* [PATCH 1/2] kbuild: Require a 'make clean' if we detect gcc changed underneath us
2017-12-22 1:53 [PATCH 0/2] kbuild: Fix corner caches with .cache.mk Douglas Anderson
@ 2017-12-22 1:53 ` Douglas Anderson
2017-12-22 1:53 ` [PATCH 2/2] kbuild: Don't mess with the .cache.mk when installing Douglas Anderson
1 sibling, 0 replies; 3+ messages in thread
From: Douglas Anderson @ 2017-12-22 1:53 UTC (permalink / raw)
To: Masahiro Yamada
Cc: malat, dave.hansen, yang.s, linux, Douglas Anderson,
Matthias Kaehlcke, Cao jin, Arnd Bergmann, Mark Charlebois,
linux-kernel, Josh Poimboeuf, Ingo Molnar
Several people reported that the commit 3298b690b21c ("kbuild: Add a
cache for generated variables") caused them problems when they updated
gcc versions. Specifically the reports all looked something similar
to this:
> In file included from ./include/uapi/linux/uuid.h:21:0,
> from ./include/linux/uuid.h:19,
> from ./include/linux/mod_devicetable.h:12,
> from scripts/mod/devicetable-offsets.c:2:
> ./include/linux/string.h:8:20: fatal error: stdarg.h: No such file or
> directory
> #include <stdarg.h>
Masahiro Yamada determined that the problem was with:
NOSTDINC_FLAGS += -nostdinc -isystem $(call shell-cached,$(CC)
-print-file-name=include)
Specifically that the stale result of -print-file-name is stored in
the cache file. It was determined that a "make clean" fixed the
problems in all cases.
In this particular case we could certainly try to clean just the cache
when we detect a gcc update, but it seems like overall it's a bad idea
to do an incremental build when gcc changes. We should warn the user
and tell them that they need a 'make clean'.
Fixes: 3298b690b21c ("kbuild: Add a cache for generated variables")
Reported-by: Yang Shi <yang.s@alibaba-inc.com>
Reported-by: Dave Hansen <dave.hansen@intel.com>
Reported-by: Mathieu Malaterre <malat@debian.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
---
scripts/Kbuild.include | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 065324a8046f..56dee20fb2b8 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -222,6 +222,10 @@ cc-version = $(call shell-cached,$(CONFIG_SHELL) $(srctree)/scripts/gcc-version.
cc-fullversion = $(call shell-cached,$(CONFIG_SHELL) \
$(srctree)/scripts/gcc-version.sh -p $(CC))
+# cc-fullversion-uncached
+cc-fullversion-uncached := $(shell $(CONFIG_SHELL) \
+ $(srctree)/scripts/gcc-version.sh -p $(CC))
+
# cc-ifversion
# Usage: EXTRA_CFLAGS += $(call cc-ifversion, -lt, 0402, -O1)
cc-ifversion = $(shell [ $(cc-version) $(1) $(2) ] && echo $(3) || echo $(4))
@@ -475,3 +479,14 @@ endif
endef
#
###############################################################################
+
+# Require a 'make clean' if the compiler changed; not only does the .cache.mk
+# need to be thrown out but we should also start with fresh object files.
+#
+# NOTE: it's important that we don't error out when the goal is actually to
+# try to make clean, distclean or mrproper.
+ifeq ($(filter %clean,$(MAKECMDGOALS))$(filter mrproper,$(MAKECMDGOALS)),)
+ ifneq ($(cc-fullversion-uncached),$(cc-fullversion))
+ $(error Detected new CC version ($(cc-fullversion-uncached) vs $(cc-fullversion)). Please 'make clean')
+ endif
+endif
--
2.15.1.620.gb9897f4670-goog
^ permalink raw reply [flat|nested] 3+ messages in thread* [PATCH 2/2] kbuild: Don't mess with the .cache.mk when installing
2017-12-22 1:53 [PATCH 0/2] kbuild: Fix corner caches with .cache.mk Douglas Anderson
2017-12-22 1:53 ` [PATCH 1/2] kbuild: Require a 'make clean' if we detect gcc changed underneath us Douglas Anderson
@ 2017-12-22 1:53 ` Douglas Anderson
1 sibling, 0 replies; 3+ messages in thread
From: Douglas Anderson @ 2017-12-22 1:53 UTC (permalink / raw)
To: Masahiro Yamada
Cc: malat, dave.hansen, yang.s, linux, Douglas Anderson,
Matthias Kaehlcke, Cao jin, Arnd Bergmann, Marcin Nowakowski,
Mark Charlebois, linux-kernel, Josh Poimboeuf, Ingo Molnar
As pointed out by Masahiro Yamada people often run "sudo make install"
or "sudo make modules_install". In theory, that could cause a cache
file (or the directory containing it) to be created by root. After
doing this then subsequent invocations to make would yell with a whole
bunch of warnings like:
/bin/sh: ./.cache.mk: Permission denied
These yells would be mostly harmless (we'd just go on running without
the cache), but they're ugly.
The above situation would be fairly unlikely because it should only
happen if someone does "sudo make install" before doing a normal
"make", which is an invalid thing to do. If you did a normal "make"
before the "sudo make install" then all the cache files and
directories should have already been created by a normal user and,
even if the superuser needed to add to the existing files, we wouldn't
end up with a permission problem.
The above situation would also not have been catastrophic because
presumably if the user was able to run "sudo make install" then they
should also be able to run "sudo make clean" to clean things up.
However, even though the problem described is relatively minor, it
probably makes sense to add a heuristic to avoid creating cache files
when one of the make goals looks like an install. This heuristic
doesn't add a ton of overhead and it might save someone time tracking
down strange "Permission denied" messages. We'll consider this
heuristic good enough because the problem really shouldn't be that
serious.
Fixes: 3298b690b21c ("kbuild: Add a cache for generated variables")
Suggested-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
---
scripts/Kbuild.include | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 56dee20fb2b8..e18235cd9570 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -124,6 +124,12 @@ __sanitize-opt = $(subst $$,_,$(subst $(right_paren),_,$(subst $(left_paren),_,$
# previous invocation of make!) we'll return the value. If not, we'll
# compute it and store the result for future runs.
#
+# NOTE: we won't ever add to the cache if one of the make goals looks like
+# it is installing. Technically there's no reason we can't cache things
+# related to install but it's likely that 'make install' is called as root.
+# If we create the cache file as root we might have a hard time adding to it
+# (or deleting it in make clean).
+#
# This is a bit of voodoo, but basic explanation is that if the variable
# was undefined then we'll evaluate the shell command and store the result
# into the variable. We'll then store that value in the cache and finally
@@ -137,12 +143,14 @@ __sanitize-opt = $(subst $$,_,$(subst $(right_paren),_,$(subst $(left_paren),_,$
define __run-and-store
ifeq ($(origin $(1)),undefined)
$$(eval $(1) := $$(shell $$(2)))
+ifeq ($(filter %install,$(MAKECMDGOALS)),)
ifeq ($(create-cache-dir),1)
$$(shell mkdir -p $(dir $(make-cache)))
$$(eval create-cache-dir :=)
endif
$$(shell echo '$(1) := $$($(1))' >> $(make-cache))
endif
+endif
endef
__shell-cached = $(eval $(call __run-and-store,$(1)))$($(1))
shell-cached = $(call __shell-cached,__cached_$(call __sanitize-opt,$(1)),$(1))
--
2.15.1.620.gb9897f4670-goog
^ permalink raw reply [flat|nested] 3+ messages in thread