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kbuild: prevent CC_FLAGS_LTO self-bloating on recursive rebuilds

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CC_FLAGS_LTO gets initialized only via +=, never with := or =.
When building with CONFIG_TRIM_UNUSED_KSYMS, Kbuild may perform
several kernel rebuilds to satisfy symbol dependencies. In this
case, value of CC_FLAGS_LTO is concatenated each time, which
triggers a full rebuild.
Initialize it with := to fix this.

Fixes: dc5723b02e ("kbuild: add support for Clang LTO")
Signed-off-by: Alexander Lobakin <alobakin@pm.me>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210121184544.659998-1-alobakin@pm.me
This commit is contained in:
Alexander Lobakin 2021-01-21 18:45:55 +00:00 committed by Kees Cook
parent 112b6a8e03
commit 2b86895205
1 changed files with 2 additions and 2 deletions
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4
Makefile
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@ -895,10 +895,10 @@ endif
ifdef CONFIG_LTO_CLANG
ifdef CONFIG_LTO_CLANG_THIN
CC_FLAGS_LTO += -flto=thin -fsplit-lto-unit
CC_FLAGS_LTO := -flto=thin -fsplit-lto-unit
KBUILD_LDFLAGS += --thinlto-cache-dir=$(extmod-prefix).thinlto-cache
else
CC_FLAGS_LTO += -flto
CC_FLAGS_LTO := -flto
endif
CC_FLAGS_LTO += -fvisibility=hidden