Re: [Qemu-devel] Re: problems with mmap on qemu-arm

[Riku Voipio <riku.voipio@iki.fi>]

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On Wed, Jun 17, 2009 at 11:38:32PM +0300, Kai Backman wrote:
>    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.
>    The code I'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?
>     Kai

looking at old_mmap() for arm in kernel, qemu seems to the right thing. Ie
you are probably calling mmap the wrong way, you are supposed to give it a
array.

mmap syscall is depreceated, glibc uses mmap2 since forever.

>    On Wed, Jun 17, 2009 at 8:54 PM, Kai Backman <[1]kaib@google.com> wrote:
> 
>      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, [2]kaib@google.com
> 
>    --
>    Kai Backman, Software Engineer, [3]kaib@google.com
> 
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