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Commit 0e0d314e authored by Sam Ravnborg's avatar Sam Ravnborg
Browse files

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: default avatarSam Ravnborg <sam@ravnborg.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
parent ca967258

include/asm-generic/vmlinux.lds.h

+4 −2
Original line number Diff line number Diff line
@@ -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 */

include/linux/init.h

+13 −0
Original line number Diff line number Diff line
@@ -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

scripts/mod/modpost.c

+11 −0
Original line number Diff line number Diff line
@@ -583,6 +583,12 @@ static int strrcmp(const char *s, const char *sub) 


/**

 * Whitelist to allow certain references to pass with no warning.

 *

 * Pattern 0:

 *   Do not warn if funtion/data are marked with __init_refok/__initdata_refok.

 *   The pattern is identified by:

 *   fromsec = .text.init.refok | .data.init.refok

 *

 * Pattern 1:

 *   If a module parameter is declared __initdata and permissions=0

 *   then this is legal despite the warning generated.
@@ -686,6 +692,11 @@ static int secref_whitelist(const char *modname, const char *tosec, 
		NULL

	};



	/* Check for pattern 0 */

	if ((strcmp(fromsec, ".text.init.refok") == 0) ||

	    (strcmp(fromsec, ".data.init.refok") == 0))

		return 1;



	/* Check for pattern 1 */

	if (strcmp(tosec, ".init.data") != 0)

		f1 = 0;