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46 lines
1.3 KiB
Markdown
46 lines
1.3 KiB
Markdown
# OS on Kaleid Documentation
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## System calls in Kaleid kernel
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Copyright © 2018-2021 The OS/K Team
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|  | Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License|
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### System call ABI
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System calls take arguments and return values from/by classical System V ABI
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registers
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#### Arguments
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rdi : system call code
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rsi : first argument
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rdx : second argument
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r10 : third argument
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#### Return value
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rax : an error_t value
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### System call vector
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In OS/K, system calls are triggered by an userspace program using a software
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interrupt vector 0x80.
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In assembly language that means using `int 0x80`
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That vector is directly registered in the IDT : it *does not* use the ISR
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inscription function (`error_t KeRegisterISR(void (*isr)(ISRFrame_t *regs), uchar
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isrNo)`), thus a device driver can't replace the syscall handler.
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#### Pre-handler
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When int 0x80 is triggered, following the IDT, the pre-handler `syscallPreHandler`
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takes control. The role of that pre-handler is mainly context-switching related
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before the actual system call takes place.
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#### Syscall handler
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`error_t _KeSyscallHandler(ulong code, ISRFrame_t *regs)` is called by the
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pre-handler and actually get parameters
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