linux-kernel - Re: [PATCH] Make alignment cflags configurable.

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Message-ID: <C8B88EE3-7B49-4E59-BC7E-EB0A58FD7CF4@zytor.com>
Date:	Wed, 12 Aug 2015 15:37:05 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jan-Simon Moeller <dl9pf@....de>,
	David Woodhouse <dwmw2@...radead.org>
CC:	tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
	linux-kernel@...r.kernel.org, llvmlinux@...ts.linuxfoundation.org,
	behanw@...verseincode.com
Subject: Re: [PATCH] Make alignment cflags configurable.

NAK.  This is crazy.

On August 12, 2015 3:30:19 PM PDT, Jan-Simon Moeller <dl9pf@....de> wrote:
>Hi all!
>
>> You could mention that this is to fix the clang build. But why is it
>> needed? It isn't that clang just doesn't accept the option, is it?
>> Otherwise we could just use $(call cc-option, -falign-jumps=1) etc.
>
>Yes it is to fix the build with clang. 
>I tried cc-option, but it does not improve the situation (more below).
>This is  why I chose the config option approach in the patch.
>
> 
>> Did you get to the bottom of the clang failure here? Just turning
>this
>> off without a coherent explanation doesn't seem like the right thing
>to
>> do.
>
>I know it is not the final solution which is why I turned it into a
>config 
>option. We can still debate if default should be "y" or "n". This way
>we all 
>can proceed.
>
>@Ingo: would it be fine if we wrap it into a config option defaulting
>to "y" ?
>
>
>What I can say so far is that although clang warns about the unknown
>option
>and ignores it, the resulting kernel still fails to boot somewhere
>early in 
>start_kernel(). I'm still investigating. 
>
>My current trace ends like this:
>page_address_init ~ setup_arch ~ then arch/x86/kernel/setup.c:898
>setup.c:898 is a printk actually ... 
>early_idt_handler_array[i]  ~> early_idt_handler_common
>
>The mail thread is here:
>http://lists.linuxfoundation.org/pipermail/llvmlinux/2015-August/001276.html
>
>
><wild guess>
>We still build with -no-integrated-as which means we use gas. Maybe the
>flag
>is passed-on there and things get confused. 
></wile guess>
>
>Best,
>Jan-Simon

-- 
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