如何使用 AVR 的 gnu 汇编器相对于 PC 跳转？
我有一个使用 avr-objcopy 反汇编的二进制文件。中断向量表如下所示：
00000000 :
; VECTOR TABLE
0: 13 c0 rjmp .+38 ; 0x28, RESET
2: b8 c1 rjmp .+880 ; 0x374, INT0
4: fd cf rjmp .-6 ; 0x0
6: fc cf rjmp .-8 ; 0x0
8: fb cf rjmp .-10 ; 0x0
a: fa cf rjmp .-12 ; 0x0
c: f9 cf rjmp .-14 ; 0x0
e: f8 cf rjmp .-16 ; 0x0
10: f7 cf rjmp .-18 ; 0x0
12: c7 c1 rjmp .+910 ; 0x3a2, TIMER1 OVF
14: f5 cf rjmp .-22 ; 0x0
16: f4 cf rjmp .-24 ; 0x0
18: f3 cf rjmp .-26 ; 0x0
1a: f2 cf rjmp .-28 ; 0x0
1c: 2b c2 rjmp .+1110 ; 0x474, ADC conversion complete
1e: f0 cf rjmp .-32 ; 0x0
20: ef cf rjmp .-34 ; 0x0
22: ee cf rjmp .-36 ; 0x0
24: ed cf rjmp .-38 ; 0x0
26: 00 00 nop
; START
28: f8 94 cli
(snip)我想通过一些修改重新组装该文件。我通过删除前两列对其进行了重新格式化，使其成为常规的汇编文件。即：
.org 0
rjmp .+38 ; 0x28, RESET
rjmp .+880 ; 0x374, INT0
(snip)但是，当我运行
$ avr-as -mmcu=atmega8 test.asm
然后反汇编生成的文件时。 （使用 objcopy -S a.out）输出如下所示：
00000000 : 0: 00 c0 rjmp .+0 ; 0x2 2: 00 c0 rjmp .+0 ; 0x4 4: 00 c0 rjmp .+0 ; 0x6 6: 00 c0 rjmp .+0 ; 0x8 8: 00 c0 rjmp .+0 ; 0xa a: 00 c0 rjmp .+0 ; 0xc c: 00 c0 rjmp .+0 ; 0xe e: 00 c0 rjmp .+0 ; 0x10 10: 00 c0 rjmp .+0 ; 0x12 12: 00 c0 rjmp .+0 ; 0x14 14: 00 c0 rjmp .+0 ; 0x16 16: 00 c0 rjmp .+0 ; 0x18 18: 00 c0 rjmp .+0 ; 0x1a 1a: 00 c0 rjmp .+0 ; 0x1c 1c: 00 c0 rjmp .+0 ; 0x1e 1e: 00 c0 rjmp .+0 ; 0x20 20: 00 c0 rjmp .+0 ; 0x22 22: 00 c0 rjmp .+0 ; 0x24 24: 00 c0 rjmp .+0 ; 0x26 26: 00 00 nop 28: f8 94 cli (snip)
那么如何让 avr-as 尊重 PC 相对跳转？
I have a binary file that I've disassembled using avr-objcopy. The interrupt vector table looks like:
00000000 :
; VECTOR TABLE
0: 13 c0 rjmp .+38 ; 0x28, RESET
2: b8 c1 rjmp .+880 ; 0x374, INT0
4: fd cf rjmp .-6 ; 0x0
6: fc cf rjmp .-8 ; 0x0
8: fb cf rjmp .-10 ; 0x0
a: fa cf rjmp .-12 ; 0x0
c: f9 cf rjmp .-14 ; 0x0
e: f8 cf rjmp .-16 ; 0x0
10: f7 cf rjmp .-18 ; 0x0
12: c7 c1 rjmp .+910 ; 0x3a2, TIMER1 OVF
14: f5 cf rjmp .-22 ; 0x0
16: f4 cf rjmp .-24 ; 0x0
18: f3 cf rjmp .-26 ; 0x0
1a: f2 cf rjmp .-28 ; 0x0
1c: 2b c2 rjmp .+1110 ; 0x474, ADC conversion complete
1e: f0 cf rjmp .-32 ; 0x0
20: ef cf rjmp .-34 ; 0x0
22: ee cf rjmp .-36 ; 0x0
24: ed cf rjmp .-38 ; 0x0
26: 00 00 nop
; START
28: f8 94 cli
(snip)I want to reassemble this file with a few modifications. I've reformatted it by removing the first 2 columns so that it is a regular assembly file. ie:
.org 0
rjmp .+38 ; 0x28, RESET
rjmp .+880 ; 0x374, INT0
(snip)However, when I run
$ avr-as -mmcu=atmega8 test.asm
and then disassemble the generated file. (using objcopy -S a.out) The output looks like:
00000000 : 0: 00 c0 rjmp .+0 ; 0x2 2: 00 c0 rjmp .+0 ; 0x4 4: 00 c0 rjmp .+0 ; 0x6 6: 00 c0 rjmp .+0 ; 0x8 8: 00 c0 rjmp .+0 ; 0xa a: 00 c0 rjmp .+0 ; 0xc c: 00 c0 rjmp .+0 ; 0xe e: 00 c0 rjmp .+0 ; 0x10 10: 00 c0 rjmp .+0 ; 0x12 12: 00 c0 rjmp .+0 ; 0x14 14: 00 c0 rjmp .+0 ; 0x16 16: 00 c0 rjmp .+0 ; 0x18 18: 00 c0 rjmp .+0 ; 0x1a 1a: 00 c0 rjmp .+0 ; 0x1c 1c: 00 c0 rjmp .+0 ; 0x1e 1e: 00 c0 rjmp .+0 ; 0x20 20: 00 c0 rjmp .+0 ; 0x22 22: 00 c0 rjmp .+0 ; 0x24 24: 00 c0 rjmp .+0 ; 0x26 26: 00 00 nop 28: f8 94 cli (snip)
So how can I get avr-as to respect the PC-relative jumps?
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我找到了答案！
我正在组装但没有链接。因此汇编器用 .+0 填充所有相对跳转/调用/分支。
为了解决这个问题，我需要创建一个名为 linker.x 的自定义链接器脚本，其中包含以下内容：
SECTIONS { . = 0x0; .text : { *(.text) } }这告诉链接器在地址 0 处启动 .text 部分。
然后我可以使用以下命令链接代码：
使用上述命令链接后 all的 .+0 已填写正确的值！
这样做的原因是因为在链接阶段之前，as/gcc 不知道二进制文件中还将包含什么。链接器将所有单独的目标文件合并为一个。因此，如果链接器阶段从未运行，则无法用绝对跳转来填充相对跳转。
AVR 的汇编器完成汇编和链接。但 gnu 汇编器更通用，因此您需要单独链接。
I found the answer!
I was assembling but not linking. So the assembler was filling in all relative jumps/calls/branches with .+0.
To fix this I needed to create a custom linker script I called linker.x which contains the following:
SECTIONS { . = 0x0; .text : { *(.text) } }This tells the linker to start the .text section at address 0.
Then I could link the code using:
After linking using the above command all of the .+0's were filled in with their correct values!
The reason for this, is because until the linking stage, as/gcc don't know what else is going to be included in the binary file. It is the linker that takes all the individual object files and combines them into one. So if the linker stage is never run, there is no way to fill in the relative jumps with absolute jumps.
AVR's assembler does the both assembling and linking. But the gnu assembler is more generic and so you need to link separately.
我假设
rjmp PC+2在 avr-as 中不起作用？这就是我在 AVR Studio 中所做的...I'm assuming that
rjmp PC+2doesnt work in avr-as ? That's how I'd do it in AVR Studio...