solutions

README.md

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+Recitation 8 - Solutions
+-----
+
+The answers to the questions are:
+
+1) 'x' starts in register $rdi and gets returned in $rax in function addone2. It is in memory location 0x7fffffffdfe8 in addone (The address value in addone may be slightly different depending on the student's machine but I have asked them to send screenshots of their work. As long as the address resembles the value mentioned here that is good enough for full credit)
+
+2) Instructions corresponding to line 12 are:
+
+```
+12      (*x)++;
+=> 0x0000000000400562 <addone+0>:   48 8b 07    mov    (%rdi),%rax
+   0x0000000000400565 <addone+3>:   48 83 c0 01 add    $0x1,%rax
+   0x0000000000400569 <addone+7>:   48 89 07    mov    %rax,(%rdi)
+```
+
+3) The instruction that causes the segmentation fault is:
+
+```
+=> 0x0000000000400562 <addone+0>:   48 8b 07    mov    (%rdi),%rax
+```
+
+The variable x holds the value 2, and x is a long *. This will clearly led to a segmentation fault when x is dereferenced. The specific instruction that does this is the one marked with the arrow: mov (%rdi),%rax. Trying to take the value at the address given by register %rdi, or trying to dereference x, causes the segmentation fault (line 27 of the source code to see the function call).