[英]Loading 32 bit values to a register in arm assembly
I want to load 1 32 bit hexadecimal directly into a register using arm assembly.我想使用 arm 组件将 1 个 32 位十六进制直接加载到寄存器中。
mov r1,#0x6c617669
This cannot be used because from this instruction we can only load 8 bit values.这不能使用,因为从这条指令我们只能加载 8 位值。 So I have load the 32 bit value directly from the memory.
所以我直接从内存中加载了 32 位值。 So how can I store the 32 bit value in memory and load it directly to a register using arm assembly?
那么如何将 32 位值存储在内存中并使用 arm 组件将其直接加载到寄存器中呢?
I tried this code.我试过这个代码。
.global main
main:
sub sp,sp,#4
str lr,[sp,#0]
sub sp,sp,#4
str r0,x
add sp,sp,#4
ldr lr,[sp,#0]
add sp,sp,#4
mov pc,lr
.data
x: .word 0x6c617669
But gives the following error.但给出以下错误。
test1.s: Assembler messages:
test1.s:45: Error: internal_relocation (type: OFFSET_IMM) not fixed up
You have two basic choices.您有两个基本选择。 You can load it or build up the register 8 non-zero bits at a time
您可以一次加载它或建立寄存器 8 个非零位
mov r0,#0x12000000 @ construct from 8-bit rotated immediates
orr r0,r0,#0x00340000
orr r0,r0,#0x00005600
orr r0,r0,#0x00000078
...
ldr r1,=0x12345678 @ let the assembler figure out how
...
ldr r3,myconst @ explicitly load from a nearby constant
...
myconst: .word 0x12345678
The latter two are the same, the equals trick simply asks the assembler to place the value within reach and do a pc relative load.后两者是相同的,equals 技巧只是要求汇编程序将值放置在可及范围内并执行 pc 相对加载。
Depending on your processor you may be able to use another set of instructions (ie, movw & movt).根据您的处理器,您可能可以使用另一组指令(即 movw 和 movt)。 For example, the instructions below will not work on Raspberry Pi 2 using GCC;
例如,下面的说明不适用于使用 GCC 的 Raspberry Pi 2; however, they will work on the Marvell Armada 370/XP;
然而,他们将在 Marvell Armada 370/XP 上工作; which, if I recall correctly, is a Cortex-A9
如果我没记错的话,它是 Cortex-A9
movw r1, #0x6c61
movt r1, #0x7669
... ...
r1 0x6c617669 1818326633
You can do it in another way, indirectly instead of directly:你可以用另一种方式,间接而不是直接:
.data
.balign 4
value: .word 0x6c617669
.text
.global main
main:
push {lr} /* save lr value on stack */
ldr r0, address_of_value /* r0 = &value */
ldr r0, [r0] /* r0 = *r0 = value */
pop {lr} /* load lr (R14) register from stack */
bx lr /* return from main using lr */
address_of_value: .word value
The R0 register contains the 32bit value as you can see debugging this code: R0 寄存器包含 32 位值,您可以在调试此代码时看到:
(gdb) start
Temporary breakpoint 1 at 0x103ec
Starting program: /home/pi/asm/kk
Temporary breakpoint 1, 0x000103ec in main ()
(gdb) disassemble
Dump of assembler code for function main:
0x000103e8 <+0>: push {lr} ; (str lr, [sp, #-4]!)
=> 0x000103ec <+4>: ldr r0, [pc, #8] ; 0x103fc <address_of_value>
0x000103f0 <+8>: ldr r0, [r0]
0x000103f4 <+12>: pop {lr} ; (ldr lr, [sp], #4)
0x000103f8 <+16>: bx lr
End of assembler dump.
(gdb) info registers r0
r0 0x1 1
(gdb) stepi
0x000103f0 in main ()
(gdb) stepi
0x000103f4 in main ()
(gdb) disassemble
Dump of assembler code for function main:
0x000103e8 <+0>: push {lr} ; (str lr, [sp, #-4]!)
0x000103ec <+4>: ldr r0, [pc, #8] ; 0x103fc <address_of_value>
0x000103f0 <+8>: ldr r0, [r0]
=> 0x000103f4 <+12>: pop {lr} ; (ldr lr, [sp], #4)
0x000103f8 <+16>: bx lr
End of assembler dump.
(gdb) info registers r0
r0 0x6c617669 1818326633
Regards.问候。
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