linux-kernel - Re: [PATCH x86/mm] x86_64 save_i387

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Message-Id: <20080111213147.EBE0C26F9A9@magilla.localdomain>
Date:	Fri, 11 Jan 2008 13:31:47 -0800 (PST)
From:	Roland McGrath <roland@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH x86/mm] x86_64 save_i387_ia32 snafu

> thanks, applied. Does this explain the crash/hang problems with 32-bit 
> apps on 64-bit kernels? What was the exact failure mode?

It does.  Any 32-bit process trying to run a signal handler when it had
used the FPU, would clobber "current" with FP bits.  The observed failure
mode was shortly after this in the signal handler setup code, when it
crashed due to current->mm being zero (current->pid also being zero, and
the whole first 512 bytes of the task_struct being garbage).

Thanks,
Roland
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