, the vmlinux is linked twice. [1] A user runs 'make' [2] First build with empty autoksyms.h [3] adjust_autoksyms.sh updates autoksyms.h and recurses 'make vmlinux' --------(begin sub-make)-------- [4] Second build with new autoksyms.h [5] link-vmlinux.sh is invoked because vmlinux is missing ---------(end sub-make)--------- [6] link-vmlinux.sh is invoked again despite vmlinux is up-to-date. The reason of [6] is probably because Make already decided to update vmlinux at the time of [2] because vmlinux was missing when Make built up the dependency graph. Because if_changed is implemented based on $?, this issue can be narrowed down to how Make handles $?. You can test it with the following simple code: [Test Makefile] A: B @echo newer prerequisite: $? cp B A B: C cp C B touch A [Result] $ rm -f A B $ touch C $ make cp C B touch A newer prerequisite: B cp B A Here, 'A' has been touched in the recipe of 'B'. So, the dependency 'A: B' has already been met before the recipe of 'A' is executed. However, Make does not notice the fact that the recipe of 'B' also updates 'A' as a side-effect. The situation is similar in this case; the vmlinux has actually been updated in the vmlinux_prereq target. Make cannot predict this, so judges the vmlinux is old. link-vmlinux.sh is costly, so it is better to not run it when unneeded. Split CONFIG_TRIM_UNUSED_KSYMS recursion to a dedicated target. The reason of commit 2441e78b1919 ("kbuild: better abstract vmlinux sequential prerequisites") was to cater to CONFIG_BUILD_DOCSRC, but it was later removed by commit 184892925118 ("samples: move blackfin gptimers-example from Documentation"). Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com> Acked-by: Nicolas Pitre <nico@linaro.org>
Diffstat (limited to 'arch/powerpc/boot')
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