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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 <mikisabate@gmail.com>
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The halting in secondary harts should not be treated too differently as
with the (unlikely) scenario that the main function quits. Hence, merge
the code in both cases.
Moreover, we do not really need to to initialize the values of most
registers, as they will be explicitely set when needed anyways.
Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>
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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 <mikisabate@gmail.com>
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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 <mikisabate@gmail.com>
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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 <mikisabate@gmail.com>
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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 <mikisabate@gmail.com>
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On 'printk' and 'sys_write' calls, prepend the name of the task that is
being executed for each message. This is an easy way to show off that we
are doing the right thing with the 'tp' register, even if we don't do
much with it.
Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>
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The notion of 'scheduling' a process on this kernel is effectively the
same as starting the process anew. This is pretty bananas for any
general purpose kernel, but this is not our case.
Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>
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In order to run on real hardware, it's actually easier to re-use
workflows from existing bootloaders than loading things in memory
manually. In order to achieve this two things had to be settled:
1. The image has to have a Linux header as defined in the RISC-V port.
This header will be taken into consideration by bootloaders in order to
know where to jump, the image offset, the endianness of the image, etc.
2. The image cannot just be an ELF executable. Rather, we must translate
it into binary form via `objcopy`.
With all of this at hand, I was able to make the kernel run on a
Starfive VisionFive 2 board, and I have recorded an example so it's
available as documentation.
Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>
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A basic interrupt handler has been implemented which tracks the seconds
that have been elapsing along the way. Depending on the value of these
seconds, then a task has to be called.
Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>
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The given initrd is a CPIO archive of multiple ELF executables. We are
already able to parse the CPIO archive to detect where each file is
located, this commit adds the mapping for each ELF executable to the
corresponding task_struct.
Note that this is still heavily under construction, since we cannot
simply jump into the entry point of an executable as we have not yet
setup the proper layout from performing context switches.
Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>
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Bootstrap an init task which holds at least the initial stack that is to
be used when setting up the registers (such as `sp` and `tp`).
In order to guarantee that the stack and the rest of the registers are
set up correctly, this commit also provides a raw implementation of a
`printk` function.
Moreover, this commit also adds an argument that must be passed to
`start_kernel`, which is the pointer to the embedded `fdt` blob. This
argument will be used by later work so to fetch, at least, the base
address for the initial ram disk. This was also used to test that the
stack was working as expected.
Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>
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For now the base layout has been defined and we have a binary that is
properly reached through openSBI.
Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>
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