linux-kernel - Re: [PATCH 03/11] x86: fix math

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Message-ID: <73c1f2160902090913n20283872r2cb5ae774560d047@mail.gmail.com>
Date:	Mon, 9 Feb 2009 12:13:33 -0500
From:	Brian Gerst <brgerst@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	hpa@...or.com, jeremy@...p.org, tglx@...utronix.de, mingo@...e.hu,
	linux-kernel@...r.kernel.org, x86@...nel.org, rusty@...tcorp.com.au
Subject: Re: [PATCH 03/11] x86: fix math_emu register frame access

On Mon, Feb 9, 2009 at 8:39 AM, Tejun Heo <tj@...nel.org> wrote:
> do_device_not_available() is the handler for #NM and it declares that
> it takes a unsigned long and calls math_emu(), which takes a long
> argument and surprisingly expects the stack frame starting at the zero
> argument would match struct math_emu_info, which isn't true regardless
> of configuration in the current code.
>
> This patch makes do_device_not_available() take struct pt_regs like
> other exception handlers and initialize struct math_emu_info with
> pointer to it and pass pointer to the math_emu_info to math_emulate()
> like normal C functions do.  This way, unless gcc makes a copy of
> struct pt_regs in do_device_not_available(), the register frame is
> correctly accessed regardless of kernel configuration or compiler
> used.
>
> This doesn't fix all math_emu problems but it at least gets it
> somewhat working.
>
> Signed-off-by: Tejun Heo <tj@...nel.org>
>
> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index afb46c0..84bdf8f 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -900,7 +900,7 @@ asmlinkage void math_state_restore(void)
>  EXPORT_SYMBOL_GPL(math_state_restore);
>
>  #ifndef CONFIG_MATH_EMULATION
> -asmlinkage void math_emulate(long arg)
> +void math_emulate(struct math_emu_info *info)

You forgot to drop the asmlinkage from the prototype in traps.h.

>  {
>        printk(KERN_EMERG
>                "math-emulation not enabled and no coprocessor found.\n");
> @@ -910,16 +910,19 @@ asmlinkage void math_emulate(long arg)
>  }
>  #endif /* CONFIG_MATH_EMULATION */
>
> -dotraplinkage void __kprobes
> -do_device_not_available(struct pt_regs *regs, long error)
> +dotraplinkage void __kprobes do_device_not_available(struct pt_regs regs)

Why did you change this to pass by value?  This is called from the
generic trap handler (error_code), which already passes the pt_regs
pointer in %eax.

--
Brian Gerst
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