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Virgil Dupras cdd0b64570 Modify userspace .org and RAMSTART expectations 
Instead of expecting a `USER_CODE` symbol to be set, we expect `.org` to be
set in all userspace glue code. This gives us more flexibility with regards to
how we manage that.

Moreover, instead of making `USER_RAMSTART` mandatory, we make it default to
the end of the binary, which is adequate in a majority of cases.

Will be useful for my upcoming mega-commit... :)
 		2019-11-15 10:33:13 -05:00
..
at28w Modify userspace .org and RAMSTART expectations 2019-11-15 10:33:13 -05:00
basic Modify userspace .org and RAMSTART expectations 2019-11-15 10:33:13 -05:00
ed Modify userspace .org and RAMSTART expectations 2019-11-15 10:33:13 -05:00
lib lib/parse: decimal ending with a whitespace are now valid 2019-11-13 22:10:06 -05:00
memt Modify userspace .org and RAMSTART expectations 2019-11-15 10:33:13 -05:00
sdct Modify userspace .org and RAMSTART expectations 2019-11-15 10:33:13 -05:00
zasm Modify userspace .org and RAMSTART expectations 2019-11-15 10:33:13 -05:00
README.md Modify userspace .org and RAMSTART expectations 2019-11-15 10:33:13 -05:00

README.md

User applications

This folder contains code designed to be "userspace" application. Unlike the kernel, which always stay in memory. Those apps here will more likely be loaded in RAM from storage, ran, then discarded so that another userspace program can be run.

That doesn't mean that you can't include that code in your kernel though, but you will typically not want to do that.

Userspace convention

We execute a userspace application by calling the address it's loaded into.

This means that userspace applications must be assembled with a proper .org, otherwise labels in its code will be wrong.

The .org, it is not specified by glue code of the apps themselves. It is expected to be set either in the user.h file to through zasm 3rd argument.

That a userspace is called also means that an application, when finished running, is expected to return with a regular ret and a clean stack.

Whatever calls the userspace app (usually, it will be the shell), should set HL to a pointer to unparsed arguments in string form, null terminated.

The userspace application is expected to set A on return. 0 means success, non-zero means error.

A userspace application can expect the SP pointer to be properly set. If it moves it, it should take care of returning it where it was before returning because otherwise, it will break the kernel.

Apps in Collapse OS are design to be ROM-compatible, that is, they don't write to addresses that are part of the code's address space.

By default, apps set their RAM to begin at the end of the binary because in most cases, these apps will be ran from RAM. If they're ran from ROM, make sure to set USER_RAMSTART properly in your user.h to ensure that the RAM is placed properly.