linux-kernel - Re: [PATCH] x86: pgtable_32.h - prototype and section mismatch fixes

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Message-ID: <20080414183156.GA15287@uranus.ravnborg.org>
Date:	Mon, 14 Apr 2008 20:31:56 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Jacek Luczak <difrost.kernel@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: pgtable_32.h - prototype and section mismatch fixes

> 
> GCC is ok, I mean it inlines paravirt_pagetable_setup_[start,done] even with
> CONFIG_OPTIMIZE_INLINING=y:
> $ objdump -t vmlinux.o | grep pagetable_setup_start
> 0000a418 g     F .init.text     000000a1 native_pagetable_setup_start
> 
> While running with CONFIG_DEBUG_SECTION_MISMTCH=y it does not inline
> paravirt_pagetable_setup_start (_done is OK):
> $ objdump -t vmlinux.o | grep pagetable_setup_start
> 00017100 l     F .text  0000000b paravirt_pagetable_setup_start
> 00009fb0 g     F .init.text     00000089 native_pagetable_setup_start
> 
> DEBUG_SECTION_MISMATCH probably generated mismatch with smpboot_setup_io_apic()
> (commit: 96c968742fa1e6d64f979464acf2fd90cdc117b3, already merged). I will check
> and if __init is really superfluous I will post delta patch to remove all those
> __init annotations.
> 
> Similar situation might be found with unlock_ExtINT_logic()
> (arch/x86/kernel/io_apic_32.c), which I annotated with __init in one of previous
> patches, but here, this function IMO shouldn't be marked inline.

Hi Jacek.

Please consider following code snippet:

static void __init foo() {}

static void __init bar() { foo(); }

static void __init baz() { bar(); }

Browsing this code it makes perfect sense that when baz()
is annotated __init bar and suddenly foo() has same annotation.

There is no point in removing the __init annotation of bar()
just becasue we happen to know it will be inlined by gcc.
Removing the __init anotation is actually wrong - because
the __init annotation has a two-fold purpose.
It is used to locate this function in a section that
is later discarded.
But it is also used to document that this function
is only used in the early init of this driver/what-ever.
So using this function in non-__init code is wrong.

Therefore I recommend to keep the __init annotation
also for the inline functions - assuming these functions
are supposed to be used only in the early init as the annotation
says they are.

	Sam
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