linux-kernel - Re: [PATCH, RFC] x86: also CFI-annotate certain inline asm()s

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Date:	Mon, 10 Nov 2014 11:01:17 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Jan Beulich <JBeulich@...e.com>
Cc:	mingo@...e.hu, tglx@...utronix.de, hpa@...or.com,
	Tony Jones <tonyj@...e.de>, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH, RFC] x86: also CFI-annotate certain inline asm()s


* Jan Beulich <JBeulich@...e.com> wrote:

> @@ -11,6 +14,7 @@
>  static inline unsigned long native_save_fl(void)
>  {
>  	unsigned long flags;
> +	CFI_DECL;
>  
>  	/*
>  	 * "=rm" is safe here, because "pop" adjusts the stack before
> @@ -18,9 +22,10 @@ static inline unsigned long native_save_
>  	 * documented behavior of the "pop" instruction.
>  	 */
>  	asm volatile("# __raw_save_flags\n\t"
> -		     "pushf ; pop %0"
> +		     "pushf" CFI_ADJUST_CFA_OFFSET(1) "\n\t"
> +		     "pop %0" CFI_ADJUST_CFA_OFFSET(-1)
>  		     : "=rm" (flags)
> -		     : /* no input */
> +		     : CFI_INPUTS()
>  		     : "memory");
>  
>  	return flags;
> @@ -28,10 +33,13 @@ static inline unsigned long native_save_
>  
>  static inline void native_restore_fl(unsigned long flags)
>  {
> -	asm volatile("push %0 ; popf"
> +	CFI_DECL;
> +
> +	asm volatile("push %[flags]" CFI_ADJUST_CFA_OFFSET(1) "\n\t"
> +		     "popf" CFI_ADJUST_CFA_OFFSET(-1)
>  		     : /* no output */
> -		     :"g" (flags)
> -		     :"memory", "cc");
> +		     : CFI_INPUTS([flags] "g" (flags))
> +		     : "memory", "cc");
>  }

In principle I'm not against generating better debug info for our 
assembly code, but I think it should be more readable - for 
example I would not hide 'cfi_var' in the CFI_DECL above but I'd 
make it something like:

	CFI_DECL(cfi_var);

	...
		CFI_ADJUST_CFA_OFFSET(cfi_var, ...);

etc. - even if this is slightly more verbose than what you wrote.

There's few things worse than hidden state connections between 
various primitives - even if this is build only.

I'd also suggest splitting up the patch into 'add new primitives' 
and 'use them to improve stuff' parts.

(Assuming nobody objects strongly.)

Thanks,

	Ingo
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