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authorAndi Kleen <ak@linux.intel.com>2014-02-08 09:01:08 +0100
committerH. Peter Anvin <hpa@linux.intel.com>2014-02-13 20:24:13 -0800
commitef1b893c29d0dba778f67ad97b554b37f9108dcc (patch)
treec77e509d240979f0718d6778a6abfe42fc0b59c3
parent128ea04a9885af9629059e631ddf0cab4815b589 (diff)
downloadlinux-ef1b893c29d0dba778f67ad97b554b37f9108dcc.tar.bz2
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: 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>
-rw-r--r--include/linux/init.h20
1 files changed, 19 insertions, 1 deletions
diff --git a/include/linux/init.h b/include/linux/init.h
index e1688802964f..a3ba27076342 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -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.