Keep debug info in a .sym file

Created by: dlrobertson

Problem:

When debugging the redox kernel, it is compiled without debug symbols which makes debugging difficult.

Solution:

Compile with debug info and place debug info in separate .sym file.

Changes introduced by this pull request:

• Compile time changes
  • Compile libkernel.a with debug info
  • Copy debug info to kernel.sym
  • Strip the kernel of debug symbols
• Workflow changes
  • Add debug option to make qemu

Drawbacks:

The kernel.sym can be large and libkernel.a is larger. kernel.sym is typically around 6 MB for me. It might be a good idea to put this behind a build option.

Blocking/related:

• redox-os/kernel#64

TODO:

• Write up a wiki page on debugging the redox kernel with qemu and gdb

Try it out:

To test this out first make sure that the redox-os/kernel#64 kernel is used, then rebuild the kernel. After rebuilding the kernel, run the VM and use make qemu debug=yes. Now it's time to crack open gdb

$ rust-gdb ./build/kernel
(gdb) target remote localhost:1234
(gdb) symbol-file ./build/kernel.sym
... other gdb commands
(gdb) continue

Go back to your VM and trigger the syscall you're interested in.