`get_isa()` in `get-stack.sh` does not handle all possible outputs of `uname -m`

[mpilgrem]

get_isa() in get-stack.sh is as follows:

# determines the the CPU's instruction set
get_isa() {
  if uname -m | grep -Eq 'armv[78]l?' ; then
    echo arm
  elif uname -m | grep -q aarch64 ; then
    echo aarch64
  else
    echo x86
  fi
}

get_isa() is used by is_x86_64() which, in turn, is used by do_distro() (called in the 'Linux' limb of do_os()).

get_isa() assumes that if the output of uname -m (the machine hardware name) is not armv6l, armv7l or aarch64 then it is x86_64 (or x86). However, this Wikipedia table indicates that other values are possible when uname -s (the kernel name) is Linux, including arm6l, sparc64,ppc64,i686,ppc,k1om, and 'mips.

It has been suggested that this is a 'bug waiting to happen'.

[HallowedDust5]

I think I can do this.

[HallowedDust5]

What exactly does the function return? Does it return the instruction set of the given cpu as provided by uname -m or does it return something else? What I'm asking is, what is the relation between the value returned by get_isa() and the value given by uname -m?

[mpilgrem]

I am not a 'scripter', but I think if you start at do_os() and 'work backwards', you will see the use made of the result of get_isa(). I think get_isa() needs to 'fail' if uname -m yields an unsupported machine architecture.

[HallowedDust5]

Oh that makes sense, thanks

[HallowedDust5]

Does the following code look good enough?

get_isa() {
  if uname -m | grep -Eq 'armv[78]l?' ; then
    echo arm
  elif uname -m | grep -q aarch64 ; then
    echo aarch64
  elif uname -m | grep -q x86 ; then
    echo x86
  else
    die "${uname -m} is not a supported instruction set"
  fi
}

I would have gone through and done checks for all the possible outputs for uname -m but it seemed like those checks wouldn't really do anything because I don't know where to check for what ISAs are supported.

[HallowedDust5]

I didn't open up a PR for this code because I wanted to make sure it's actually addressing the issue.

[mpilgrem]

It looks good to me, but with one question. I don't know much about sh scripts, but I read this: https://stackoverflow.com/questions/27472540/difference-between-and-in-bash. Is ${uname -m} what you need? Or is it $(uname -m)?

[HallowedDust5]

That's my Javascript coming out. Oops.