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Matheus
77 lines
1.1 KiB
NASM
77 lines
1.1 KiB
NASM
section .rodata
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extern syscall_libc_log
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func_count equ 1
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func_table:
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dq syscall_libc_log
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section .text
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global asm_syscall_entry
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; the registers for the system call are:
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; RETURN:
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; rax -> ret value
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; rdx -> errno
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; PARAM:
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; rax -> func
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; rdi, rsi, rdx, r10, r8, r9 -> parameters
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; clobbers: rax, rdx, rcx, r11
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asm_syscall_entry:
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swapgs
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xchg rsp, [gs:0] ; get new stack
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push qword [gs:0] ; save old stack
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mov [gs:0], rsp ; return back the kernel stack
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add qword [gs:0], 8 ; fix it
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push rcx ; old rip
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push r11 ; old rflags
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mov r11, 0x30 ; kernel data
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mov ds, r11
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mov es, r11
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; save C scratch registers
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; rax is not saved because it will be the return value
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; rdx is not saved because it will be the errno value
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push rdi
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push rsi
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push rcx
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push r8
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push r9
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push r10
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; system V C abi expects the third param to be in rcx
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; but the param is in rdx because of the syscall instruction
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mov rcx, rdx
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call [func_table + rax * 8]
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; now restore the scratch registers
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pop r10
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pop r9
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pop r8
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pop rcx
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pop rsi
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pop rdi
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; restore entry state
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mov r11, 0x40 ; user data
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mov es,r11
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mov ds,r11
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pop r11
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pop rcx
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pop rsp
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swapgs
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o64 sysret
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