如何制作裸机ARM程序并在QEMU上运行它们? [英] How to make bare metal ARM programs and run them on QEMU?
本文介绍了如何制作裸机ARM程序并在QEMU上运行它们?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我正在尝试使此教程能够按预期工作而无需成功( bl main 指令后，某些操作失败). 根据教程的命令
(qemu) xp /1dw 0xa0000018
应该导致打印33(但是我却得到0x00)
a0000018: 33
这是主调用后寄存器的内容(请参阅startup.s)
(qemu) info registers
R00=a000001c R01=a000001c R02=00000006 R03=00000000
R04=00000000 R05=00000005 R06=00000006 R07=00000007
R08=00000008 R09=00000009 R10=00000000 R11=a3fffffc
R12=00000000 R13=00000000 R14=0000003c R15=00000004
PSR=800001db N--- A und32
FPSCR: 00000000
我有以下文件
main.c
startup.s
lscript.ld
Makefile
我正在使用以下工具链
arm-2013.11-24-arm-none-eabi-i686-pc-linux-gnu
Makefile :
SRCS := main.c startup.s
LINKER_NAME := lscript.ld
ELF_NAME := program.elf
BIN_NAME := program.bin
FLASH_NAME := flash.bin
CC := arm-none-eabi
CFLAGS := -nostdlib
OBJFLAGS ?= -DS
QEMUFLAGS := -M connex -pflash $(FLASH_NAME) -nographic -serial /dev/null
# Allocate 16MB to use as a virtual flash for th qemu
# bs = blocksize -> 4KB
# count = number of block -> 4096
# totalsize = 16MB
setup:
dd if=/dev/zero of=$(FLASH_NAME) bs=4096 count=4096
# Compile srcs and write to virtual flash
all: clean setup
$(CC)-gcc $(CFLAGS) -o $(ELF_NAME) -T $(LINKER_NAME) $(SRCS)
$(CC)-objcopy -O binary $(ELF_NAME) $(BIN_NAME)
dd if=$(BIN_NAME) of=$(FLASH_NAME) bs=4096 conv=notrunc
objdump:
$(CC)-objdump $(OBJFLAGS) $(ELF_NAME)
mem-placement:
$(CC)-nm -n $(ELF_NAME)
qemu:
qemu-system-arm $(QEMUFLAGS)
clean:
rm -rf *.bin
rm -rf *.elf
main.c :
static int arr[] = { 1, 10, 4, 5, 6, 7 };
static int sum;
static const int n = sizeof(arr) / sizeof(arr[0]);
int main()
{
int i;
for (i = 0; i < n; i++){
sum += arr[i];
}
return 0;
}
启动:
.section "vectors"
reset: b _start
undef: b undef
swi: b swi
pabt: b pabt
dabt: b dabt
nop
irq: b irq
fiq: b fiq
.text
_start:
init:
@@ Copy data to RAM.
ldr r0, =flash_sdata
ldr r1, =ram_sdata
ldr r2, =data_size
@@ Handle data_size == 0
cmp r2, #0
beq init_bss
copy:
ldrb r4, [r0], #1
strb r4, [r1], #1
subs r2, r2, #1
bne copy
init_bss:
@@ Initialize .bss
ldr r0, =sbss
ldr r1, =ebss
ldr r2, =bss_size
@@ Handle bss_size == 0
cmp r2, #0
beq init_stack
mov r4, #0
zero:
strb r4, [r0], #1
subs r2, r2, #1
bne zero
init_stack:
@@ Initialize the stack pointer
ldr sp, =0xA4000000
@@ **this call dosent work as expected.. (r13/sp contains 0xA4000000)**
bl main
@@ Dosent return from main
@@ r0 should now contain 33
stop:
b stop
lscript.ld :
/*
* Linker for testing purposes
* (using 16 MB virtual flash = 0x0100_0000)
*/
MEMORY {
rom (rx) : ORIGIN = 0x00000000, LENGTH = 0x01000000
ram (rwx) : ORIGIN = 0xA0000000, LENGTH = 0x04000000
}
SECTIONS {
.text : {
* (vectors);
* (.text);
} > rom
.rodata : {
* (.rodata);
} > rom
flash_sdata = .;
ram_sdata = ORIGIN(ram);
.data : AT (flash_sdata) {
* (.data);
} > ram
ram_edata = .;
data_size = ram_edata - ram_sdata;
sbss = .;
.bss : {
* (.bss);
} > ram
ebss = .;
bss_size = ebss - sbss;
/DISCARD/ : {
*(.note*)
*(.comment)
*(.ARM*)
/*
*(.debug*)
*/
}
}
反汇编可执行文件(objdump):
program.elf: file format elf32-littlearm
Disassembly of section .text:
00000000 <reset>:
0: ea000023 b 94 <_start>
00000004 <undef>:
4: eafffffe b 4 <undef>
00000008 <swi>:
8: eafffffe b 8 <swi>
0000000c <pabt>:
c: eafffffe b c <pabt>
00000010 <dabt>:
10: eafffffe b 10 <dabt>
14: e320f000 nop {0}
00000018 <irq>:
18: eafffffe b 18 <irq>
0000001c <fiq>:
1c: eafffffe b 1c <fiq>
00000020 <main>:
20: e52db004 push {fp} ; (str fp, [sp, #-4]!)
24: e28db000 add fp, sp, #0
28: e24dd00c sub sp, sp, #12
2c: e3a03000 mov r3, #0
30: e50b3008 str r3, [fp, #-8]
34: ea00000d b 70 <main+0x50>
38: e3003000 movw r3, #0
3c: e34a3000 movt r3, #40960 ; 0xa000
40: e51b2008 ldr r2, [fp, #-8]
44: e7932102 ldr r2, [r3, r2, lsl #2]
48: e3003018 movw r3, #24
4c: e34a3000 movt r3, #40960 ; 0xa000
50: e5933000 ldr r3, [r3]
54: e0822003 add r2, r2, r3
58: e3003018 movw r3, #24
5c: e34a3000 movt r3, #40960 ; 0xa000
60: e5832000 str r2, [r3]
64: e51b3008 ldr r3, [fp, #-8]
68: e2833001 add r3, r3, #1
6c: e50b3008 str r3, [fp, #-8]
70: e3a02006 mov r2, #6
74: e51b3008 ldr r3, [fp, #-8]
78: e1530002 cmp r3, r2
7c: baffffed blt 38 <main+0x18>
80: e3a03000 mov r3, #0
84: e1a00003 mov r0, r3
88: e24bd000 sub sp, fp, #0
8c: e49db004 pop {fp} ; (ldr fp, [sp], #4)
90: e12fff1e bx lr
00000094 <_start>:
94: e59f004c ldr r0, [pc, #76] ; e8 <stop+0x4>
98: e59f104c ldr r1, [pc, #76] ; ec <stop+0x8>
9c: e59f204c ldr r2, [pc, #76] ; f0 <stop+0xc>
a0: e3520000 cmp r2, #0
a4: 0a000003 beq b8 <init_bss>
000000a8 <copy>:
a8: e4d04001 ldrb r4, [r0], #1
ac: e4c14001 strb r4, [r1], #1
b0: e2522001 subs r2, r2, #1
b4: 1afffffb bne a8 <copy>
000000b8 <init_bss>:
b8: e59f0034 ldr r0, [pc, #52] ; f4 <stop+0x10>
bc: e59f1034 ldr r1, [pc, #52] ; f8 <stop+0x14>
c0: e59f2034 ldr r2, [pc, #52] ; fc <stop+0x18>
c4: e3520000 cmp r2, #0
c8: 0a000003 beq dc <init_stack>
cc: e3a04000 mov r4, #0
000000d0 <zero>:
d0: e4c04001 strb r4, [r0], #1
d4: e2522001 subs r2, r2, #1
d8: 1afffffc bne d0 <zero>
000000dc <init_stack>:
dc: e3a0d329 mov sp, #-1543503872 ; 0xa4000000
e0: ebffffce bl 20 <main>
000000e4 <stop>:
e4: eafffffe b e4 <stop>
e8: 00000104 andeq r0, r0, r4, lsl #2
ec: a0000000 andge r0, r0, r0
f0: 00000018 andeq r0, r0, r8, lsl r0
f4: a0000018 andge r0, r0, r8, lsl r0
f8: a000001c andge r0, r0, ip, lsl r0
fc: 00000004 andeq r0, r0, r4
Disassembly of section .rodata:
00000100 <n>:
100: 00000006 andeq r0, r0, r6
Disassembly of section .data:
a0000000 <arr>:
a0000000: 00000001 andeq r0, r0, r1
a0000004: 0000000a andeq r0, r0, sl
a0000008: 00000004 andeq r0, r0, r4
a000000c: 00000005 andeq r0, r0, r5
a0000010: 00000006 andeq r0, r0, r6
a0000014: 00000007 andeq r0, r0, r7
Disassembly of section .bss:
a0000018 <sum>:
a0000018: 00000000 andeq r0, r0, r0
有人可以为我指出正确的方向，为什么这不能按照我的期望工作?
感谢亨里克
解决方案
调试！
首先，查看PC和PSR:您处于未定义指令处理程序中的Undef模式.
好的，在异常模式下，LR会告诉您异常发生的位置.在PC偏移量和首选返回地址之间精确地确定了 所指向的内容之间存在一些复杂的规则，但只要注意一下，它显然就在movw/movt对附近./p>
movw指令仅在ARMv7 ISA及更高版本中有效.简短的调查告诉我，您正在仿真的机器是一些旧的PXA255，它的CPU仅实现ARMv5 ISA.因此，将其误导为早于多年的指令就不足为奇了.
显然，默认情况下，您的编译器已配置为以ARMv7为目标(这并不罕见)，因此您需要在CFLAGS中至少添加-march=armv5te才能以适当的体系结构版本为目标. 高级"挑战将是切换到另一台更新的计算机，但这将涉及使链接程序脚本适应新的内存映射，并为新的外设重写任何与硬件有关的代码，因此我将其保留为从长远来看，一旦您熟悉了裸机代码的基础知识并遍历了硬件参考手册.
I am trying to get this tutorial to work as intended without success (Something fails after the bl main instruction). According to the tutorial the command
(qemu) xp /1dw 0xa0000018
should result in the print 33 (But i get 0x00 instead)
a0000018: 33
This is the content of the registers after the main call (see startup.s)
(qemu) info registers
R00=a000001c R01=a000001c R02=00000006 R03=00000000
R04=00000000 R05=00000005 R06=00000006 R07=00000007
R08=00000008 R09=00000009 R10=00000000 R11=a3fffffc
R12=00000000 R13=00000000 R14=0000003c R15=00000004
PSR=800001db N--- A und32
FPSCR: 00000000
I have the following files
main.c
startup.s
lscript.ld
Makefile
And I am using the following toolchain
arm-2013.11-24-arm-none-eabi-i686-pc-linux-gnu
Makefile:
SRCS := main.c startup.s
LINKER_NAME := lscript.ld
ELF_NAME := program.elf
BIN_NAME := program.bin
FLASH_NAME := flash.bin
CC := arm-none-eabi
CFLAGS := -nostdlib
OBJFLAGS ?= -DS
QEMUFLAGS := -M connex -pflash $(FLASH_NAME) -nographic -serial /dev/null
# Allocate 16MB to use as a virtual flash for th qemu
# bs = blocksize -> 4KB
# count = number of block -> 4096
# totalsize = 16MB
setup:
dd if=/dev/zero of=$(FLASH_NAME) bs=4096 count=4096
# Compile srcs and write to virtual flash
all: clean setup
$(CC)-gcc $(CFLAGS) -o $(ELF_NAME) -T $(LINKER_NAME) $(SRCS)
$(CC)-objcopy -O binary $(ELF_NAME) $(BIN_NAME)
dd if=$(BIN_NAME) of=$(FLASH_NAME) bs=4096 conv=notrunc
objdump:
$(CC)-objdump $(OBJFLAGS) $(ELF_NAME)
mem-placement:
$(CC)-nm -n $(ELF_NAME)
qemu:
qemu-system-arm $(QEMUFLAGS)
clean:
rm -rf *.bin
rm -rf *.elf
main.c:
static int arr[] = { 1, 10, 4, 5, 6, 7 };
static int sum;
static const int n = sizeof(arr) / sizeof(arr[0]);
int main()
{
int i;
for (i = 0; i < n; i++){
sum += arr[i];
}
return 0;
}
startup.s:
.section "vectors"
reset: b _start
undef: b undef
swi: b swi
pabt: b pabt
dabt: b dabt
nop
irq: b irq
fiq: b fiq
.text
_start:
init:
@@ Copy data to RAM.
ldr r0, =flash_sdata
ldr r1, =ram_sdata
ldr r2, =data_size
@@ Handle data_size == 0
cmp r2, #0
beq init_bss
copy:
ldrb r4, [r0], #1
strb r4, [r1], #1
subs r2, r2, #1
bne copy
init_bss:
@@ Initialize .bss
ldr r0, =sbss
ldr r1, =ebss
ldr r2, =bss_size
@@ Handle bss_size == 0
cmp r2, #0
beq init_stack
mov r4, #0
zero:
strb r4, [r0], #1
subs r2, r2, #1
bne zero
init_stack:
@@ Initialize the stack pointer
ldr sp, =0xA4000000
@@ **this call dosent work as expected.. (r13/sp contains 0xA4000000)**
bl main
@@ Dosent return from main
@@ r0 should now contain 33
stop:
b stop
lscript.ld:
/*
* Linker for testing purposes
* (using 16 MB virtual flash = 0x0100_0000)
*/
MEMORY {
rom (rx) : ORIGIN = 0x00000000, LENGTH = 0x01000000
ram (rwx) : ORIGIN = 0xA0000000, LENGTH = 0x04000000
}
SECTIONS {
.text : {
* (vectors);
* (.text);
} > rom
.rodata : {
* (.rodata);
} > rom
flash_sdata = .;
ram_sdata = ORIGIN(ram);
.data : AT (flash_sdata) {
* (.data);
} > ram
ram_edata = .;
data_size = ram_edata - ram_sdata;
sbss = .;
.bss : {
* (.bss);
} > ram
ebss = .;
bss_size = ebss - sbss;
/DISCARD/ : {
*(.note*)
*(.comment)
*(.ARM*)
/*
*(.debug*)
*/
}
}
Disassembly of the executable (objdump):
program.elf: file format elf32-littlearm
Disassembly of section .text:
00000000 <reset>:
0: ea000023 b 94 <_start>
00000004 <undef>:
4: eafffffe b 4 <undef>
00000008 <swi>:
8: eafffffe b 8 <swi>
0000000c <pabt>:
c: eafffffe b c <pabt>
00000010 <dabt>:
10: eafffffe b 10 <dabt>
14: e320f000 nop {0}
00000018 <irq>:
18: eafffffe b 18 <irq>
0000001c <fiq>:
1c: eafffffe b 1c <fiq>
00000020 <main>:
20: e52db004 push {fp} ; (str fp, [sp, #-4]!)
24: e28db000 add fp, sp, #0
28: e24dd00c sub sp, sp, #12
2c: e3a03000 mov r3, #0
30: e50b3008 str r3, [fp, #-8]
34: ea00000d b 70 <main+0x50>
38: e3003000 movw r3, #0
3c: e34a3000 movt r3, #40960 ; 0xa000
40: e51b2008 ldr r2, [fp, #-8]
44: e7932102 ldr r2, [r3, r2, lsl #2]
48: e3003018 movw r3, #24
4c: e34a3000 movt r3, #40960 ; 0xa000
50: e5933000 ldr r3, [r3]
54: e0822003 add r2, r2, r3
58: e3003018 movw r3, #24
5c: e34a3000 movt r3, #40960 ; 0xa000
60: e5832000 str r2, [r3]
64: e51b3008 ldr r3, [fp, #-8]
68: e2833001 add r3, r3, #1
6c: e50b3008 str r3, [fp, #-8]
70: e3a02006 mov r2, #6
74: e51b3008 ldr r3, [fp, #-8]
78: e1530002 cmp r3, r2
7c: baffffed blt 38 <main+0x18>
80: e3a03000 mov r3, #0
84: e1a00003 mov r0, r3
88: e24bd000 sub sp, fp, #0
8c: e49db004 pop {fp} ; (ldr fp, [sp], #4)
90: e12fff1e bx lr
00000094 <_start>:
94: e59f004c ldr r0, [pc, #76] ; e8 <stop+0x4>
98: e59f104c ldr r1, [pc, #76] ; ec <stop+0x8>
9c: e59f204c ldr r2, [pc, #76] ; f0 <stop+0xc>
a0: e3520000 cmp r2, #0
a4: 0a000003 beq b8 <init_bss>
000000a8 <copy>:
a8: e4d04001 ldrb r4, [r0], #1
ac: e4c14001 strb r4, [r1], #1
b0: e2522001 subs r2, r2, #1
b4: 1afffffb bne a8 <copy>
000000b8 <init_bss>:
b8: e59f0034 ldr r0, [pc, #52] ; f4 <stop+0x10>
bc: e59f1034 ldr r1, [pc, #52] ; f8 <stop+0x14>
c0: e59f2034 ldr r2, [pc, #52] ; fc <stop+0x18>
c4: e3520000 cmp r2, #0
c8: 0a000003 beq dc <init_stack>
cc: e3a04000 mov r4, #0
000000d0 <zero>:
d0: e4c04001 strb r4, [r0], #1
d4: e2522001 subs r2, r2, #1
d8: 1afffffc bne d0 <zero>
000000dc <init_stack>:
dc: e3a0d329 mov sp, #-1543503872 ; 0xa4000000
e0: ebffffce bl 20 <main>
000000e4 <stop>:
e4: eafffffe b e4 <stop>
e8: 00000104 andeq r0, r0, r4, lsl #2
ec: a0000000 andge r0, r0, r0
f0: 00000018 andeq r0, r0, r8, lsl r0
f4: a0000018 andge r0, r0, r8, lsl r0
f8: a000001c andge r0, r0, ip, lsl r0
fc: 00000004 andeq r0, r0, r4
Disassembly of section .rodata:
00000100 <n>:
100: 00000006 andeq r0, r0, r6
Disassembly of section .data:
a0000000 <arr>:
a0000000: 00000001 andeq r0, r0, r1
a0000004: 0000000a andeq r0, r0, sl
a0000008: 00000004 andeq r0, r0, r4
a000000c: 00000005 andeq r0, r0, r5
a0000010: 00000006 andeq r0, r0, r6
a0000014: 00000007 andeq r0, r0, r7
Disassembly of section .bss:
a0000018 <sum>:
a0000018: 00000000 andeq r0, r0, r0
Can someone point me in the right direction to why this isn't working according to my expectations?
Thanks Henrik
解决方案
Debugging!
First, look at the PC and PSR: You're in Undef mode, in the undefined instruction handler.
OK, in an exception mode, the LR tells you where you took the exception. There are some slightly complicated rules between the PC offset and the preferred return address determining exactly what it points at, but just eyeballing it it's clearly in the vicinity of the movw/movt pair.
The movw instruction effectively only exists in the ARMv7 ISA onwards. A brief investigation tells me the machine you're emulating is some old PXA255 thing, whose CPU only implements the ARMv5 ISA. Thus it's not surprising it faults on an instruction that it predates by many years.
Your compiler is apparently configured to target ARMv7 by default (which is not uncommon), so you need to add at least -march=armv5te to your CFLAGS to target the appropriate architecture version. The 'advanced' challenge would be to switch to a different, newer, machine, but that's going to involve adapting the linker script to a new memory map and rewriting any hardware-touching code for new peripherals, so I'd save that idea for the longer term, once you're comfortable with the basics of bare-metal code and slogging through hardware reference manuals.
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