[PATCH] Extract initrd free logic from arch-specific code.

[Geert Uytterhoeven]

On Thu, Mar 29, 2018 at 5:27 PM, Russell King - ARM Linux
<linux at armlinux.org.uk> wrote:
> On Thu, Mar 29, 2018 at 09:37:52AM +1100, Oliver wrote:
>> On Thu, Mar 29, 2018 at 9:14 AM, Russell King - ARM Linux
>> <linux at armlinux.org.uk> wrote:
>> > On Wed, Mar 28, 2018 at 02:04:22PM -0500, Rob Landley wrote:
>> >> On 03/28/2018 11:48 AM, Russell King - ARM Linux wrote:
>> >> > On Wed, Mar 28, 2018 at 10:58:51AM -0500, Rob Landley wrote:
>> >> >> On 03/28/2018 10:26 AM, Shea Levy wrote:
>> >> >>> Now only those architectures that have custom initrd free requirements
>> >> >>> need to define free_initrd_mem.
>> >> >> ...
>> >> >>> --- a/arch/arc/mm/init.c
>> >> >>> +++ b/arch/arc/mm/init.c
>> >> >>> @@ -229,10 +229,3 @@ void __ref free_initmem(void)
>> >> >>>  {
>> >> >>>   free_initmem_default(-1);
>> >> >>>  }
>> >> >>> -
>> >> >>> -#ifdef CONFIG_BLK_DEV_INITRD
>> >> >>> -void __init free_initrd_mem(unsigned long start, unsigned long end)
>> >> >>> -{
>> >> >>> - free_reserved_area((void *)start, (void *)end, -1, "initrd");
>> >> >>> -}
>> >> >>> -#endif
>> >> >>> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
>> >> >>> index 3f972e83909b..19d1c5594e2d 100644
>> >> >>> --- a/arch/arm/Kconfig
>> >> >>> +++ b/arch/arm/Kconfig
>> >> >>> @@ -47,6 +47,7 @@ config ARM
>> >> >>>   select HARDIRQS_SW_RESEND
>> >> >>>   select HAVE_ARCH_AUDITSYSCALL if (AEABI && !OABI_COMPAT)
>> >> >>>   select HAVE_ARCH_BITREVERSE if (CPU_32v7M || CPU_32v7) && !CPU_32v6
>> >> >>> + select HAVE_ARCH_FREE_INITRD_MEM
>> >> >>>   select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL && !CPU_ENDIAN_BE32 && MMU
>> >> >>>   select HAVE_ARCH_KGDB if !CPU_ENDIAN_BE32 && MMU
>> >> >>>   select HAVE_ARCH_MMAP_RND_BITS if MMU
>> >> >>
>> >> >> Isn't this why weak symbols were invented?
>> >> >
>> >> > Weak symbols means that we end up with both the weakly-referenced code
>> >> > and the arch code in the kernel image.  That's fine if the weak code
>> >> > is small.
>> >>
>> >> The kernel's been able to build with link time garbage collection since 2016:
>> >>
>> >> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b67067f1176d
>> >>
>> >> Wouldn't that remove the unused one?
>> >
>> > Probably, if anyone bothered to use that, which they don't.
>> >
>> > LD_DEAD_CODE_DATA_ELIMINATION is a symbol without a prompt, and from
>> > what I can see, nothing selects it.  Therefore, the symbol is always
>> > disabled, and so the feature never gets used in mainline kernels.
>> >
>> > Brings up the obvious question - why is it there if it's completely
>> > unused?  (Maybe to cause confusion, and allowing a justification
>> > for __weak ?)
>>
>> IIRC Nick had some patches to do the arch enablement for powerpc, but
>> I'm not sure what happened to them though. I suspect it just fell down
>> Nick's ever growing TODO list.
>
> I've given it a go on ARM, marking every linker-built table with KEEP()
> and comparing the System.map files.  The resulting kernel is around
> 150k smaller, which seems good.
>
> However, it doesn't boot - and I don't know why.  Booting the kernel
> under kvmtool in a VM using virtio-console, I can find no way to get
> any kernel messages out of it.  Using lkvm debug, I can see that the
> PC is stuck inside die(), and that's the only information I have.
> It dies before bringing up the other CPUs, so it's a very early death.
>
> I don't think other console types are available under ARM64.

earlycon?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds