17299f0734
We have a collection of python scripts that are part of our build system. This PR collects docstring comments added to these scripts into a summary document. Previous references to just the script name in other documentation are updated to point to this build tool documentation. Some of the scripts needed an update to be processed (via include directives) consistently. Signed-off-by: David B. Kinder <david.b.kinder@intel.com> Signed-off-by: Anas Nashif <anas.nashif@intel.com>
26 lines
1.2 KiB
ReStructuredText
26 lines
1.2 KiB
ReStructuredText
.. _mpu_userspace:
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MPU Backed Userspace
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####################
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The MPU backed userspace implementation requires the creation of a secondary
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set of stacks. These stacks exist in a 1:1 relationship with each thread stack
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defined in the system. The privileged stacks are created as a part of the
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build process.
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A post-build script :ref:`gen_priv_stacks.py` scans the generated
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ELF file and finds all of the thread stack objects. A set of privileged
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stacks, a lookup table, and a set of helper functions are created and added
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to the image.
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During the process of dropping a thread to user mode, the privileged stack
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information is filled in and later used by the swap and system call
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infrastructure to configure the MPU regions properly for the thread stack and
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guard (if applicable).
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During system calls, the user mode thread's access to the system call and the
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passed-in parameters are all validated. The user mode thread is then elevated
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to privileged mode, the stack is switched to use the privileged stack, and the
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call is made to the specified kernel API. On return from the kernel API, the
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thread is set back to user mode and the stack is restored to the user stack.
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