Commits on Sep 27, 2023

1. [Makefile] Add unoptimized build targets …

   Problem:
   When debugging xv6, many variables could not be examined and would
   return the message "optimized out". For example, in the `readi` function
   of `kernel/fs.c` the variable `m` is optimized out at various points of
   the debugging process:
   
       Breakpoint 1, readi (ip=.., user_dst=.., dst=.., off=.., n=..) at kernel/fs.c:477
       477       if(off > ip->size || off + n < off)
       (gdb) n
       479       if(off + n > ip->size)
       (gdb) n
       482       for(tot=0; tot<n; tot+=m, off+=m, dst+=m){
       (gdb) p m
       $1 = <optimized out>
       (gdb)
   
   Issue:
   Both the `qemu` and `qemu-gdb` targets in the Makefile build the kernel
   using the `-O` general optimization option for gcc. This is appropriate
   for a non-debug run of xv6, but causes problems viewing the content of
   variables that have been optimized out.
   
   Solution:
   Two new build targets are added to the Makefile:
   
   * qemu-noopt - Builds the xv6 kernel with optimization turned off
   * qemu-gdb-noopt - Builds the xv6 kernel with optimization turned off
     and starts qemu as a gdb server.
   
   This preserves the functionality of the original build targets while
   allowing the build of non-optimized kernels for debugging purposes.

   

   jjolly committed Sep 27, 2023
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