Como criar programas ARM bare metal e executá-los no QEMU?
Estou tentando entendertutorial funcionar como pretendido sem sucesso (algo falha após obl principal instrução). De acordo com o tutorial, o comando
(qemu) xp /1dw 0xa0000018
deve resultar na impressão 33 (mas recebo 0x00)
a0000018: 33
Este é o conteúdo dos registros após a chamada principal (consulte 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
Eu tenho os seguintes arquivos
main.c
startup.s
lscript.ld
Makefile
E eu estou usando a seguinte cadeia de ferramentas
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;
}
iniciantes:
.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*)
*/
}
}
Desmontagem do executável (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
Alguém pode me indicar a direção certa de por que isso não está funcionando de acordo com minhas expectativas?
Obrigado Henrik