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Re: ReBranch - a record-replay debugging tool


Is it something like you do an instrumentation in object code....mostly at all 
control flows and system calls.
and record some things.
so indirectly you do not record every instruction, but you need to modify object 
code by binary instrumentation.

but what I fail to understand is; what all do you record ?


----- Original Message ----
From: Nan Wang <>
To: Pedro Alves <>;
Sent: Thu, June 9, 2011 10:09:09 PM
Subject: Re: ReBranch - a record-replay debugging tool

What I mean "control-flow only debugging" is:

Sometimes user only use GDB's control-flow functions, such as 'c', 'b',
'n', 's' ... to watch how the program get to the bug. He or she doesn't
care the variable name, the memory and some data-flow information.

ReBranch demands "control-flow only debugging" because it only records
every branch instruction. In current implementation (the modified
version of gdbserver), the replayer still need to create a process and
use ptrace to control it. When data-flow have error (caused by data-race
in multi threading situation), the ptraced process will generate
segfault for every instructions, which slows down the performance.

ReBranch have a GUI replayer -- ReBranchK -- which is a simple
control-flow-only debugging tool. ReBranchK doesn't really create the
process and debug it. It 'executes' the program virtually by reads the
log and shows corresponding source code. It implements 's', 'b' and 'c'
command. However, when writing ReBranchK, I found that, without stack
information, many useful control-flow command such as 'n' and 'bt' are
hard to be implemented. Therefore, I hope someone help me to put this
"control-flow only debugging" function into gdbserver.
> Can you clarify what do you mean by "control-flow only debugging"?
> (Note: I haven't had the time yet to read your document on ReBranch,
> so I don't really know how it works or why would you need gdbserver
> for replay)

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