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@xxxxxxxxxxxxxxx>
---
include/linux/init.h | 20 +++++++++++++++++++-
1 file changed, 19 insertions(+), 1 deletion(-)
diff --git a/include/linux/init.h b/include/linux/init.h
index e168880..a3ba270 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.
--
1.8.5.2
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