param: make sure charp isn't used as a core_param

"charp" sets a variable to point to a char string in a command line.
This doesn't work if the command line isn't going to stick around.
Add a compile-breaking check for this case, and make a note of it.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
---
 include/linux/moduleparam.h |   16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -118,11 +118,15 @@ struct kparam_array
  * early in boot.  This is for compatibility with __setup(), and it
  * makes sense as truly core parameters aren't tied to the particular
  * file they're in.
+ *
+ * Note: You can't use 'charp' here (which keeps a pointer into our
+ * tmp cmdline).
  */
 #define core_param(name, var, type, perm)				\
 	param_check_##type(name, &(var));				\
 	__module_param_call("", "__core_param", name, param_set_##type, \
-			    param_get_##type, &var, perm)
+			    param_get_##type, &var, perm		\
+			    + BUILD_BUG_ON_ZERO(param_##type##_keeps_reference))
 #endif /* !MODULE */
 
 /* Actually copy string: maxlen param is usually sizeof(string). */
@@ -150,42 +154,52 @@ extern int param_set_byte(const char *va
 extern int param_set_byte(const char *val, struct kernel_param *kp);
 extern int param_get_byte(char *buffer, struct kernel_param *kp);
 #define param_check_byte(name, p) __param_check(name, p, unsigned char)
+#define param_byte_keeps_reference 0
 
 extern int param_set_short(const char *val, struct kernel_param *kp);
 extern int param_get_short(char *buffer, struct kernel_param *kp);
 #define param_check_short(name, p) __param_check(name, p, short)
+#define param_short_keeps_reference 0
 
 extern int param_set_ushort(const char *val, struct kernel_param *kp);
 extern int param_get_ushort(char *buffer, struct kernel_param *kp);
 #define param_check_ushort(name, p) __param_check(name, p, unsigned short)
+#define param_ushort_keeps_reference 0
 
 extern int param_set_int(const char *val, struct kernel_param *kp);
 extern int param_get_int(char *buffer, struct kernel_param *kp);
 #define param_check_int(name, p) __param_check(name, p, int)
+#define param_int_keeps_reference 0
 
 extern int param_set_uint(const char *val, struct kernel_param *kp);
 extern int param_get_uint(char *buffer, struct kernel_param *kp);
 #define param_check_uint(name, p) __param_check(name, p, unsigned int)
+#define param_uint_keeps_reference 0
 
 extern int param_set_long(const char *val, struct kernel_param *kp);
 extern int param_get_long(char *buffer, struct kernel_param *kp);
 #define param_check_long(name, p) __param_check(name, p, long)
+#define param_long_keeps_reference 0
 
 extern int param_set_ulong(const char *val, struct kernel_param *kp);
 extern int param_get_ulong(char *buffer, struct kernel_param *kp);
 #define param_check_ulong(name, p) __param_check(name, p, unsigned long)
+#define param_ulong_keeps_reference 0
 
 extern int param_set_charp(const char *val, struct kernel_param *kp);
 extern int param_get_charp(char *buffer, struct kernel_param *kp);
 #define param_check_charp(name, p) __param_check(name, p, char *)
+#define param_charp_keeps_reference 1
 
 extern int param_set_bool(const char *val, struct kernel_param *kp);
 extern int param_get_bool(char *buffer, struct kernel_param *kp);
 #define param_check_bool(name, p) __param_check(name, p, int)
+#define param_bool_keeps_reference 0
 
 extern int param_set_invbool(const char *val, struct kernel_param *kp);
 extern int param_get_invbool(char *buffer, struct kernel_param *kp);
 #define param_check_invbool(name, p) __param_check(name, p, int)
+#define param_invbool_keeps_reference 0
 
 /* Comma-separated array: *nump is set to number they actually specified. */
 #define module_param_array_named(name, array, type, nump, perm)		\