On Wednesday 09 September 2009 10:39:30 Carlos O'Donell wrote: > On Sun, Jun 21, 2009 at 11:20 AM, John David > > Anglin<dave@xxxxxxxxxxxxxxxxxx> wrote: > > Looking at my email archive, I see the real cause involves kernel memory > > maps: > > > > > > > On Wed, May 06, 2009 at 01:39:49PM -0400, John David Anglin wrote: > > > > > > > The tombstone is: > > > > > > > > > > > > > > do_page_fault() pid=10205 command='strace' type=15 > > address=0x407d2f18 > > > > > vm_start = 0x4068d000, vm_end = 0x4068f000 > > > > > > > > > > > > So, the pointer passed to __canonicalize_funcptr_for_compare is > > outside > > > > the vm range. > > The strace problem is a compiler flaw. > > This is the problem: > * Strace examines the applications syscall. > * Strace extracts, via PTRACE, application addresses, addresses that > don't exist in the strace address space (and should not exist). > * Strace compares extracted address to a constant SIG_ERR. > * Compiler generates a call to __c_f_f_c, which dereference the > extracted address and strace faults. > > Strace and the application have completely different address spaces, > and __c_f_f_c can't assume that an address is in the current address > space. > > The solution is to detect that a comparison between two pointers is a > comparison between pointer and small constant, and avoid calling > __c_f_f_c for both. > > The workaround is to cast both long. I tested this and it works. I'll > submit this to debian as the fix. and include this explanation in a comment right above the cast ? ;) also, the strace list is active currently, so posting a patch there should get it merged (and since it's an important bugfix, it should get added before the next release). -mike
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