44 lines
1006 B
NASM
44 lines
1006 B
NASM
; Generic high-level syscall handler
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[EXTERN syscall_handler]
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; Low-level interrupt based system call entry function
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[GLOBAL syscall_entry]
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[SECTION .text]
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; The SystemV ABI for x64 uses the register `rdi`, `rsi`, `rdx`, `rcx`, `r8` and
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; `r9` to pass the first six parameters of a function. Since every syscall can
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; have a maximum of 5 parameters, these register will just be forwarded (without
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; requiring any additional operation), having the syscall number stored in `rdi`.
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; The return value will be stored in `rax`.
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ALIGN 8
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syscall_entry:
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; Interrupt Context Pointer (7th Parameter)
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push rsp
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; Clear direction flag for string operations
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cld
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; Call the high-level (C++) system call handler
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sti
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call syscall_handler
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cli
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; Optional: Prevent kernel information leakage
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; by zeroing scratch registers
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mov rdi, 0
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mov rsi, 0
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mov rdx, 0
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mov rcx, 0
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mov r8, 0
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mov r9, 0
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mov r10, 0
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mov r11, 0
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; Drop 7th parameter
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add rsp, 8
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; Return from interrupt entry function
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iretq
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