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

[Russell King - ARM Linux]

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 ?)

-- 
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