Shell detachment trick crashes on OS4

[koobo]

Hi,

Based on a crash report by @samo79 and with his assistance we discovered that HippoPlayer crashes when exiting on OS4 on a certain spot in the code.

It uses a "detachment" trick which was employed by some applications back in the day. It goes as follows:

• 1st code hunk cuts the segment list upon starting so that only the 1st hunk remains. It then creates a new process from the 2nd hunk and exits.
• The 1st segment is unloaded by OS.
• User sees in the shell that the app returned immediately and is now running. Handy!
• When exiting, the application unloads the remaining segments by itself. App exits without memory leaks.

The last step is a bit questionable since the app does an UnloadSeg and then continues running the code that was just possibly deallocated from memory. The remaining code closes the DOS library and exits, not much else. This part is then protected by Forbid to make it safe. Works fine on the classic OS! On OS4 the UnloadSeg call crashes.

Two questions:

• Just as an exercise, is something like this possible on OS4?
• How do I detect OS4 so that I can skip this technique during runtime? Check if the exec version is 50 or higher?

Also, I know next to nothing about OS4

[a/b]

jmp _LVOUnLoadSeg(a6) (or equivalent) must be the last instruction in the bootstrap code, you cannot close libs etc. after unloading, for obvious reasons.
If you stick with this, app should work on OS4. Unless they deliberately broke this feature (and a number of apps with it, eg. asm-one&co is using it).

[koobo]

Thanks! I heard that with this fix there's no total crash every time at exit anymore.