Messages in this thread | | | Date | Mon, 20 Aug 2012 12:00:44 +0100 | From | "Jan Beulich" <> | Subject | Re: [PATCH 55/74] lto, workaround: Add workaround for initcall reordering |
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>>> On 19.08.12 at 17:01, Andi Kleen <andi@firstfloor.org> wrote: > On Sun, Aug 19, 2012 at 09:46:04AM +0100, Jan Beulich wrote: >> >>> Andi Kleen <andi@firstfloor.org> 08/19/12 5:05 AM >>> >> >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 is not even true on x86, not to speak of generally. > > Why is it not true ? > > __initcall is only defined for !MODULE and there __exit discards.
__exit, on x86 and perhaps other arches, causes the code to be discarded at runtime only.
>> >+#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) \ >> >> Why not put it into e.g. section .discard.text? That could be expected to be >> discarded by the linker without being arch dependent, as long as all arches >> use DISCARDS in their linker script. > > > That's what __exit does, doesn't it?
No - see above. Using .discard.* enforces the discarding at link time.
Jan
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