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OS on Kaleid Documentation

System calls in Kaleid kernel

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System call ABI

System calls take arguments and return values from/by classical System V ABI registers

Arguments

rax : system call code rdi : first argument rsi : second argument rdx : third argument rcx : fourth argument

Return value

rax : an error_t value

System call vector

In OS/K, system calls are triggered by an userspace program using a software interrupt vector 0x80. In assembly language that means using int 0x80

That vector is directly registered in the IDT : it does not use the ISR inscription function (error_t KeRegisterISR(void (*isr)(ISRFrame_t *regs), uchar isrNo)), thus a device driver can't replace the syscall handler.

Pre-handler

When int 0x80 is triggered, following the IDT, the pre-handler syscallPreHandler takes control. The role of that pre-handler is mainly context-switching related before the actual system call takes place.

Syscall handler

error_t _KeSyscallHandler(ulong code, ISRFrame_t *regs) is called by the pre-handler and actually get parameters

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