gdb on Mac OS bpt implementation question

Jason Molenda jmolenda@apple.com
Thu Nov 10 22:19:00 GMT 2011


On Nov 8, 2011, at 3:41 PM, Mick Jordan wrote:

> I'd be grateful if someone could point me to where in the gdb source code that Mac OS specific breakpoint setting is done. The problem I am trying to resolve is how breakpoints are set in shared libraries, given that they are loaded read-only on Mac OS X (assuming the "write a bpt instruction" approach).


For what it's worth, two other implementations that may be worth consulting on issues like this are the Apple fork of gdb, downloadable here
	http://opensource.apple.com/
although it's based on the gdb sources circa 2006-2007.


lldb, the new debugger that we've been writing recently is licensed under the LLVM copyright (berkeley-style) and has a public svn repository, is also a good reference for how debuggers work on the Mac OS X platform.  v.
	http://lldb.llvm.org/

although note that lldb's primary method of operation on Mac OS X is to debug the inferior via a gdbserver-like program via gdb remote protocol (our implementation is "debugserver" and the sources are in lldb/tools/debugserver in the source checkout).  Originally we had lldb controlling the inferior process directly but on Mac OS X we've moved away from that and have all process done by debugserver - that's where you'd want to look to see how the low level memory reading/writing/etc is done.


Jason



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