Processes · execve and Scheduling

1. TODO 1 split the line into argv with strtok; end it with NULL
2. TODO 2 fork; in the child execvp, or print the error and _exit(127)
3. TODO 3 waitpid in the parent and report how the child ended
4. TODO 4 cd as a built-in with chdir
5. TODO 5 a trailing &: do not wait; collect later with WNOHANG

the finished shell (real session)

mysh> echo hello from a child
hello from a child
mysh> cd /tmp
mysh> pwd
/tmp
mysh> nosuchprog
mysh: nosuchprog: No such file or directory
[369 exited with status 127]
mysh> ./segv
[370 killed by signal 11]
mysh> sleep 1 &
[371 running in the background]
mysh> echo waiting
waiting
[371 done]

Think: why can cd not be a program like ls? (Hint: whose current folder would change?) Answer in your report.

1. TODO 1 in stack_starter.c: count the envp strings (a NULL-ended array, like argv)
2. TODO 2: point an Elf64_auxv_t * just past envp's NULL; print until AT_NULL
3. Compare with LD_SHOW_AUXV=1 ./stack; build with -static and compare AT_BASE
4. Predict the shares for nice 1, 5, 10, 19 from the weight table, then run ./shares N 5
5. Run ./ctxsw; find CONFIG_HZ of your kernel and explain the hog's number

expected output (our machine, real)

$ ./stack hello world
argc = 3
argv[0] at 0x7ffe5cfa2366 -> "./stack"
argv[1] at 0x7ffe5cfa236e -> "hello"
argv[2] at 0x7ffe5cfa2374 -> "world"
envp: 203 strings, …
auxv AT_PAGESZ          0x1000
auxv AT_PHDR  …         0x55f059196040
…
$ ./shares 5 5
nice 0 : 2.99 s CPU (75.4%)
nice 5 : 0.98 s CPU (24.6%)
$ ./ctxsw
sleeper  voluntary_ctxt_switches:  100
hog      nonvoluntary_ctxt_switches: 276

Report: a table predicted vs measured for task 4, and one sentence per difference larger than 1 %.