Re: [PATCH] x86: avoid warning for zero-filling .bss

From: Josh Poimboeuf
Date: Thu Nov 17 2016 - 16:02:55 EST


On Wed, Nov 16, 2016 at 03:17:09PM +0100, Arnd Bergmann wrote:
> The latest binutils are warning about a .fill directive with an explicit
> value in a .bss section:
>
> arch/x86/kernel/head_32.S: Assembler messages:
> arch/x86/kernel/head_32.S:677: Warning: ignoring fill value in section `.bss..page_aligned'
> arch/x86/kernel/head_32.S:679: Warning: ignoring fill value in section `.bss..page_aligned'
>
> This comes from the 'ENTRY()' macro padding the space between the symbols
> with 'nop'. Open-coding the .globl directive without the padding
> avoids that warning.

How is there space between the symbols? Aren't they already aligned?

Isn't the warning really about the fact that it's unnecessarily filling
a .bss section with zeros? Would it make sense to use .align instead?

> ---
> arch/x86/kernel/head_32.S | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
> index df541ac2071e..4e8577d03372 100644
> --- a/arch/x86/kernel/head_32.S
> +++ b/arch/x86/kernel/head_32.S
> @@ -669,14 +669,17 @@ __PAGE_ALIGNED_BSS
> initial_pg_pmd:
> .fill 1024*KPMDS,4,0
> #else
> -ENTRY(initial_page_table)
> +.globl initial_page_table
> +initial_page_table:
> .fill 1024,4,0
> #endif
> initial_pg_fixmap:
> .fill 1024,4,0
> -ENTRY(empty_zero_page)
> +.globl empty_zero_page
> +empty_zero_page:
> .fill 4096,1,0
> -ENTRY(swapper_pg_dir)
> +.globl swapper_pg_dir
> +swapper_pg_dir:
> .fill 1024,4,0
> EXPORT_SYMBOL(empty_zero_page)
>
> --
> 2.9.0
>

--
Josh