Clarification in Lecture 18 alltraps definition

[Santosh K P]

Hello,

In trapasm.s, in definition of alltraps , there're 2 consecutive instructions
pushl %esp
call trap
In Lecture 18(46:41), it's mentioned that the esp is being pushed because pushal doesn't push esp register.
But following document says that pushal also pushes esp register.

https://pages.hep.wisc.edu/~pinghc/x86AssmTutorial.htm

It seems the purpose of the statement pushl %esp is to provide argument (in accordance with gcc function calling conventions) to trap()(in file trap.c), which takes trapframe pointer as an argument

Can you please confirm if this is correct?

Sincerely,
Santosh K P

[Parth Dhar]

Yes, that is indeed correct. A comment from the same line from the latest version of the code listing (https://iitd.github.io/os/nptel21/xv6.pdf):

# Call trap(tf), where tf=%esp

pushl %esp

call trap