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capdl-loader-app: Refactor two-phase build design #56

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capdl-loader-app: Refactor two-phase build design #56

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Commits on Sep 1, 2023

  1. Remove seL4_lib dependencies from generated C spec 

    The capdl_spec.c file is generated by capDL-tool and is compiled into
the capdl-loader-app program to define the system that the loader will
load. The file is supposed to only be a C-language representation of the
capDL spec for a particular system.  Currently, the header files
required to compile this spec file introduces dependencies on a C
library, and libraries from seL4/util_libs and seL4/sel4_libs including
libsel4utils and libutils (and any libraries they depend on).

The spec itself doesn't inherently require any type definitions other
than what's provided by libsel4, and so it shouldn't require these
additional dependencies.

Signed-off-by: Kent McLeod <[email protected]>
    @kent-mcleod
    kent-mcleod committed Sep 1, 2023
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  2. capdl-loader-app: Introduce custom error checks 

    Instead of ZF_LOG* framework functions, we introduce our own layering of
functions that directly output to seL4_DebugPutChar() when the debug
syscall is present and outputs nothing when it isn't. This
implementation allows using a minimal amount of the muslc stdio
implementation for string formatting and bypasses the need for malloc or
any syscalls to be supported.

This will make it easier to refactor capdl-loader-app to be more
freestanding (minimal runtime dependencies) in upcoming commits.

Signed-off-by: Kent McLeod <[email protected]>
    @kent-mcleod
    kent-mcleod committed Sep 1, 2023
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  3. capdl-loader-app: Remove seL4_libs dependencies 

    Refactor the remainder of the implementation of capdl-loader-app to
remove seL4_libs dependencies. This is achieved by mostly using similar
basic constructions inline rather than relying on them being provided by
the external libs:

- Create inline definitions of seL4_ARCH_{invocation} for the arch being
  built,
- implement get_frame_object_type() which returns the correct object
  type for page sizes of the current architecture,
- provide a few macro definitions for basic definitions
- remove platsupport_serial_setup code as seL4_DebugPutchar() will be
  used for any console output for this app. (The loader doesn't safely
  handle accessing physical serial device untyped without potentially
  conflicting with resource requests of the system being loaded.
- remove malloc initialization as it is no longer required.

Signed-off-by: Kent McLeod <[email protected]>
    @kent-mcleod
    kent-mcleod committed Sep 1, 2023
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  4. capdl-loader-app: Refactor two-phase build design 

    The capdl-loader-app has previously used a non-conventional CMake
pattern for building. As the app is built with the capDL spec and ELF
files for any program data the loader is required to load, the actual
CMake target definitions are deferred until the targets for generating
the capDL spec are known as well as the ELF targets.  These are then
used to declare a capdl-loader-app target.

Instead this change uses a different approach:
- It compiles and links the program code leaving the symbols for the
  capDL spec and CPIO archive containing the ELF files unresolved, while
  still producing a base object file "capdl-loader.o".
- Later on, a complete image can be created by taking the CapDL C spec
  and an object file containing a CPIO archive of ELF files and
  compiling these with the "capdl-loader.o" file. This compilation can
  be done outside of a CMake build as only access to libsel4 and
  capdl-loader-app header files are required to compile the CapDL C
  spec.
- The helpers.cmake file that declares BuildCapDLApplication now builds
  the rootimage from within a custom command that performs the external
  call to a compiler with the required include paths and input files.
- the sel4runtime dependency is removed as the loader app doesn't
  require thread-local storage and basic entry point assembly code is
  provided by "entry.h" which sets up a stack and then directly calls
  main() as the kernel places the bootinfo pointer in the first argument
  register and this is all the capdl-loader program needs to bootstrap.
- As there is only one thread in the loader app, use global allocation
  instead of thread-local allocation for thread variables such as the
  pointer for the seL4 IPC buffer used by libsel4.

Signed-off-by: Kent McLeod <[email protected]>
    @kent-mcleod
    kent-mcleod committed Sep 1, 2023
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