CS代写 ECE 391 Discussion

discussion_week_03

ECE 391 Discussion

Announcements & Reminders

! MP1 Due next Tuesday, Sep 14 at 5:59pm (commit on GitLab)
! Master branch for grading
! Don’t be late and show up to your assigned demo day!
! Rubric will be posted soon – ask if something is unclear

! Read the whole document carefully before you start – there’s a lot!
! Document suggests an order to write the functions
! Do NOT write the whole MP at once – write each IOCTL and then test it
! Demo questions will be based off of the documents and what you wrote

for the MP

int main() {
a = magic( 7, 8, 9);

Callee save regs – main

Return address for main

// int magic(int a, int b, int c)
// Performs magical operation on
// the input args

_____________

C Calling Convention

int binary_search(int key, int* array, int size);

return address

Int* array

EBP EBP + 4

Caller Saved Callee Saved

! A computer’s real-time clock (RTC) can generate interrupts at a
settable frequency

! Tasklets are interrupt handlers’ way of deferring work
! Interrupt handlers need to be as short as possible – why?

! In MP1, the tasklet is scheduled by the periodic RTC interrupt
! The tasklet is the main part of the MP1 game, which aggregates

information and updates the state of the game and the screen

Virtual Memory Issue

! Virtual memory allows each user-level program to have the illusion of
its own memory address space – why?

! When passing memory addresses between a user-level program and
the kernel, a translation is needed

! Translation is provided by mp1_copy_to_user and
mp1_copy_from_user

! If you improperly use them, things may still work in user space, but will
break in kernel space

Dispatcher

! Dispatcher does NOT modify the stack
! No need to setup stack frame
! Other functions don’t need to return to the dispatcher
! Use the JMP instruction instead of the CALL instruction for a function call –

return address

(previous stack)

! Debugging will be hard, especially in kernel
! Your code may run in user-space, but it may not run in kernel space
! In kernel mode, when it fails, it crashes everything
! Suggestion: identify issues in kernel mode, debug and fix in user

space; or comment out the IOCTLs and test one by one

Coding Style in x86 Assembly

bad_param:

Coding Style in C

! tmp1, tmp2, tmp3

! velocity_x, delta_y, acceleration_z

Magic Numbers

! Any number that appears in your code without a comment or a
meaningful name
! movl $1234, %ebx
! int i = 5678;

! If a number appears only once, you can use a comment
! cmpl $100, %ebx # loop for 100 times, so compare ebx with 100

! If a number appears more than once, define a constant (or make a
label if you are using x86 assembly)
! #define LOOP_COUNTER 100

! Note that the rules above does not apply to numbers that are used in
conventions. E.g. movl 8(%ebp), eax is fine, as everyone who knows C
calling convention should recognize the 8 in the code.

Other Things Related to Style

! No spaghetti code
! Don’t jump back and forth
! Keep programs and functions short – create helper functions

! Comments
! You have to comment your code
! But don’t comment on every line

! Function interface
! Every function you write must have an interface

程序代写 CS代考加微信: powcoder QQ: 1823890830 Email: powcoder@163.com

Related Posts