I tracked this down to the code in linux-user/syscall.c. The mmap code seems broken, it assumes arg1 is a pointer to an array where the real arguments are. Given arg1 = 0 the memory access check fails.<div><br></div><div>The code I&#39;m working on will happily take mmap2 instead so I have a workaround. Does someone have an opinion on the state of the mmap code?</div>
<div><br></div><div> Kai<br><br><div class="gmail_quote">On Wed, Jun 17, 2009 at 8:54 PM, Kai Backman <span dir="ltr">&lt;<a href="mailto:kaib@google.com">kaib@google.com</a>&gt;</span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
I&#39;m running qemu-arm and see the following output from mmap with &#39;strace qemu-arm -strace&#39; (for both host and traget strace output):<br><div><font face="&#39;courier new&#39;, monospace">mmap(NULL, 32800, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x2ad329b46000</font></div>

<div><font face="&#39;courier new&#39;, monospace">4023 mmap(0,131072,7,34,-1,0) = 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 face="&#39;courier new&#39;, monospace">Program received signal SIGSEGV, Segmentation fault.</font></div>
<div><span style="font-family:&#39;courier new&#39;;font-size:10px">1: x/i $pc  0xce30:     ldr     r1, [r5]</span></div><div><font face="&#39;courier new&#39;, monospace">(gdb) i r</font></div>
<div><span style="font-family:&#39;courier new&#39;;font-size:10px">r5             0xfffffffe       -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 code should I start looking for how mmap works?</div>


<div><br></div><div> Kai</div><div><br><font color="#888888">--<br>Kai Backman, Software Engineer, <a href="mailto:kaib@google.com" target="_blank">kaib@google.com</a></font></div>
</blockquote></div><br><br clear="all"><br>-- <br>Kai Backman, Software Engineer, <a href="mailto:kaib@google.com">kaib@google.com</a><br>
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