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

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On Thu, Nov 17, 2016 at 11:32:30PM +0100, Arnd Bergmann wrote:
> On Thursday, November 17, 2016 3:02:48 PM CET Josh Poimboeuf wrote:
> > 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?
> 
> My understanding is that they are aligned, it's just that gas complains
> about the .align directive with a nonzero fill value.

Ah, I see now.  In that case your patch looks fine to me.

Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>

> 
> > 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?
> 
> Filling with zeroes is allowed, and that's what we are intending anyway.
> .align would not do the right thing here as it only adds padding if it's
> not already aligned, but we know it is.

-- 
Josh

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[PATCH] x86: avoid warning for zero-filling .bss Arnd Bergmann <arnd@arndb.de> - 2016-11-16 15:20 +0100
  [tip:x86/urgent] x86/boot: Avoid warning for zero-filling .bss tip-bot for Arnd Bergmann <tipbot@zytor.com> - 2016-11-17 08:30 +0100
  Re: [PATCH] x86: avoid warning for zero-filling .bss Josh Poimboeuf <jpoimboe@redhat.com> - 2016-11-17 22:10 +0100
    Re: [PATCH] x86: avoid warning for zero-filling .bss hpa@zytor.com - 2016-11-17 22:20 +0100
    Re: [PATCH] x86: avoid warning for zero-filling .bss Arnd Bergmann <arnd@arndb.de> - 2016-11-17 23:40 +0100
      Re: [PATCH] x86: avoid warning for zero-filling .bss Josh Poimboeuf <jpoimboe@redhat.com> - 2016-11-17 23:50 +0100
        Re: [PATCH] x86: avoid warning for zero-filling .bss "H. Peter Anvin" <hpa@zytor.com> - 2016-11-18 01:10 +0100

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