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

[Kai Backman]

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

On Wed, Jun 17, 2009 at 8:54 PM, Kai Backman <address@hidden> 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

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Kai Backman, Software Engineer, address@hidden

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Kai Backman, Software Engineer, address@hidden