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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 original name came from a previous hack the did not work but somehow
the old name remained. Now it was more misleading than anything else, so
let's rename it to something that is closer to what it actually does.
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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Originally I was planning to detect the machine model just in case we
needed to do workaround for special cases. But since apparently even
VisionFive2 brings its own CPU frequency base on DT, this is not even
needed. Hence, fetching the model is now a cool message being shown on
boot.
Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>
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If the 'timebase-frequency' property is available under the 'cpus' node
from the DTB blob, it makes sense to try to fetch this value from there
instead of hardcoding it. For other use-cases, where this information is
not available through DT (e.g. ACPI on the VisionFive2 board), we will
have to hardcode it with a default value even if it's not the proper
one.
Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>
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As part of a shameful hack I was tampering with the 'ra' register as
well as with the 'sepc' CSR. Since in the end we just assume 'sret' is
in place at the end, let's be cleaner and leave 'ra' alone.
Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>
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This allows this functionality to be properly extracted for unit tests.
Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>
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We actually don't need to preserve the initially computed base address
for each binary, but we can just preserve the final entry address.
Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>
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Scheduling is easier if there is an init process which does nothing.
This way we don't have to perform hacks in order to idle in S privilege
mode while touching special registers in weird ways.
For now this process is kind of costly since 'wfi' is not accepted in
this context, but this can be further tuned down in the future by
setting TW=1 on 'mstatus', or by handling the exception and allowing it
if it comes from the proper process.
All of that being said, there is still work to be done as things fail
when optimitzations are on.
Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>
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This allows us to actually catch system calls and start to run user
space programs. That being said, the whole thing is still pretty
brittle, and the scheduler is not quite there yet.
Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>
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In commit 573a8c6b490a ("usr: Rename foo/bar to fizz/buzz") the path of
the user-space binaries have changed. The `initrd` parsing code makes
some decisions based on that naming, and so it needed to be updated as
well.
Fixes: 573a8c6b490a ("usr: Rename foo/bar to fizz/buzz")
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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We expect a CPIO archive with the 'newc' format for the initrd. Parse
this archive from the given initrd address and fetch the address for
each ELF executable while also pairing which task correspond to which
ELF.
This commit leaves to do the actual parsing of the ELF file for each
task, while also leaving some string utilities to be refined.
Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>
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The kernel entry has a pointer to the DTB blob as a parameter. From this
pointer we can parse the the DTB blob to find the properties
"chosen->linux,initrd-start" and "chosen->linux,initrd-start". These
properties are guaranteed to have 64-bit addresses which point where the
initrd is in memory, which we need to fetch the binaries to be loaded.
Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>
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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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