bad/missing unwind information, which could result in libunwind
dereferencing bad pointers. This mechanism is based on msync(2) system
call and significantly reduces the chances of a bad pointer
dereference in libunwind.
The original idea was to turn this mechanism on only when necessary
i.e. libunwind didn't find proper unwind information for a IP.
There are a couple of problems in the current implementation.
* The flag is global and is modified without locking
* The flag isn't reset when starting a new unwind
The attached patch makes ->validate a per-thread setting by moving it
into struct cursor from unw_local_addr_space and resets it to false
when starting a new unwind. As a result, cursor->as_arg points to the
cursor itself instead of the ucontext (for the local case).
This was found to reduce the number of msync() system calls from an
application using libunwind significantly.
Signed-off-by: Paul Pluzhnikov <ppluzhnikov@google.com>
Signed-off-by: Arun Sharma <arun.sharma@google.com>
CFA should be incremented by 16 in the hope that the previous frame
may have valid unwind info.
Also increase the default frame pointer recognition heuristic from 4k
to 16k.
Signed-off-by: Andrey Veskov <Andrey.Veskov@intel.com>
Signed-off-by: Arun Sharma <arun.sharma@google.com>
a signal-trampoline, assume that it's a PLT stub.
If non-DWARF stepping fails to change IP and CFA, declare
it a bad frame.
2004/11/23 16:59:56-08:00 mostang.com!davidm
(unw_step): Also print IP as part of the function-trace.
2004/11/23 16:17:37-08:00 mostang.com!davidm
(unw_step): When dwarf_step() fails on a signal-frame, fill in all
the known locations because dwarf_step() fails on older
kernels which don't export the kernel vDSO even though every-
thing else may be providing proper DWARF unwind-info.
2004/10/25 17:43:57+02:00 homeip.net!davidm
Add Debug statement for return-value.
(Logical change 1.290)
In theory, this may not be needed. In practice, I find that
Red Hat Enterprise Linux AS release 3, the _start() routine has
no unwind-info, but we need to be able to unwind into this
routine to find the end-of-frame-chain marker (RBP == 0).
(Logical change 1.253)
