linux-kernel - Re: Warning from ring buffer code (Was: Re: linux-next: tip tree build warning)

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Message-ID: <70318cbf0909141009v46581785m4c70edf31fcb79fa@mail.gmail.com>
Date:	Mon, 14 Sep 2009 10:09:27 -0700
From:	Christopher Li <sparse@...isli.org>
To:	Steven Rostedt <srostedt@...hat.com>
Cc:	Jaswinder Singh Rajput <jaswinder@...nel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-sparse@...r.kernel.org, Josh Triplett <josh@...edesktop.org>
Subject: Re: Warning from ring buffer code (Was: Re: linux-next: tip tree 
	build warning)

On Mon, Sep 14, 2009 at 8:16 AM, Steven Rostedt <srostedt@...hat.com> wrote:
> static void func(int size_me) {
>        char array[size_me];
>
>        memcpy(array, "hello", size);
> };
>
> and sparse failed on it as well. Note, you need to have something call
> func, or sparse will ignore it.

Gcc allows variable size. Sparse expects the size of an array is constant.
For the kernel using variable array size is consider bad. Because the kernel
has very limited stack size. (8K if I remember correctly). Using dynamic array
is very easy to overflow the stack without realizing it.

It deserves a warning. I agree the warning message can use a better description
though.

Chris
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