linux-kernel - Re: [PATCH v2] cris: arch-v10: kgdb: Add volatile for static variable is_dyn

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Date:	Tue, 4 Aug 2015 17:01:22 +0200
From:	Hans-Peter Nilsson <hans-peter.nilsson@...s.com>
To:	xili_gchen_5257@...mail.com
CC:	starvik@...s.com, jespern@...s.com, linux-cris-kernel@...s.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] cris: arch-v10: kgdb: Add volatile for static variable
 is_dyn_brkp

> From: Chen Gang <xili_gchen_5257@...mail.com>
> Date: Fri, 10 Jul 2015 23:50:07 +0200

> Within one C file, current gcc can optimize the global static variables
> according to the C code, but it will skip assembly code -- it will pass
> them to gas directly.
> 
> if the static variable is used between C code and assembly code in one C
> file (e.g. is_dyn_brkp in kgdb.c), it needs volatile to let gcc know it
> should not be optimized, or it may cause issue.

In this case it's *mostly* a matter of taste but please avoid
using volatile as a hammer when there are other tools available.

> -static unsigned char is_dyn_brkp = 0;
> +static volatile unsigned char is_dyn_brkp;

Please instead use "__used", i.e.
+static unsigned char __used is_dyn_brkp = 0;

brgds, H-P
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