From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752623AbbCZMkX (ORCPT ); Thu, 26 Mar 2015 08:40:23 -0400 Received: from smtp2-g21.free.fr ([212.27.42.2]:55092 "EHLO smtp2-g21.free.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751533AbbCZMkW (ORCPT ); Thu, 26 Mar 2015 08:40:22 -0400 Message-ID: <5513FE2F.3040306@free.fr> Date: Thu, 26 Mar 2015 13:40:15 +0100 From: Mason User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:35.0) Gecko/20100101 Firefox/35.0 SeaMonkey/2.32.1 MIME-Version: 1.0 To: Joe Perches CC: Linux ARM , LKML , Ingo Molnar , Mathias Krause Subject: Re: String literals in __init functions References: <5512F6C6.1020304@free.fr> <1427306517.2717.0.camel@perches.com> In-Reply-To: <1427306517.2717.0.camel@perches.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 25/03/2015 19:01, Joe Perches wrote: > On Wed, 2015-03-25 at 18:56 +0100, Mason wrote: > >> AFAIU, functions only used at system init are tagged __init to have >> the linker store them in a separate .init.text section, so memory can >> be reclaimed once initialization is complete. Is that correct? >> >> The corresponding tag for data is __initdata (section .init.data) >> >> I started wondering if the string literals used in an __init functions >> were automatically marked __initdata. >> >> Looking at the objdump output, I see that the string literals are, >> in fact, stored in the .rodata section. I suppose that .rodata is NOT >> reclaimed after init? >> >> This way seems to work: >> >> static char XyZa[] __initdata = KERN_ALERT "foo"; >> static const char XyZb[] __initconst = KERN_ALERT "bar"; >> void __init XyZc(void) { printk(XyZa); printk(XyZb); } >> >> $ arm-linux-gnueabihf-objdump -xd arch/arm/mach-tangox/time.o | grep XyZ >> 00000000 l O .init.data 00000006 XyZa >> 00000000 l O .init.rodata 00000006 XyZb >> 00000000 g F .init.text 00000028 XyZc >> 00000000 : >> >> $ arm-linux-gnueabihf-objdump -xd vmlinux | grep XyZ >> c021e360 l O .init.data 00000006 XyZa >> c0220090 l O .init.data 00000006 XyZb >> c020d928 g F .init.text 00000028 XyZc >> c020d928 : >> >> c020d928 : >> c020d928: e1a0c00d mov ip, sp >> c020d92c: e92dd800 push {fp, ip, lr, pc} >> c020d930: e24cb004 sub fp, ip, #4 >> c020d934: e30e0360 movw r0, #58208 ; 0xe360 >> c020d938: e34c0021 movt r0, #49185 ; 0xc021 >> c020d93c: ebfe00c9 bl c018dc68 >> c020d940: e3000090 movw r0, #144 ; 0x90 >> c020d944: e34c0022 movt r0, #49186 ; 0xc022 >> c020d948: ebfe00c6 bl c018dc68 >> c020d94c: e89da800 ldm sp, {fp, sp, pc} >> >> Did I miss something in init.h? >> Or should it be done like above to reclaim string literals? > > No, you didn't miss anything. > > One proposal: > > https://lkml.org/lkml/2014/8/21/255 Thanks for the link! Here's the equivalent gmane link for my own reference: http://thread.gmane.org/gmane.linux.kernel/1771969 Basically, if I understand correctly, Ingo NAKed the patch, saying this should be done automatically by the toolchain. That would make for an interesting side-project... For the record, I wrote a trivial wrapper for my limited use-case. #define printk_init(format, ...) do { \ static char fmt[] __initdata = format; printk(fmt, ## __VA_ARGS__); \ } while(0) (I dislike the "statement-in-expression" extension, because vim thinks there's a syntax error, and flashes a bright red block.) https://gcc.gnu.org/onlinedocs/cpp/Variadic-Macros.html https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html Regards. From mboxrd@z Thu Jan 1 00:00:00 1970 From: slash.tmp@free.fr (Mason) Date: Thu, 26 Mar 2015 13:40:15 +0100 Subject: String literals in __init functions In-Reply-To: <1427306517.2717.0.camel@perches.com> References: <5512F6C6.1020304@free.fr> <1427306517.2717.0.camel@perches.com> Message-ID: <5513FE2F.3040306@free.fr> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 25/03/2015 19:01, Joe Perches wrote: > On Wed, 2015-03-25 at 18:56 +0100, Mason wrote: > >> AFAIU, functions only used at system init are tagged __init to have >> the linker store them in a separate .init.text section, so memory can >> be reclaimed once initialization is complete. Is that correct? >> >> The corresponding tag for data is __initdata (section .init.data) >> >> I started wondering if the string literals used in an __init functions >> were automatically marked __initdata. >> >> Looking at the objdump output, I see that the string literals are, >> in fact, stored in the .rodata section. I suppose that .rodata is NOT >> reclaimed after init? >> >> This way seems to work: >> >> static char XyZa[] __initdata = KERN_ALERT "foo"; >> static const char XyZb[] __initconst = KERN_ALERT "bar"; >> void __init XyZc(void) { printk(XyZa); printk(XyZb); } >> >> $ arm-linux-gnueabihf-objdump -xd arch/arm/mach-tangox/time.o | grep XyZ >> 00000000 l O .init.data 00000006 XyZa >> 00000000 l O .init.rodata 00000006 XyZb >> 00000000 g F .init.text 00000028 XyZc >> 00000000 : >> >> $ arm-linux-gnueabihf-objdump -xd vmlinux | grep XyZ >> c021e360 l O .init.data 00000006 XyZa >> c0220090 l O .init.data 00000006 XyZb >> c020d928 g F .init.text 00000028 XyZc >> c020d928 : >> >> c020d928 : >> c020d928: e1a0c00d mov ip, sp >> c020d92c: e92dd800 push {fp, ip, lr, pc} >> c020d930: e24cb004 sub fp, ip, #4 >> c020d934: e30e0360 movw r0, #58208 ; 0xe360 >> c020d938: e34c0021 movt r0, #49185 ; 0xc021 >> c020d93c: ebfe00c9 bl c018dc68 >> c020d940: e3000090 movw r0, #144 ; 0x90 >> c020d944: e34c0022 movt r0, #49186 ; 0xc022 >> c020d948: ebfe00c6 bl c018dc68 >> c020d94c: e89da800 ldm sp, {fp, sp, pc} >> >> Did I miss something in init.h? >> Or should it be done like above to reclaim string literals? > > No, you didn't miss anything. > > One proposal: > > https://lkml.org/lkml/2014/8/21/255 Thanks for the link! Here's the equivalent gmane link for my own reference: http://thread.gmane.org/gmane.linux.kernel/1771969 Basically, if I understand correctly, Ingo NAKed the patch, saying this should be done automatically by the toolchain. That would make for an interesting side-project... For the record, I wrote a trivial wrapper for my limited use-case. #define printk_init(format, ...) do { \ static char fmt[] __initdata = format; printk(fmt, ## __VA_ARGS__); \ } while(0) (I dislike the "statement-in-expression" extension, because vim thinks there's a syntax error, and flashes a bright red block.) https://gcc.gnu.org/onlinedocs/cpp/Variadic-Macros.html https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html Regards.