Date: Mon, 25 Aug 1997 19:08:24 -0700 (PDT) From: mef@cs.washington.edu To: bde@zeta.org.au Cc: smp@FreeBSD.ORG, ulbright@cs.washington.edu Subject: Re: write protection settings Message-ID: <199708260208.TAA05721@porky-pig.cs.washington.edu> In-Reply-To: <199708252250.IAA00439@godzilla.zeta.org.au> (message from Bruce Evans on Tue, 26 Aug 1997 08:50:35 %2B1000)
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Date: Tue, 26 Aug 1997 08:50:35 +1000 From: Bruce Evans <bde@zeta.org.au> >Can someone tell me where write protection bits are set for the kernel >text? In locore.s. Found it and just needed to add a little ifdef to do the map_read_write stuff. Got our ttd debugger to set breakpoints. >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. We had the 4MB page handling stuff turned off (for reasons specific to our setup). Thanks for responding so quickly. Marc
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