more fillin of proj0.txt

1 files changed, 26 insertions, 3 deletions

diff --git a/proj0.txt b/proj0.txt
index 5052dfa..c4aa3dc 100644
--- a/proj0.txt
+++ b/proj0.txt
@@ -80,12 +80,33 @@ and fulfills the needs of project0.
 >> `struct' member, global or static variable, `typedef', or
 >> enumeration.  Identify the purpose of each in 25 words or less.
 
+struct start_aux_data:
+char *args  ...renamed from filename to args as we strip off the executable name
+               early and only store the commandline arguments
+
 ---- ALGORITHMS ----
 
 >> A2: Briefly describe how you implemented argument parsing.  How do
 >> you arrange for the elements of argv[] to be in the right order?
 >> How do you avoid overflowing the stack page?
 
+First we strip off the executable name from the command string and pass it to
+thread_create(). Thus we name threads by their executable.
+After passing the arguments through start_process(), load() and setup_stack()
+we first copy the whole arguments byte array following the executable name onto
+the stack. Afterwards we align the current stack address and proceed with
+creating the argv[]-pointers by walking through the already copied arguments
+in reverse order. This way we can replace all space characters with 0-characters
+and at the same time detect the start of every argument which we push onto the
+stack. Additional we check for possible stack overflow. The walking order is
+already the correct order necessary for the argv[]-pointers on the stack.
+As a last step we push the address of the executable name, the address of the
+argv[] itself, the number of commandline arguments and a fake return addres
+onto the stack.
+
+Overflowing is avoided calculating the end of the stack and checking the
+current stack pointer after every push of an argv[]-pointer entry.
+
 ---- RATIONALE ----
 
 >> A3: Why does Pintos implement strtok_r() but not strtok()?
@@ -96,7 +117,10 @@ strtok() uses global data, so it is unsafe in threaded programs such as kernels.
 >> and arguments.  In Unix-like systems, the shell does this
 >> separation.  Identify at least two advantages of the Unix approach.
 
-
+* Possible bugs in the code will either just break the shell or allow code
+  execution with user privileges. Otherwise this could lead to a kernel oops
+  or even worse code execution within the kernel.
+TODO
 
                            SURVEY QUESTIONS
                            ================
@@ -122,5 +146,4 @@ the quarter.
 
 >> Any other comments?
 
-
-
+TODO