Dear All,

    Some students have had trouble installing GDB on their Mac OS El 
Capitan systems, due to these systems' "SIP" features. I updated
instructions in the intro notes in the class directory with some
relevant links (look for the parts marked "[UPDATE:]").

    An alternative is to use LLDB, which comes installed with Xcode.
LLDB uses a somewhat different command language from GDB, and
its disassembler style, in my opinion, is less informative; still,
you don't need to do any extra work to install it, and most GDB
commands, in fact, work.

    To translated between LLDB and GDB is summarized here:
http://lldb.llvm.org/lldb-gdb.html . For example, do disasm
a function, in LLDB you say "disas -n main" or "disas -n puts";
to view registers, "reg r", to write 4 bytes memory into memory,
"mem w -s 4 addr value", etc. Breakpoints and single-instruction
stepping work approximately the same as in GDB, with the difference
that GDB breaks past the function preamble, while LLDB breaks before
it, and you need to step through these to get the right value of
the base pointer RBP and stack pointer ESP.

    Thanks,

--Sergey