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 <XyZc>: $ 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 <XyZc>: c020d928 <XyZc>: 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 <printk> c020d940: e3000090 movw r0, #144 ; 0x90 c020d944: e34c0022 movt r0, #49186 ; 0xc022 c020d948: ebfe00c6 bl c018dc68 <printk> 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
