adding notes for gdb

diff --git a/gdb/index.mdwn b/gdb/index.mdwn
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+Debugging with gdb
+==================
+
+Our Demo Code:
+
+    #include <stdio.h>
+    #include <stdint.h>
+
+    int g_myvar = 42;
+    #define MYCONST 99
+
+    void sideeffect(void){
+        g_myvar += MYCONST;
+    }
+
+    uint8_t myfunction(uint8_t x){
+        return x+42;
+    }
+
+    int main(void){
+
+        uint8_t foo = 23;
+        uint8_t bla = 23;
+
+        uint8_t x = foo + bla;
+        uint8_t i;
+
+        uint8_t y = myfunction(bla);
+
+        uint8_t * verybad = 0;
+        
+        printf("%d\n", foo);
+        printf("%d\n", y);
+        // use this printf to cause a segfault
+        // printf("%d\n", *verybad);
+
+        for(i = 0; i < 10; ++i){
+            y = myfunction(y);
+            sideeffect();
+        }
+        printf("%d\n", y);
+
+
+        return 0;
+    }
+
+Resources
+---------
+
+* Vorlesungsfolien Betriebssysteme UE auf der TU Wien:
+[Debugging](http://ti.tuwien.ac.at/cps/teaching/courses/osue/slides/ss14_entwicklung_in_c.pdf)
+* Online Tutorial auf [beej.us](http://beej.us/guide/bggdb/)
+
+Basics
+------
+
+* gcc -g test.c -o test
+* gdb test
+* gdb test core
+* gdb --args
+
+Commands in GDB
+---------------
+
+* break
+* continue
+* next
+* info breakpoints
+* watch
+* list
+* print
+* bt full
+* catch signal
+* run
+* break .. if ...
+* delete
+* disable
+* enable
+* step
+* stepi
+* target record-full
+* reverse-next
+* set
+* quit
+
+Show preprocessor macros
+------------------------
+
+See [Thread on
+SO](http://stackoverflow.com/questions/2934006/how-do-i-print-a-defined-constant-in-gdb)
+
+    gcc -g3 test.c
+    gdb a.out
+    (gdb) info macro MYCONST
+    (gdb) macro expand MYCONST
+
+Fun with print
+--------------
+
+* print myfunction(y+23/7)/23.0
+* print printf("%d\n", 23 > 42 ? 111 : 222) 
+
+
+Enable history
+--------------
+
+create a file .gdbinit in ~ and put this line in:
+
+    set history save on
+