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Subject[PATCH 55/74] lto, workaround: Add workaround for initcall reordering
Date
From: Andi Kleen <ak@linux.intel.com>

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 Honza Hubicka for suggesting this technique.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
include/linux/init.h | 20 +++++++++++++++++++-
1 files changed, 19 insertions(+), 1 deletions(-)
diff --git a/include/linux/init.h b/include/linux/init.h
index c2f06b3..e425800 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -176,6 +176,23 @@ 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.
@@ -188,7 +205,8 @@ extern bool initcall_debug;

#define __define_initcall(level,fn,id) \
static initcall_t __initcall_##fn##id __used \
- __attribute__((__section__(".initcall" level ".init"))) = fn
+ __attribute__((__section__(".initcall" level ".init"))) = fn \
+ LTO_REFERENCE_INITCALL(__initcall_##fn##id)

/*
* Early initcalls run before initializing SMP.
--
1.7.7.6


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