Commits on Nov 25, 2023

1. runtime: allow panic on syscall.Exit instead of halting …

   In some environments, such as u-root, code can be imported which
   provides a shell. The shell calls functions, instead of trying
   to use exec.Command (which is not available). An example
   can be found in github.com:u-root/u-root/tools/tinygobb.
   
   When the command exits, the shell needs to resume operation,
   which is not possible when runtime.Exit calls halt.
   
   On tamago, we achieve this by setting a normally nil
   function, runtime.Exit, to a funtion which panics. The
   shell has a recover() to catch the panics.
   
   There are many ways in which setting runtime.Exit can go wrong,
   including different functions setting it to different functions.
   
   tinygo allows a simpler, and hence more robust, model: instead
   of halting, we can panic. But in most cases, halting is ok.
   
   Add a function, runtime.PanicOnExit, which enables a panic
   on exit. This function is idempotent, and once panic on exit
   is enabled, it can not be disabled. This is restrictive
   by design. It is hoped that by making it simple and non-revocable,
   we can avoid the problems that can occur with more complex
   mechanisms, but still provide an option to halting.
   
   A function is provided, instead of just a variable, to allow
   simpler access from assembly, i.e., both variables and
   functions have been used in bare metal environments and, for
   several reasons, functions have proved more flexible.
   
   Signed-off-by: Ronald G. Minnich <[email protected]>

   

   rminnich committed Nov 25, 2023
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