On Thu, 2015-03-26 at 13:40 +0100, Mason wrote:
> 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...
True. It's probably not feasible though.
Tracking string deduplication/reuse would be pretty difficult.
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