[Qemu-devel] Re: [PATCH] fix qruncom compilation problems

[Stefano Bonifazi <stefboombastic@gmail.com>]

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On 12/09/2010 08:16 AM, Paolo Bonzini wrote:
> On 12/08/2010 10:43 PM, Stefano Bonifazi wrote:
>>
>> Anyway running it with a com file as argument gave the error:
>>> mmap: Operation not permitted
>>
>
> You have to run it as root I think.
>
> Paolo
Thank you! Running as root worked, though it raises then the following 
error (from gdb) I am currently trying to understand:
> /home/stefano/LinuxDev/qemu-0.12.5/tcg/tcg.c:1367: tcg fatal error
>
> Program received signal SIGABRT, Aborted.
> 0x0012e416 in __kernel_vsyscall ()
Surely any hint on how to to fix this will be very welcome :)

I wish I could understand also what was wrong before, I mean /mmap/.. I 
understand you can't babysit me, but the gap between what one studies at 
university and the real world is very big and I feel lost :(
I've read pretty much about mmap trying to figure out myself but 
understanding how to map a file (what I could find in every article 
about mmap online) is not the same as understanding how it works inside 
QEMU ..
I know each process gets its own logical address space, if I understood 
fine mmap should take a portion of qruncom address space and give it to 
the emulator that should then see that as its own address space (please 
correct me if I am wrong!) ..
Now if I got fine the flag MAP_FIXED, obliges the process to give that 
portion of address space starting at its /addr/ parameter (the first).. 
or if it is not possible to give an error..
My big doubt is how can the process give exactly that portion of address 
space starting at zero by just  running it as root?.. I am expecting 
that area of address space to be taken by I dunno, code, data of the 
process itself.. honestly I don't know how things are allocated when a 
process is run(and I wish I could learn that).. but how can one think 
that addresses around zero are free for a mapping??
I'll appreciate very much any explanation, or links where to learn those 
topics! :)
Thank you very much!
Best Regards!
Stefano B.

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