42 lines
1.7 KiB
Markdown
42 lines
1.7 KiB
Markdown
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# Kernel Documentation
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## Kernel shims
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Xenia implements all kernel APIs as native functions under the host.
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When a module is loaded, the loader will find all kernel imports, put a syscall in
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their place, then lookup a kernel export and link it to each import. The JIT will
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generate a sequence of instructions to call into Xenia's export if it encounters a syscall.
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Currently, there are two ways an export can be defined -
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[for example](../src/xenia/kernel/xboxkrnl/xboxkrnl_audio.cc):
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* `SHIM_CALL XAudioGetSpeakerConfig_shim(PPCContext* ppc_context, KernelState* kernel_state)`
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* `dword_result_t XAudioGetSpeakerConfig(lpdword_t config_ptr)`
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The `SHIM_CALL` convention is deprecated, but allows a closer look at the internals of how
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calls are done. `ppc_context` is the guest PowerPC context, which holds all guest
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registers. Function parameters are fetched from r3...r10 (`SHIM_GET_ARG_32`), and
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additional parameters are loaded from the stack. The return value (if there is one)
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is stored in r3 (`SHIM_SET_RETURN_32`).
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Details on how calls transition from guest -> host can be found in the [cpu documentation](cpu.md).
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The newer convention does the same, but uses templates to automate the process
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of loading arguments and setting a return value.
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## Kernel Modules
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Xenia has an implementation of two xbox kernel modules, xboxkrnl.exe and xam.xex
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### xboxkrnl.exe - Xbox kernel
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Defined under src/xenia/kernel/xboxkrnl.
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This is a slightly modified version of the NT kernel. Most of the APIs
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are equivalent to ones you'd find on MSDN or other online sources.
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Source files are organized into groups of APIs.
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### xam.xex - Xbox Auxiliary Methods
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Defined under src/xenia/kernel/xam.
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This module implements functionality specific to the Xbox.
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