Re: UML fails to locate address space

From: linux-os (Dick Johnson)
Date: Tue May 20 2008 - 11:24:43 EST

On Tue, 20 May 2008, Jeff Dike wrote:

> On Tue, May 20, 2008 at 12:08:24PM +0100, Tom Spink wrote:
>> I've just recently pulled the latest GIT and compiled UML, however,
>> when I run it a message appears saying "Locating the top of the
>> address space... Address 0x0 no good?" and the program exits.
> Can you strace it and send me the output?
>> After some digging, it appears that page_ok is returning false when
>> checking 'bottom', in os_get_task_size
>> (arch/um/os-Linux/sys-i386/task_size.c:96). After running through
>> GDB, it seems that in line 31 of that file is where the segfault
>> occurs:
>> n = *address;
>> i.e. when trying to read from the address space (at address zero).
> The segfaults are on purpose - it will trap SIGSEGV and longjmp out of
> the handler and mark the affected address as not-usable.
> Jeff

Does this mean that I cannot mmap() address zero in the kernel
anymore? I should be able (in the kernel) read anything, and
then mmap() it to something usable in user-space. If address
zero is now artifically trapped there are problems being created
for no good reason at all.

Dick Johnson
Penguin : Linux version on an i686 machine (5588.29 BogoMips).
My book :

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