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Demo: Hello, World at Five Heights

The same fourteen bytes, printed by programs written at five different levels of the stack.

Run

cd ../../../01-software-stack-full/demos/02-software-stack
make
make strace

./hello-nolibc         2 system calls
./hello-asm            30 system calls
./hello-c              35 system calls
./hello-cpp            65 system calls
python3 hello.py       6155 system calls

Then read two traces in full:

strace ./hello-nolibc
strace ./hello-c

And, one layer higher again:

python3 -m http.server 8080

Ask

  • The whole trace of hello-nolibc is three lines. What are the other thirty-three calls in hello-c doing?
  • All five end in the same write(). So what exactly is the extra cost buying?
  • Why does nobody write the two-system-call version?