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[v4,10/14] kbuild: Introduce FRAME_WARN_BUMP_FLAG

Message ID 20180711203619.1020-11-keescook@chromium.org (mailing list archive)
State Not Applicable, archived
Delegated to: Mike Snitzer
Headers show

Commit Message

Kees Cook July 11, 2018, 8:36 p.m. UTC 
When building with CONFIG_FRAME_WARN, it is sometimes useful to
give certain compilation units small additional headroom. This is
normally useful when VLA removal exposes a large stack allocation,
especially with FRAME_WARN at 1024 or smaller. This adds 20%.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 Makefile | 6 ++++++
 1 file changed, 6 insertions(+)
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Patch

diff --git a/Makefile b/Makefile
index c9132594860b..06fe93edd052 100644
--- a/Makefile
+++ b/Makefile
@@ -684,7 +684,13 @@  endif
 
 ifneq ($(CONFIG_FRAME_WARN),0)
 KBUILD_CFLAGS += $(call cc-option,-Wframe-larger-than=${CONFIG_FRAME_WARN})
+# Small code (mostly exposed by VLA removal) needs some additional
+# headroom, especially for a FRAME_WARN of 1024. This adds 20% which
+# can be used by the CFLAG_FRAME_WARN_BUMP option.
+FRAME_WARN_BUMP_SIZE := $(shell expr $(CONFIG_FRAME_WARN) / 5 + $(CONFIG_FRAME_WARN))
+FRAME_WARN_BUMP_FLAG := $(call cc-option,-Wframe-larger-than=$(FRAME_WARN_BUMP_SIZE))
 endif
+export FRAME_WARN_BUMP_FLAG
 
 stackp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector
 stackp-flags-$(CONFIG_STACKPROTECTOR)             := -fstack-protector