linux-kernel - Re: [PATCH] Bring sparc64 dynamic ftrace up to snuff...

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Message-ID: <20090613194027.GA25439@elte.hu>
Date:	Sat, 13 Jun 2009 21:40:27 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	David Miller <davem@...emloft.net>
Cc:	linux-kernel@...r.kernel.org, sparclinux@...r.kernel.org,
	rostedt@...dmis.org
Subject: Re: [PATCH] Bring sparc64 dynamic ftrace up to snuff...


* David Miller <davem@...emloft.net> wrote:

>  int ftrace_update_ftrace_func(ftrace_func_t func)
>  {
>  	unsigned long ip = (unsigned long)(&ftrace_call);
> -	unsigned char old[MCOUNT_INSN_SIZE], *new;
> +	u32 old, new;
>  
> -	memcpy(old, &ftrace_call, MCOUNT_INSN_SIZE);
> +	old = *(u32 *) &ftrace_call;

btw., just one (really stupid) question here: can ftrace_call be 
misaligned, and is misalignment a problem on Sparc? If it's not a 
problem then disregard the rest of the mail.

I dont see a particular alignment done in mcount.S:

ftrace_caller:
        mov             %i7, %o1
        mov             %o7, %o0
        .globl          ftrace_call
ftrace_call:
        call            ftrace_stub

so replacing an memcpy (which can copy misaligned buffers) with a 
direct assignment (which cannot) - wont that cause misalignment on 
Sparc?

	Ingo
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