There are people building the module with M= that's supposed to be used
for external modules. This got broken in e9aa7c285d20 ("btrfs: enable
W=1 checks for btrfs").
$ make M=fs/btrfs
scripts/Makefile.lib:10: *** Recursive variable 'KBUILD_CFLAGS' references
itself (eventually). Stop.
make: *** [Makefile:1755: modules] Error 2
There's a difference compared to 'make fs/btrfs/btrfs.ko' which needs
to rebuild a few more things and also the dependency modules need to be
available. It could fail with eg.
WARNING: Symbol version dump "Module.symvers" is missing.
Modules may not have dependencies or modversions.
In some environments it's more convenient to rebuild just the btrfs
module by M= so let's make it work.
The problem is with recursive variable evaluation in += so the
conditional C options are stored in a temporary variable to avoid the
recursion.
Signed-off-by: David Sterba <[email protected]>
---
fs/btrfs/Makefile | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/fs/btrfs/Makefile b/fs/btrfs/Makefile
index b634c42115ea..b4fb997eda16 100644
--- a/fs/btrfs/Makefile
+++ b/fs/btrfs/Makefile
@@ -7,10 +7,12 @@ subdir-ccflags-y += -Wmissing-format-attribute
subdir-ccflags-y += -Wmissing-prototypes
subdir-ccflags-y += -Wold-style-definition
subdir-ccflags-y += -Wmissing-include-dirs
-subdir-ccflags-y += $(call cc-option, -Wunused-but-set-variable)
-subdir-ccflags-y += $(call cc-option, -Wunused-const-variable)
-subdir-ccflags-y += $(call cc-option, -Wpacked-not-aligned)
-subdir-ccflags-y += $(call cc-option, -Wstringop-truncation)
+condflags := \
+ $(call cc-option, -Wunused-but-set-variable) \
+ $(call cc-option, -Wunused-const-variable) \
+ $(call cc-option, -Wpacked-not-aligned) \
+ $(call cc-option, -Wstringop-truncation)
+subdir-ccflags-y += $(condflags)
# The following turn off the warnings enabled by -Wextra
subdir-ccflags-y += -Wno-missing-field-initializers
subdir-ccflags-y += -Wno-sign-compare
--
2.29.2
