_start 可以是拇指功能吗? [英] Can _start be the thumb function?
问题描述
请帮助我使用 arm926ejs cpu 的 gnu 汇编器.
Help me please with gnu assembler for arm926ejs cpu.
我尝试构建一个简单的程序(test.S):
I try to build a simple program(test.S):
.global _start
_start:
mov r0, #2
bx lr
并成功构建它:
arm-none-linux-gnueabi-as -mthumb -o test.o test.S
arm-none-linux-gnueabi-ld -o test test.o
但是当我在arm目标linux环境下运行程序时，出现错误:
but when I run the program in the arm target linux environment, I get an error:
./test
Segmentation fault
我做错了什么?_start 函数可以是拇指函数吗?或者总是arm func?
What am I doing wrong? Can _start function be the thumb func? or It is always arm func?
推荐答案
你的问题是你结束了
bx lr
你希望 Linux 在那之后接管.那条确切的行一定是 Segmentation fault 的原因.
and you expect Linux to take over after that. That exact line must be the cause of Segmentation fault.
您可以尝试创建一个最小的可执行文件，然后尝试将其一分为二以查看内容并了解预期可执行文件的行为方式.
You can try to create a minimal executable then try to bisect it to see the guts and understand how an executable is expected to behave.
请参阅下面的工作示例:
See below for a working example:
.global _start
.thumb_func
_start:
mov r0, #42
mov r7, #1
svc #0
编译
arm-linux-gnueabihf-as start.s -o start.o &&arm-linux-gnueabihf-ldstart.o -o start_test
arm-linux-gnueabihf-as start.s -o start.o && arm-linux-gnueabihf-ld start.o -o start_test
然后转储看看胆量
$ arm-linux-gnueabihf-readelf -a -W start_test
$ arm-linux-gnueabihf-readelf -a -W start_test
现在你应该注意到_start
ELF Header:
Magic: 7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00
Class: ELF32
Data: 2's complement, little endian
Version: 1 (current)
OS/ABI: UNIX - System V
ABI Version: 0
Type: EXEC (Executable file)
Machine: ARM
Version: 0x1
Entry point address: 0x8055
Start of program headers: 52 (bytes into file)
Start of section headers: 160 (bytes into file)
Flags: 0x5000000, Version5 EABI
Size of this header: 52 (bytes)
Size of program headers: 32 (bytes)
Number of program headers: 1
Size of section headers: 40 (bytes)
Number of section headers: 6
Section header string table index: 3
Section Headers:
[Nr] Name Type Addr Off Size ES Flg Lk Inf Al
[ 0] NULL 00000000 000000 000000 00 0 0 0
[ 1] .text PROGBITS 00008054 000054 000006 00 AX 0 0 4
[ 2] .ARM.attributes ARM_ATTRIBUTES 00000000 00005a 000014 00 0 0 1
[ 3] .shstrtab STRTAB 00000000 00006e 000031 00 0 0 1
[ 4] .symtab SYMTAB 00000000 000190 0000e0 10 5 6 4
[ 5] .strtab STRTAB 00000000 000270 000058 00 0 0 1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings)
I (info), L (link order), G (group), T (TLS), E (exclude), x (unknown)
O (extra OS processing required) o (OS specific), p (processor specific)
There are no section groups in this file.
Program Headers:
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
LOAD 0x000000 0x00008000 0x00008000 0x0005a 0x0005a R E 0x8000
Section to Segment mapping:
Segment Sections...
00 .text
There is no dynamic section in this file.
There are no relocations in this file.
There are no unwind sections in this file.
Symbol table '.symtab' contains 14 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 00000000 0 NOTYPE LOCAL DEFAULT UND
1: 00008054 0 SECTION LOCAL DEFAULT 1
2: 00000000 0 SECTION LOCAL DEFAULT 2
3: 00000000 0 FILE LOCAL DEFAULT ABS start.o
4: 00008054 0 NOTYPE LOCAL DEFAULT 1 $t
5: 00000000 0 FILE LOCAL DEFAULT ABS
6: 0001005a 0 NOTYPE GLOBAL DEFAULT 1 _bss_end__
7: 0001005a 0 NOTYPE GLOBAL DEFAULT 1 __bss_start__
8: 0001005a 0 NOTYPE GLOBAL DEFAULT 1 __bss_end__
9: 00008055 0 FUNC GLOBAL DEFAULT 1 _start
10: 0001005a 0 NOTYPE GLOBAL DEFAULT 1 __bss_start
11: 0001005c 0 NOTYPE GLOBAL DEFAULT 1 __end__
12: 0001005a 0 NOTYPE GLOBAL DEFAULT 1 _edata
13: 0001005c 0 NOTYPE GLOBAL DEFAULT 1 _end
No version information found in this file.
Attribute Section: aeabi
File Attributes
Tag_CPU_arch: v4T
Tag_THUMB_ISA_use: Thumb-1
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