linux-kernel - Re: UML fails to locate address space

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Message-ID: <7b9198260805200659p6ed28403t9b0b0ea995f158d5@mail.gmail.com>
Date:	Tue, 20 May 2008 14:59:14 +0100
From:	"Tom Spink" <tspink@...il.com>
To:	"Jeff Dike" <jdike@...toit.com>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: UML fails to locate address space

2008/5/20 Jeff Dike <jdike@...toit.com>:
> 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?

Attached.  I guess the line of interest is:

mmap2(NULL, 4096, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = -1 EACCES (Permission
denied)

>
>> 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.

I gathered that much - I was just letting you know which test it was
that was failing.

>
>                  Jeff
>

Thanks!

-- 
Tom Spink

Download attachment "uml-strace" of type "application/octet-stream" (2978 bytes)