kbuild: prevent exported headers from including <stdlib.h>, <stdbool.h>

Some UAPI headers included <stdlib.h>, like this: #ifndef __KERNEL__ #include <stdlib.h> #endif As it turned out, they just included it for no good reason. After some fixes, now I can compile-test UAPI headers (CONFIG_UAPI_HEADER_TEST=y) without including <stdlib.h> from the system header search paths. To avoid somebody getting it back again, this commit adds the dummy header, usr/dummy-include/stdlib.h I added $(srctree)/usr/dummy-include to the header search paths. Because it is searched before the system directories, if someone tries to include <stdlib.h>, they will see the error message. While I am here, I also replaced $(objtree)/usr/include with $(obj), but it has no functional change. If we can make kernel headers self-contained (that is, none of exported kernel headers includes system headers), we will be able to add the -nostdinc flag, but that is much far from where we stand now. As a realistic solution, we can ban header inclusion individually by putting a dummy header into usr/dummy-include/. Currently, no header include <stdbool.h>. I put it as well before somebody attempts to use it. Signed-off-by: Masahiro Yamada <[email protected]> Signed-off-by: Arnd Bergmann <[email protected]> Reviewed-by: Greg Kroah-Hartman <[email protected]>
torvalds · May 13, 2022 · 02a6e4b · 02a6e4b
1 parent 783eb35
commit 02a6e4b
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Showing 3 changed files with 15 additions and 1 deletion.
diff --git a/usr/dummy-include/stdbool.h b/usr/dummy-include/stdbool.h
@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _STDBOOL_H
+#define _STDBOOL_H
+
+#error "Please do not include <stdbool.h> from exported headers"
+
+#endif /* _STDBOOL_H */
diff --git a/usr/dummy-include/stdlib.h b/usr/dummy-include/stdlib.h
@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _STDLIB_H
+#define _STDLIB_H
+
+#error "Please do not include <stdlib.h> from exported headers"
+
+#endif /* _STDLIB_H */
diff --git a/usr/include/Makefile b/usr/include/Makefile
@@ -15,7 +15,7 @@ UAPI_CFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CFLAGS))
 # USERCFLAGS might contain sysroot location for CC.
 UAPI_CFLAGS += $(USERCFLAGS)
 
-override c_flags = $(UAPI_CFLAGS) -Wp,-MMD,$(depfile) -I$(objtree)/usr/include
+override c_flags = $(UAPI_CFLAGS) -Wp,-MMD,$(depfile) -I $(obj) -I $(srctree)/usr/dummy-include
 
 # The following are excluded for now because they fail to build.
 #