linux-kernel - Re: [PATCH v3 1/4] kbuild: Don't define ALIGN and ENTRY when preprocessing linker scripts.

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Date:	Sun, 20 Sep 2009 23:16:27 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Tim Abbott <tabbott@...lice.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/4] kbuild: Don't define ALIGN and ENTRY when
	preprocessing linker scripts.

On Sun, Sep 20, 2009 at 02:43:10PM -0400, Tim Abbott wrote:
> Adding a reference to <linux/linkage.h> to x86's <asm/cache.h> causes
> the x86 linker script to have syntax errors, because the ALIGN and
> ENTRY keywords get redefined to the assembly implementations of those.
> One could fix this by adjusting the include structure, but I think any
> solution based on that approach would be fragile.
> 
> Currently, it is impossible when writing a header to do something
> different for assembly files and linker scripts, even though there are
> clearly cases where one wants them to define macros differently for
> the two (ENTRY being an excellent example).  So I think the right
> solution here is to introduce a new preprocessor definition,
> tentatively called __LINKER_SCRIPT__ that is set along with
> __ASSEMBLY__ for linker scripts, and to use that to not define ALIGN
> and ENTRY in linker scripts.  I suspect we'll find other uses for this
> mechanism in the future.

We will need this - agreed.

The reason for __XXX___ for ASSEMBLY and KERNEL is the fact
that these are used in user space headers.

I would suggest to use: LINKER_SCRIPT

> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 5c4b7a4..e51e213 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -269,7 +269,8 @@ targets += $(extra-y) $(MAKECMDGOALS) $(always)
>  # Linker scripts preprocessor (.lds.S -> .lds)
>  # ---------------------------------------------------------------------------
>  quiet_cmd_cpp_lds_S = LDS     $@
> -      cmd_cpp_lds_S = $(CPP) $(cpp_flags) -D__ASSEMBLY__ -o $@ $<
> +      cmd_cpp_lds_S = $(CPP) $(cpp_flags) -D__ASSEMBLY__ -D__LINKER_SCRIPT__ \
> +		      -o $@ $<

This will conflict (in a trivial way) with stuff I have
pending for this merge window.

	Sam
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