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Re: kernel mprotecting my stack?

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Re: kernel mprotecting my stack?

Subject: Re: kernel mprotecting my stack?
From: Cyrus Harmon <email@hidden>
Date: Wed, 7 Feb 2007 09:43:24 -0800

No, only one machine and no KEXT involved here. 0xba01b80 is a right where I expect it to page, in the middle of the stack I allocate for this thread, BUT, for some reason this page seems to be mprotected:

(gdb) x/32w 0xba01b80 0xba01b80: Cannot access memory at address 0xba01b80 (gdb) x/32w 0xba00b80 0xba00b80: 0x00000000 0x00000000 0x00000000 0x00000000 0xba00b90: 0x00000000 0x00000000 0x00000000 0x00000000 0xba00ba0: 0x00000000 0x00000000 0x00000000 0x00000000 0xba00bb0: 0x00000000 0x00000000 0x00000000 0x00000000 0xba00bc0: 0x00000000 0x00000000 0x00000000 0x00000000 0xba00bd0: 0x00000000 0x00000000 0x00000000 0x00000000 0xba00be0: 0x00000000 0x00000000 0x00000000 0x00000000 0xba00bf0: 0x00000000 0x00000000 0x00000000 0x00000000 (gdb) x/32w 0xba02b80 0xba02b80: 0x00000000 0x00000000 0x00000000 0x00000000 0xba02b90: 0x00000000 0x00000000 0x00000000 0x00000000 0xba02ba0: 0x00000000 0x00000000 0x00000000 0x00000000 0xba02bb0: 0x00000000 0x00000000 0x00000000 0x00000000 0xba02bc0: 0x00000000 0x00000000 0x00000000 0x00000000 0xba02bd0: 0x00000000 0x00000000 0x00000000 0x00000000 0xba02be0: 0x00000000 0x00000000 0x00000000 0x00000000 0xba02bf0: 0x00000000 0x00000000 0x00000000 0x00000000

If the address were out of range, I could understand it, but in this case, it's in range and I can see the page above and the page below (although, I grant you, even the address is within the range I would expect, to 0x0's above and below it are very suspicious). But, still, it makes this rather hard to debug as I'm catching a fault in syscall and can't get a backtrace to figure out where I came from.

Thanks,

Cyrus

On Feb 7, 2007, at 9:29 AM, Garth Cummings wrote:

Hi Cyrus,
On Feb 6, 2007, at 5:47 PM, Cyrus Harmon wrote:
I'm not sure if this is really a kernel question per se, as it's motivated by user-space operations, rather than a KEXT or what not, but I'm getting an error like so:
[Switching to thread 11 (process 5245 thread 0x5803)]
0x90004d8a in syscall ()
(gdb) bt
#0  0x90004d8a in syscall ()
Cannot access memory at address 0xba01b80
Cannot access memory at address 0xba01b7c
If you're doing this bt from a two-machine kernel debugging session, that message usually means that the address is one not known to GDB because you haven't provided symbols covering that address.

If this is code in your KEXT, you need to create a symbol file for your KEXT and load that symbol file into GDB.
--gc
____________________________________________________________________
Garth Cummings					 email@hidden
Sr. Software Engineer
Apple Developer Technical Support
<http://developer.apple.com/technicalsupport>


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References:  
  >kernel mprotecting my stack? (From: Cyrus Harmon <email@hidden>)
  >Re: kernel mprotecting my stack? (From: Garth Cummings <email@hidden>)




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