[PR6580; patch for review] first step of unwind_cache enhancement

[Serguei Makarov]

The first incremental step to the runtime tweaks required to sanely implement PR6580. Namely, the kernel-side backtrace can be unwound one step at a time using _stp_stack_kernel_get, with the already unwound portion of the backtrace cached within the probe context.

This allows us to implement stack(n) (which returns the PC n levels deep within the stack) without having to resort to tokenizing a backtrace string each time.

The patch itself seems to be sound, but testing it drew attention to memory corruption errors in the existing DWARF unwinder (see PR14546).
-------------- next part --------------
A non-text attachment was scrubbed...
Name: uwcache.patch
Type: text/x-patch
Size: 12177 bytes
Desc: not available
URL: <http://sourceware.org/pipermail/systemtap/attachments/20120905/46bc395a/attachment.bin>