kbuild: introduce __init_refok/__initdata_refok to supress section mismatch warnings

Throughout the kernel there are a few legitimite references
to init or exit sections. Most of these are covered by the
patterns included in modpost but a few nees special attention.
To avoid hardcoding a lot of function names in modpost introduce
a marker so relevant function/data can be marked.
When modpost see a reference to a init/exit function from
a function/data marked no warning will be issued.

Idea from: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Andrew Morton <akpm@linux-foundation.org>

2 files changed, 17 insertions, 2 deletions

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 52e2d69ee535..8307b1bb337a 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -11,7 +11,8 @@
 
 /* .data section */
 #define DATA_DATA                                                       \
-        *(.data)
+        *(.data)                                                        \
+        *(.data.init.refok)
 
 #define RODATA                                                          \
         . = ALIGN(4096);                                                \
@@ -147,7 +148,8 @@
  * during second ld run in second ld pass when generating System.map */
 #define TEXT_TEXT                                                       \
                 ALIGN_FUNCTION();                                       \
-                *(.text)
+                *(.text)                                                \
+                *(.text.init.refok)
 
 /* sched.text is aling to function alignment to secure we have same
  * address even at second ld pass when generating System.map */
diff --git a/include/linux/init.h b/include/linux/init.h
index e007ae4dc41e..56ec4c62eee0 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -45,6 +45,19 @@
 #define __exitdata      __attribute__ ((__section__(".exit.data")))
 #define __exit_call     __attribute_used__ __attribute__ ((__section__ (".exitcall.exit")))
 
+/* modpost check for section mismatches during the kernel build.
+ * A section mismatch happens when there are references from a
+ * code or data section to an init section (both code or data).
+ * The init sections are (for most archs) discarded by the kernel
+ * when early init has completed so all such references are potential bugs.
+ * For exit sections the same issue exists.
+ * The following markers are used for the cases where the reference to
+ * the init/exit section (code or data) is valid and will teach modpost
+ * not to issue a warning.
+ * The markers follow same syntax rules as __init / __initdata. */
+#define __init_refok     noinline __attribute__ ((__section__ (".text.init.refok")))
+#define __initdata_refok          __attribute__ ((__section__ (".data.init.refok")))
+
 #ifdef MODULE
 #define __exit          __attribute__ ((__section__(".exit.text")))
 #else