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Commit ef1b893c authored by Andi Kleen's avatar Andi Kleen Committed by H. Peter Anvin
Browse files

lto, workaround: Add workaround for initcall reordering 



Work around a LTO gcc problem: when there is no reference to a variable
in a module it will be moved to the end of the program. This causes
reordering of initcalls which the kernel does not like.
Add a dummy reference function to avoid this. The function is
deleted by the linker.

This replaces a previous much slower workaround.

Thanks to Jan "Honza" Hubička for suggesting this technique.

Suggested-by: default avatarJan Hubička <hubicka@ucw.cz>
Signed-off-by: default avatarAndi Kleen <ak@linux.intel.com>
Link: http://lkml.kernel.org/r/1391846481-31491-4-git-send-email-ak@linux.intel.com


Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
parent 128ea04a

include/linux/init.h

+19 −1
Original line number Diff line number Diff line
@@ -163,6 +163,23 @@ extern bool initcall_debug; 


#ifndef __ASSEMBLY__



#ifdef CONFIG_LTO

/* Work around a LTO gcc problem: when there is no reference to a variable

 * in a module it will be moved to the end of the program. This causes

 * reordering of initcalls which the kernel does not like.

 * Add a dummy reference function to avoid this. The function is

 * deleted by the linker.

 */

#define LTO_REFERENCE_INITCALL(x) \

	; /* yes this is needed */			\

	static __used __exit void *reference_##x(void)	\

	{						\

		return &x;				\

	}

#else

#define LTO_REFERENCE_INITCALL(x)

#endif



/* initcalls are now grouped by functionality into separate 

 * subsections. Ordering inside the subsections is determined

 * by link order.
@@ -175,7 +192,8 @@ extern bool initcall_debug; 


#define __define_initcall(fn, id) \

	static initcall_t __initcall_##fn##id __used \

	__attribute__((__section__(".initcall" #id ".init"))) = fn

	__attribute__((__section__(".initcall" #id ".init"))) = fn; \

	LTO_REFERENCE_INITCALL(__initcall_##fn##id)



/*

 * Early initcalls run before initializing SMP.