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Date: Wed, 17 Jun 2009 20:54:33 +0300
Message-ID: <c7187c3d0906171054m7037bf78va250ec93a6b580e8@mail.gmail.com>
From: Kai Backman <kaib@google.com>
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Subject: [Qemu-devel] problems with mmap on qemu-arm
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I'm running qemu-arm and see the following output from mmap with 'strace
qemu-arm -strace' (for both host and traget strace output):
mmap(NULL, 32800, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) =
0x2ad329b46000
4023 mmap(0,131072,7,34,-1,0) = 0xfffffff2

When my program later tries to read memory at 0xfffffffe it fails with a
SIGSEGV:
Program received signal SIGSEGV, Segmentation fault.
1: x/i $pc  0xce30:     ldr     r1, [r5]
(gdb) i r
r5             0xfffffffe       -2

Why does qemu-arm return such high addresses on a 32 bit platform and why is
the memory inaccessible? If this doesn't seem like an obvious bug in my
code, where in the qemu code should I start looking for how mmap works?

 Kai

--
Kai Backman, Software Engineer, kaib@google.com

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I&#39;m running qemu-arm and see the following output from mmap with &#39;s=
trace qemu-arm -strace&#39; (for both host and traget strace output):<br><d=
iv><font face=3D"&#39;courier new&#39;, monospace">mmap(NULL, 32800, PROT_R=
EAD|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) =3D 0x2ad329b46000</font>=
</div>
<div><font face=3D"&#39;courier new&#39;, monospace">4023 mmap(0,131072,7,3=
4,-1,0) =3D 0xfffffff2</font></div><div><br></div>
<div>When my program later tries to read memory at 0xfffffffe it fails with=
 a SIGSEGV:</div><div><div><font class=3D"Apple-style-span" face=3D"&#39;co=
urier new&#39;, monospace">Program received signal SIGSEGV, Segmentation fa=
ult.</font></div>
<div><span class=3D"Apple-style-span" style=3D"font-family: &#39;courier ne=
w&#39;; font-size: 10px; ">1: x/i $pc =A00xce30: =A0 =A0 ldr =A0 =A0 r1, [r=
5]</span></div><div><font class=3D"Apple-style-span" face=3D"&#39;courier n=
ew&#39;, monospace">(gdb) i r</font></div>
<div><span class=3D"Apple-style-span" style=3D"font-family: &#39;courier ne=
w&#39;; font-size: 10px; ">r5 =A0 =A0 =A0 =A0 =A0 =A0 0xfffffffe =A0 =A0 =
=A0 -2</span></div></div><div><br></div><div>Why does qemu-arm return such =
high addresses on a 32 bit platform and why is the memory inaccessible? If =
this doesn&#39;t seem like an obvious bug in my code, where in the qemu cod=
e should I start looking for how mmap works?</div>

<div><br></div><div>=A0Kai</div><div><br>--<br>Kai Backman, Software Engine=
er, <a href=3D"mailto:kaib@google.com" target=3D"_blank">kaib@google.com</a=
></div>

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