lto, workaround: Add workaround for initcall reordering (ef1b893c) · Commits · 戴 / test

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:

Jan Hubička <hubicka@ucw.cz> Signed-off-by:

Andi Kleen <ak@linux.intel.com> Link: http://lkml.kernel.org/r/1391846481-31491-4-git-send-email-ak@linux.intel.com Signed-off-by:

H. Peter Anvin <hpa@linux.intel.com>

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.

Admin message