linux-kernel - Re: [PATCH 2/2] x86: dumpstack: eliminate some #ifdefs

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Date:	Wed, 7 Oct 2015 09:03:21 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Jiri Slaby <jslaby@...e.cz>, Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Michal Marek <mmarek@...e.cz>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] x86: dumpstack: eliminate some #ifdefs


* Rasmus Villemoes <linux@...musvillemoes.dk> wrote:

> +	static const char build_flags[] = ""
> +		CHOOSE_EXPR(CONFIG_PREEMPT, " PREEMPT")
> +		CHOOSE_EXPR(CONFIG_SMP, " SMP")
> +		CHOOSE_EXPR(CONFIG_DEBUG_PAGEALLOC, " DEBUG_PAGEALLOC")
> +		CHOOSE_EXPR(CONFIG_KASAN, " KASAN");
> +
>  	printk(KERN_DEFAULT
> -	       "%s: %04lx [#%d] ", str, err & 0xffff, ++die_counter);
> -#ifdef CONFIG_PREEMPT
> -	printk("PREEMPT ");
> -#endif
> -#ifdef CONFIG_SMP
> -	printk("SMP ");
> -#endif
> -#ifdef CONFIG_DEBUG_PAGEALLOC
> -	printk("DEBUG_PAGEALLOC ");
> -#endif
> -#ifdef CONFIG_KASAN
> -	printk("KASAN");
> -#endif
> -	printk("\n");
> +	       "%s: %04lx [#%d]%s\n", str, err & 0xffff, ++die_counter,
> +	       build_flags);
> +
>  	if (notify_die(DIE_OOPS, str, regs, err,
>  			current->thread.trap_nr, SIGSEGV) == NOTIFY_STOP)
>  		return 1;

Looks cleaner than what we had before, but I have a naming nit: CHOOSE_EXPR() is 
not something I'd be able to remember, I'd have to look it up again all the time, 
because it does not have 'config' in its name, and because 'choose' is usually 
associated with different constructs.

So how about something more intuitive, like:

		COND_CONFIG(CONFIG_PREEMPT,		" PREEMPT")
		COND_CONFIG(CONFIG_SMP,			" SMP")
		COND_CONFIG(CONFIG_DEBUG_PAGEALLOC,	" DEBUG_PAGEALLOC")
		COND_CONFIG(CONFIG_KASAN,		" KASAN");

or:

		IF_CONFIG(CONFIG_PREEMPT,		" PREEMPT")
		IF_CONFIG(CONFIG_SMP,			" SMP")
		IF_CONFIG(CONFIG_DEBUG_PAGEALLOC,	" DEBUG_PAGEALLOC")
		IF_CONFIG(CONFIG_KASAN,			" KASAN");

?

Both names are still unused in the kernel repo.

Thanks,

	Ingo
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