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Date: Tue, 26 Aug 1997 08:50:35 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199708252250.IAA00439@godzilla.zeta.org.au>
To: smp@FreeBSD.ORG, ulbright@cs.washington.edu
Subject: Re: write protection settings
Sender: owner-freebsd-smp@FreeBSD.ORG
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>Can someone tell me where write protection bits are set for the kernel
>text?  

In locore.s.

>I'm experiencing a pagefault when setting a breakpoint in my
>debugger and it seems to occur when writing to the memory address where
>the bp is to go.

That bug was normal for a month or two until a few weeks ago.  The bug
was in 4MB page handling (which I think isn't used for SMP).  The
kernel text is normally entirely unprotected when 4MB pages are used
(this is another bug; 4MB data section alignment is required to fix it)
but ddb attempts to unprotect the text on the fly anyway, and it used
to write to wong places in the page tables when the relevant text
address is in a 4MB page.

Bruce