SVC举例

ARM64中svc 0x80的opcode=二进制

ARM64=AArch64中，SVC指令

• 指令格式=指令编码
  • 
• 指令语法
  • SVC #<imm>
    • imm=立即数
      • 16位的无符号数
      • 范围：0~65535
      • 内部对应bit位数：bit 20~5

-》所以此处的ARM汇编代码：

SVC 0x80

->

• imm= 0x80
  • 放到bit 20-5

加上其他固定bit位数，就是：

• bit 31-21：1101 0100 000
• bit 20-5：0000 0000 1000 0000
• bit 4-0：000 01

-》合并起来就是：

1101 0100 000 0000 0000 1000 0000 000 01

1101 0100 0000 0000 0001 0000 0000 0001

D4 00 10 01

• Little Endian
  • 01 10 00 D4
    • 011000D4
• Big Endian
  • D4 00 10 01
    • D4001001

-》即：

如此，才算真正搞懂：

（一般常见的默认的Little Endian的）ARM64=64位的ARM的svc 0x80的opcode=二进制，值是：011000D4

svc 0 -> Perform a syscall (syscall number x16 register)

下面以svc 0为例，说明svc指令典型的用法和流程：

• mov x0, x1 -> x0 = x1
• movn x0, 1 -> x0 = -1
• add x0, x1 -> x0 = x0 + x1
• ldr x0, [x1] -> x0 = *x1 -> x0 = address stored in x1
• ldr x0, [x1, 0x10]! -> x1 += 0x10; x0 = *x1(Pre-Indexing mode)
• ldr x0, [x1], 0x10 -> x0 = *x1; x1 += 0x10 (Post-Indexing mode)
• str x0, [x1] -> *x1 = x0 -> Destination is on the right
• ldr x0, [x1, 0x10] -> x0 = *(x1 + 0x10)
• ldrb w0, [x1] -> Load a byte from address stored in x1
• ldrsb w0, [x1] -> Load a signed byte from address stored in x1
• adr x0, label -> Load address of labels into x0
• stp x0, x1, [x2] -> x2 = x0; (x2 + 8) = x1
• stp x29, x30, [sp, -64]! -> store x29, x30 (LR) on stack
• ldp x29, x30, [sp], 64] -> Restore x29, x30 (LR) from the stack
• svc 0 -> Perform a syscall (syscall number x16 register)
• str x0, [x29] -> store x0 at the address in x29 (destination on right)
• ldr x0, [x29] -> load the value from the address in x29 into x0
• blr x0 -> calls the subroutine at the address stored in x0, store next instruction in link register (x30)
• br x0 -> Jump to address stored in x0
• bl label -> Branch to label, store next instruction in link register (x30)
• bl printf -> Call the printf function with arguments stored x0, x1
• ret -> Jump to the address stored in x30