fbos/include, branch main

Add a note on HSM

2024-12-05T13:03:09Z

The hart lottery that we do on initialization is a bit rigged. Write a note on that in the documentation of the 'hart_lottery' variable. Signed-off-by: Miquel Sabaté Solà

Pass the hart ID on start_kernel instead

2024-12-04T16:23:57Z

Instead of storing the hard ID as given by the bootloader into a C variable, pass it directly into the 'start_kernel' function since we don't need to tamper the value as originally laid out on the 'a0' register. Signed-off-by: Miquel Sabaté Solà

Move documentation to the proper places

2024-12-04T13:23:44Z

Code documentation was scattered between header and source files. Since the norm was already to have this documentation into header files, move some comments from source files to their header counterparts. This hopefully makes things more consistent. Signed-off-by: Miquel Sabaté Solà

Write down the requirement for the Zaamo extension

2024-12-03T13:56:17Z

Since 2eead36f97fa ("Run a hart lottery on SMP") the kernel is making use of the 'amoadd.w' instruction, which requires the Zaamo extension (included in the base A extension). This is notable and is worth a mention on the list of requirements. Signed-off-by: Miquel Sabaté Solà

Run a hart lottery on SMP

2024-12-03T13:34:43Z

On systems with SMP multiple harts will try to run the kernel, and they will appear at random. But in this kernel, in order to keep things simple, we want to make sure that *only one* hart is running the show, as it greatly simplifies things on these kinds of systems. The solution is similar to what Linux does, which is to allow the first hart to initialize things, but then (and different to what Linux does), it will infinitely stall all the other harts that arrive at a random later point in time. In order to make this more apparent, I have also added a print message showing which hart is being used to run the whole thing. Signed-off-by: Miquel Sabaté Solà

Remove stack pointer for each process

2024-12-03T06:59:01Z

Since 6132623dbf30 ("Share the same stack everywhere") the same stack is used everywhere. Hence, it's rather pointless for each task to have a pointer to a stack which is the same and that is never read. Signed-off-by: Miquel Sabaté Solà

Simplify how we fetch the load address

2024-12-03T06:47:56Z

Similarly to 58fcecc381be ("Simplify the constant on the size of the stack"), the base and offset load addresses where taken from the Linux kernel, which has to account for way more stuff than this poor kernel. Hence, let's be more explicit about the base address and the offset where the kernel will be located, so it's actually more clear both on the linker, and on the kernel's header. Signed-off-by: Miquel Sabaté Solà

Simplify the constant on the size of the stack

2024-12-03T06:41:45Z

At the beginning I carried over things from the Linux kernel just in case I would need them in the future. As this project is very much at a stage where I'm already happy with it, let's remove unneeded complexity. Signed-off-by: Miquel Sabaté Solà

Don't repeat the task name when printing the model

2024-12-02T20:09:54Z

When printing the initial model message on DEBUG it repeated the "init" message twice. Avoid that by directly using 'write' on some of the calls. Fixes: 32e880127366 ("Prepend the name of the task on debug") Signed-off-by: Miquel Sabaté Solà

Share the same stack everywhere

2024-12-02T20:02:35Z

As documented in the code, we are not implementing any kind of memory protection, so in theory any process (regardless if running in user or kernel space) would be able to tamper with other processes' stack. Hence, don't even pretend that we are separating stacks and share the same global stack everywhere. This simplifies things a bit. Signed-off-by: Miquel Sabaté Solà