mov: move
sub: subtract
cmp: compare
cmpls: ls--->lower or same, le--->less or equal, hi--->higher
ldr: load register
lsl: logical shift left
str: store register
b: branch
bl: branch label, change pc
bne: branch not equal
beq: branch equal
blt: branch less than
push {r4, r5} : store r4, r5 to stack
pop {r4, r5}: restore r4, r5 from stack
ldm: load multiple
stm: store multiple
and:
ldrd r0, r1, [r2, #4] : load 8 bytes from r2 + 4, and high 4 bytes stored in r0, lower in r1
.align 2: 2 * 2 = 4, the ldr instruction we used to read memory only works at addresses that are multiples of 4
tst : compares two numbers by computing the logical and operation of the numbers, and then comparing the result with 0
strh reg,[dest]: stores the low half word number in reg at the address given by dest.
alias .req: reg sets alias to mean the register reg.
.unreq alias: removes the alias alias.
teq reg,#val: checks if the number in reg is equal to val.
========================================
| Register | Brief | Preserved | Rules |
|---|---|---|---|
| r0 | Argument and result | No | r0 and r1 are used for passing the first two arguments to functions, and returning the results of functions. If a function does not use them for a return value, they can take any value after a function. |
| r1 | Argument and result | No | |
| r2 | Argument | No | r2 and r3 are used for passing the second two arguments to functions. There values after a function is called can be anything. |
| r3 | Argument | No | |
| r4 | General purpose | Yes | r4 to r12 are used for working values, and their value after a function is called must be the same as before. |
| r5 | General purpose | Yes | |
| r6 | General purpose | Yes | |
| r7 | General purpose | Yes | |
| r8 | General purpose | Yes | |
| r9 | General purpose | Yes | |
| r10 | General purpose | Yes | |
| r11 | General purpose | Yes | |
| r12 | General purpose | Yes | |
| lr | Return address | No | lr is the address to branch back to when a function is finished, but this does have to contain the same address after the function has finished. |
| sp | Stack pointer | Yes | sp is the stack pointer, described below. Its value must be the same after the function has finished. |
========================================
movw 与 movt 指令
movw 与 movt 一般结合使用，用来往寄存器中加载一个 32 bit value。
环境：xcode 4.6.2，iPad 2， lldb
代码：
void ArmTest() {
asm (
"movw r1, #0xF8C4\n\t" // 1
"movt r1, #0x40\n\t" // 2
"mov r0, r0"
);
}
在函数的开始部分设置断点，
然后读取 r1 寄存器的值（register read r1）：r1 = 0x00000000
使用 ni 调试指令来继续执行一条指令，读取 r1 寄存器的值：r1 = 0x0000f8c4
继续单指令执行，读取寄存器值：r1 = 0x0040f8c4
可以得到结论：movw 将值加载到寄存器的低 16 位，movt 加载到高 16 位，合起来加载一个 32 bit value。
========================================
Register Alt. Name Usage r0 a1 First function argument Integer function result Scratch register r1 a2 Second function argument Scratch register r2 a3 Third function argument Scratch register r3 a4 Fourth function argument Scratch register r4 v1 Register variable r5 v2 Register variable r6 v3 Register variable r7 v4 Register variable r8 v5 Register variable r9 v6 rfp Register variable Real frame pointer r10 sl Stack limit r11 fp Argument pointer r12 ip Temporary workspace r13 sp Stack pointer r14 lr Link register Workspace r15 pc Program counter
========================================
movs 说明
movs r3, #0
cpsr {
0x30,
n = 0x0,
z = 0x0,
c = 0x0,
v = 0x0,
q = 0x0,
j = 0x0,
ge = 0x0,
e = 0x0,
a = 0x0,
i = 0x0,
f = 0x0,
t = 0x1,
mode = 0x10
}
执行后：
cpsr {
0x40000030,
n = 0x0,
z = 0x1,
c = 0x0,
v = 0x0,
q = 0x0,
j = 0x0,
ge = 0x0,
e = 0x0,
a = 0x0,
i = 0x0,
f = 0x0,
t = 0x1,
mode = 0x10
}
总之，movs 在 mov 的功能基础上影响标志位（zero位）。
=============================
bic 指令
bic Rd, Rn, Oprand2
BIC（位清除）指令对 Rn 中的值 和 Operand2 值的反码按位进行逻辑“与”运算。
BIC 是 逻辑”与非” 指令, 实现的 Bit Clear的功能
举例:
BIC R0, R0 , #0xF0000000
#将 R0 高4位清零
BIC R1, R1, #0x0F
#将R1 低4位清0
RSB 反向减法
Rn, Operand2
RSB（反向减法）指令可从 Operand2 中的值减去 Rn 中的值。
这是很有用的，因为有了该指令，Operand2 的选项范围就会更大。
例如:
RSB r4, r4, #1280
从1280中减去 R4
RSB R4, R0, #0×46
从0×46 中 减去 R0, 放入R4
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STM 与 LDM
STM和LDM的主要用途是现场保护、数据复制、参数传递等，其模式有8种，如下：
注：前面4种用于数据块的传输，后面4种用于堆栈操作
（1）IA 每次传送后地址加4
（2）IB 每次传送前地址加4
（3）DA 每次传送后地址减4
（4）DB 每次传送前地址减4
（5）FD 满递减堆栈
（6）FA 满递增堆栈
（7）ED 空递减堆栈
（8）EA 空递增堆栈
下面的讲述对于空递减堆栈和空递增堆栈同样适用.
在堆栈操作时，经常错误以为使用STMFD满递减将寄存器压入堆栈后，在弹出数据的时候应该使用LDMFA。
但是FD和FA仅用于指示目前操作的堆栈是何种模式(堆栈共有四种模式)，FD指明目前的堆栈是满递减堆栈，
则数据入栈时的指令为STMFD，那么数据出栈时的指令对应的为LDMFD，而不是LDMFA。
我们可以这样认为STMFD等价于STMDB，LDMFD等价于STMIA
那么，数据传输的顺序和数据入栈的顺序又是如何呢
先来看STMFD SP!,{R1-R3} 执行的结果图（操作之后SP指向SP'）
SP-------> |R3|
|R2|
SP'------>|R1|
那么STMFD SP!,{R3，R2，R1}执行后的堆栈顺序是不是刚好和上面的堆栈顺序相反，实际情况时这两个指令执行后的堆栈数据顺序一样，因为ARM编译器会自动将STMFD SP!,{R3，R2，R1}转换为STMFD SP!,{R0-R3}指令，也就是说，ARM编译器默认高寄存器优先存入堆栈。即便你在指令STMFD SP!,{R3，R2，R1}中刻意“安排”了寄存器入栈顺序，而在编译时编译器又重新做了处理，打乱了你期望的数据入栈顺序。
同理STMDB R0!,{R1-R3}和STMDB R0!,{R3，R2，R1}指令执行后数据在堆栈中的顺序完全一致。
STMFD SP!,{R1-R3}指令对应的出栈指令是LDMFD SP!,{R1-R3}（R1,R2,R3的顺序任意）
===================================
CBZ & CBNZ
比较，为零则跳转；比较，为非零则跳转。
可以使用 CBZ 或 CBNZ 指令避免更改条件代码标记并减少指令数目。
除了不更改条件代码标记外，CBZ Rn, label 与下列指令序列功能相同：
CMP Rn, #0
BEQ label
除了不更改条件代码标记外，CBNZ Rn, label 与下列指令序列功能相同：
CMP Rn, #0
BNE label
===================================
IT EQ /* if the EQ condition is true, (T)hen execute the next instruction */
MOVEQ r0, #1 /* note the redundant condition code, which needs to match the IT instruction */
------------------
ITE EQ /* if the EQ condition is true, (T)hen execute the next instruction (E)lse execute the instruction after it */
MOVEQ r0, #1
MOVNE r0, #0 /* note that the condition code must be inverted, since this is an "else" instruction */
===================================