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Date: Fri, 13 Feb 2009 02:36:41 +0100
From: Olivier Houchard <mlfbsd@ci0.org>
To: Mark Tinguely <tinguely@casselton.net>
Message-ID: <20090213013641.GA41307@ci0.org>
References: <200902122201.n1CM1wbK018744@casselton.net>
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Cc: freebsd-arm@freebsd.org
Subject: Re: thread0.td_frame overwritten in cpu_startup()
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On Thu, Feb 12, 2009 at 04:01:58PM -0600, Mark Tinguely wrote:
> 
> on startup, the initarm() sets the thread0.td_frame to a local trapframe
> structure.
> 
> in arm/ARCH/ARCH_machdep.c
> 	thread0.td_frame = &proc0_tf;
> 
> But cpu_startup() in arm/arm/machdep.c overwrites it with a value at the end
> of the kernel stack. unfortunately, that space is also used by the thread0
> pcb structure.
> 
> in arm/ARCH/ARCH_machdep.c
> 	thread0.td_pcb = (struct pcb *)
> 		(thread0.td_kstack + KSTACK_PAGES * PAGE_SIZE) - 1
> 
> in arm/arm/machdep.c
> 	pcb->un_32.pcb32_sp = (u_int)thread0.td_kstack +
> 	   USPACE_SVC_STACK_TOP;
> 
> note: USPACE_SVC_STACK_TOP is defined as KSTACK_PAGES * PAGE_SIZE, so this
> is the top of the kernel stack. 
> 
> 	thread0.td_frame = (struct trapframe *)pcb->un_32.pcb32_sp - 1;
> 
> This td_frame assignment in arm/arm/machdep.c should be removed. Not only
> did it overwrite a perfectly good trapframe, it overwrited it with memory
> that is shared with the pcb.
> 

True, committed.

Thanks !

Olivier