Date: Wed, 10 Sep 1997 14:40:45 +1000 From: Bruce Evans <bde@zeta.org.au> To: bde@zeta.org.au, jlemon@americantv.com Cc: emulation@FreeBSD.ORG, hfwirth@ping.at Subject: Re: Doscmd, debugging with gdb Message-ID: <199709100440.OAA10269@godzilla.zeta.org.au>
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>> > > cat /proc/<pid>/map
>> > [.. snip ..]
>> > 0x8012000 0x8014000 0 2 rwx COW vnode
>> > 0x8014000 0x801c000 0 8 rwx default
>> > [.. snip ..]
>> > (gdb) set *0x8012000 = 0
>> > (gdb) set *0x8014000 = 0
>> > Error accessing memory address 0x8014000: Bad address.
>>
>> `w' apparently means write-protected here :-). All the r-x COW vnodes
>> are writable and all the rwx COW vnodes are non-writable.
>
>No, I don't think that's it; the write to the 'rwx COW vnode' entry
>succeeds, while the write to the 'rwx default' entry fails.
Oops, I read from the wrong column in the map.
>Also, the 'default' region in doscmd was allocated via brk(), so I'd
>certainly hope that allocated memory isn't non-writeable. :-)
>
>I neglected to mention that this was on a -current machine, BTW.
Even the stack is currently non-writable via ptrace :-).
Try this fix.
diff -c2 vm_map.c~ vm_map.c
*** vm_map.c~ Mon Sep 1 18:00:38 1997
--- vm_map.c Wed Sep 10 14:02:48 1997
***************
*** 2288,2292 ****
(entry->eflags & MAP_ENTRY_COW) == 0 ||
(entry->wired_count != 0)) {
! if ((fault_type & (prot)) != fault_type)
RETURN(KERN_PROTECTION_FAILURE);
}
--- 2288,2293 ----
(entry->eflags & MAP_ENTRY_COW) == 0 ||
(entry->wired_count != 0)) {
! if ((fault_type & prot) !=
! (fault_type & ~VM_PROT_OVERRIDE_WRITE))
RETURN(KERN_PROTECTION_FAILURE);
}
Bruce
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