[Bug uprobes/10836] uprobes-provided pt_regs* are unreliable

[mjw at redhat dot com]

------- Additional Comments From mjw at redhat dot com  2009-10-28 12:29 -------
This is also a problem for the dwarf based unwinder.

In runtime/unwind.c we feed unwind_frame() a pt_regs struct describing the
current state of the registers (plus some unwind tables, stp_module, etc.) Then
that uses its internal unwind_state regs stack to keep track of what is going to
happen with the pt_regs given the cfa ops found in the table. And when it is all
processed it spits out a new pt_regs struct describing the state of one unwind
step. In runtime/stack-<arch>.c we are feeding unwind_frame() initially the
pt_regs given by either kprobes or uprobes (arch_unw_init_frame_info(&info,
regs)). But the uprobes pt_regs are the "wrong kind" for user space although the
do work most of the time.

This could be fixed without having to change much by having the "loony concept"
of synthesized pt_regs without having to change too much of this code. Otherwise
we would need to make arch_unw_init_frame_info() smarter and detect we want the
user space registers (which we know in stp_stack_print because tsk != NULL) and
use the appropriate regsets to instantiate the unwind_info->regs.

-- 


http://sourceware.org/bugzilla/show_bug.cgi?id=10836

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