ows*_*wst 25 c assembly linker compilation binutils
我希望有人能够帮助解决我认为是链接器脚本问题的问题.
在添加对新函数的调用后,我遇到了一个奇怪的问题.没有函数调用,我的目标文件链接正确,但是,添加了新的函数调用,我得到一个未定义的引用来自另一个目标文件的符号(我已经验证它实际上是使用objdump存在).
同样奇怪的是,在函数调用存在的情况下,如果我首先使用ld -r链接所有目标文件(以提供可重定位的输出)然后使用我的链接脚本,则没有未定义的引用,但似乎链接脚本被忽略,因为输出二进制文件没有正确的入口点.
我的(交叉编译器)ld版本:
> i586-elf-ld --version
GNU ld(GNU Binutils)2.20.1.20100303
我试图证明存在"缺失"符号:
> i586-elf-ld -T link.ld -o kernel32.bin kernel_loader.o main.o stdio.o common.o gdt.o gdt.bin -y putch
Run Code Online (Sandbox Code Playgroud)main.o: reference to putch stdio.o: definition of putch main.o: In function `main': main.c:(.text+0x1f): undefined reference to `putch'
NB(当我生成此输出时,我使用gdt.bin的文件名作为nasm编译的汇编程序,它只是另一个.o文件,真的)
我可以在相应的目标文件中看到"缺失"的符号:
> i586-elf-objdump -ht stdio.o
stdio.o:文件格式elf32-i386Run Code Online (Sandbox Code Playgroud)Sections: Idx Name Size VMA LMA File off Algn 0 .text 000002f9 00000000 00000000 00000034 2**2 CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE 1 .data 0000000c 00000000 00000000 00000330 2**2 CONTENTS, ALLOC, LOAD, DATA 2 .bss 00000008 00000000 00000000 0000033c 2**2 ALLOC 3 .comment 00000012 00000000 00000000 0000033c 2**0 CONTENTS, READONLY SYMBOL TABLE: 00000000 l df *ABS* 00000000 stdio.c 00000000 l d .text 00000000 .text 00000000 l d .data 00000000 .data 00000000 l d .bss 00000000 .bss 00000000 l d .comment 00000000 .comment 00000000 g F .text 00000016 strlen 00000016 g F .text 0000005c scroll 00000008 g O .data 00000004 numrows 00000004 g O .bss 00000004 ypos 00000004 g O .data 00000004 numcols 00000004 O *COM* 00000004 screen_mem 00000000 *UND* 00000000 memcpy 00000000 *UND* 00000000 memsetw 00000072 g F .text 0000007d newline 00000000 g O .bss 00000004 xpos 000000ef g F .text 0000002e writech 00000000 g O .data 00000004 colour 0000011d g F .text 00000061 cls 0000017e g F .text 00000010 init_video 0000018e g F .text 00000133 putch 000002c1 g F .text 00000037 puts 000002f8 g F .text 00000001 set_text_colour
并且具有未解析引用的目标文件:
> i586-elf-objdump -ht main.o
Run Code Online (Sandbox Code Playgroud)main.o: file format elf32-i386 Sections: Idx Name Size VMA LMA File off Algn 0 .text 0000007f 00000000 00000000 00000034 2**2 CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE 1 .data 00000000 00000000 00000000 000000b4 2**2 CONTENTS, ALLOC, LOAD, DATA 2 .bss 00000000 00000000 00000000 000000b4 2**2 ALLOC 3 .rodata.str1.1 00000024 00000000 00000000 000000b4 2**0 CONTENTS, ALLOC, LOAD, READONLY, DATA 4 .comment 00000012 00000000 00000000 000000d8 2**0 CONTENTS, READONLY SYMBOL TABLE: 00000000 l df *ABS* 00000000 main.c 00000000 l d .text 00000000 .text 00000000 l d .data 00000000 .data 00000000 l d .bss 00000000 .bss 00000000 l d .rodata.str1.1 00000000 .rodata.str1.1 00000000 l d .comment 00000000 .comment 00000000 g F .text 0000007f main 00000000 *UND* 00000000 init_video 00000000 *UND* 00000000 gdt_install 00000000 *UND* 00000000 putch 00000000 *UND* 00000000 puts 00000018 O *COM* 00000001 gdt 00000006 O *COM* 00000001 gdtp
我的链接脚本(不确定它是否相关):
OUTPUT_FORMAT("binary")
ENTRY(start)
phys = 0x00100000;
SECTIONS
{
.text phys : AT(phys) {
code = .;
*(.text)
*(.rodata*)
. = ALIGN(4096);
}
.data . : AT(data)
{
data = .;
*(.data)
. = ALIGN(4096);
}
.bss . : AT(bss)
{
bss = .;
*(.bss)
. = ALIGN(4096);
}
end = .;
}
如果我在main.c中注释掉putch的调用,我会得到对puts的未定义引用...如果我删除了对gdt_install的调用,没有错误!
gdt_install位于C文件中,但gdt_install调用gdt.asm中定义的函数.
void gdt_install() {
/* ... */
gdt_reset();
}
[bits 32]
[section .text]
global gdt_reset
extern gdtp
gdt_reset:
lgdt [gdtp]
mov ax, 0x10 ; 0x10 offset for data segment (sizeof(struct gdt_entry) * 2)
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
mov ss, ax
jmp 0x08:gdt_reset2 ; 0x08 offset for code segment (sizeof(struct gdt_entry))
gdt_reset2:
ret ; ret back to C
为了尝试进一步诊断原因,我一直在努力重建错误.如果我将gdt_install()函数调用移动到源代码中的特定位置,我没有收到任何错误,一切正常:
int main() {
init_video();
putch('A');
puts("<- print a single char there...\n");
gdt_install();
puts("asdf\n\n");
int i;
for (i = 0; i < 15; ++i) {
if (i % 2 == 0) {
puts("even\n");
} else {
puts("odd\n");
}
}
return 0;
}
如果我将调用移到第一个puts()调用之上,我会收到puts的未定义引用!:
...
init_video();
putch('A');
gdt_install();
puts("<- print a single char there...\n");
puts("asdf\n\n");
...
i586-elf-ld -T link.ld -o kernel32.bin kernel_loader.o main.o stdio.o common.o gdt.o gdt_asm.o
main.o: In function `main':
main.c:(.text+0x2b): undefined reference to `puts'
main.c:(.text+0x37): undefined reference to `puts'
main.c:(.text+0x51): undefined reference to `puts'
main.c:(.text+0x63): undefined reference to `puts'
接下来,如果我将调用移到putch()之上,则会导致对putch的未定义引用(这是我最初调用的地方):
...
init_video();
gdt_install();
putch('A');
puts("<- print a single char there...\n");
puts("asdf\n\n");
...
main.o: In function `main':
main.c:(.text+0x1f): undefined reference to `putch'
最后,在init_video()之上,会导致对init_video的未定义引用:
...
gdt_install();
init_video();
putch('A');
puts("<- print a single char there...\n");
puts("asdf\n\n");
...
main.o: In function `main':
main.c:(.text+0x15): undefined reference to `init_video'
究竟是什么导致了这个错误？这就像gdt_install调用以某种方式"破坏"其他符号......我在任何文档中找不到任何对它的引用,但是有一些方法gdt_install函数调用可能会导致某些链接器"边界"溢出,损坏其他代码？
有没有人遇到这样的问题,或者有进一步调查的想法？我在osdev论坛上发布了:http://forum.osdev.org/viewtopic.php？ f = 1&t = 22227,但运气不好.
谢谢
编辑:
我不确定它是否相关,但是如果我在链接时省略链接脚本,之前的所有错误都会消失...(尽管如此,我的引导加载程序无法调用内核,因为它不了解elf二进制文件).
As requested, here's the main.c file before and after pre-processing and disassembled from the compiled main.o file.
before pre-processing:
#include <stdio.h>
#include <common.h>
#include <gdt.h>
int main() {
init_video();
putch('A');
gdt_install();
puts("<- print a single char there...\n");
puts("asdf\n\n");
int i;
for (i = 0; i < 15; ++i) {
if (i % 2 == 0) {
puts("even\n");
} else {
puts("odd\n");
}
}
return 0;
}
After pre-processing:
i586-elf-gcc -Wall -O -fstrength-reduce -fomit-frame-pointer -fno-inline -nostdinc -nostdlib -fsigned-char -nostartfiles -nodefaultlibs -fno-builtin -fno-stack-protector -I./include -E main.c
# 1 "main.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "main.c"
# 1 "./include/stdio.h" 1
# 1 "./include/common.h" 1
typedef unsigned short ushort;
typedef unsigned char uchar;
typedef unsigned int uint;
typedef unsigned long ulong;
typedef int size_t;
void *memcpy(void *dst, const void *src, size_t n);
void *memset(void *dst, const char val, size_t n);
void *memsetw(void *dst, const ushort val, size_t n);
void *memseti(void *dst, const int val, size_t n);
# 5 "./include/stdio.h" 2
void cls();
void writech(char c);
void putch(char c);
void puts(char *str);
void set_text_colour(uchar f, uchar b);
void init_video();
size_t strlen(char *str);
# 2 "main.c" 2
# 1 "./include/gdt.h" 1
struct gdt_entry {
ushort limit_low;
ushort base_low;
uchar base_middle;
uchar access;
uchar granularity;
uchar base_high;
} __attribute__((packed));
struct gdt_ptr {
ushort limit;
uint base;
} __attribute__((packed));
void gdt_set_gate(int n, ulong base, ulong limit, uchar access, uchar gran);
void gdt_install();
extern void gdt_reset();
# 4 "main.c" 2
int main() {
init_video();
putch('A');
gdt_install();
puts("<- print a single char there...\n");
puts("asdf\n\n");
int i;
for (i = 0; i < 15; ++i) {
if (i % 2 == 0) {
puts("even\n");
} else {
puts("odd\n");
}
}
return 0;
}
Edit, again:
Thanks to nategoose for suggesting -g3 to give nicer disassembly output:
main.o: file format elf32-i386
SYMBOL TABLE:
00000000 l df *ABS* 00000000 main.c
00000000 l d .text 00000000 .text
00000000 l d .data 00000000 .data
00000000 l d .bss 00000000 .bss
00000000 l d .rodata.str1.4 00000000 .rodata.str1.4
00000000 l d .rodata.str1.1 00000000 .rodata.str1.1
00000000 l d .stab 00000000 .stab
00000000 l d .stabstr 00000000 .stabstr
00000000 l d .comment 00000000 .comment
00000000 g F .text 0000007f main
00000000 *UND* 00000000 init_video
00000000 *UND* 00000000 putch
00000000 *UND* 00000000 gdt_install
00000000 *UND* 00000000 puts
Disassembly of section .text:
00000000 <main>:
#include <stdio.h>
#include <common.h>
#include <gdt.h>
int main() {
0: 8d 4c 24 04 lea 0x4(%esp),%ecx
4: 83 e4 f0 and $0xfffffff0,%esp
7: ff 71 fc pushl -0x4(%ecx)
a: 55 push %ebp
b: 89 e5 mov %esp,%ebp
d: 53 push %ebx
e: 51 push %ecx
init_video();
f: e8 fc ff ff ff call 10 <main+0x10>
putch('A');
14: 83 ec 0c sub $0xc,%esp
17: 6a 41 push $0x41
19: e8 fc ff ff ff call 1a <main+0x1a>
gdt_install();
1e: e8 fc ff ff ff call 1f <main+0x1f>
puts("<- print a single char there...\n");
23: c7 04 24 00 00 00 00 movl $0x0,(%esp)
2a: e8 fc ff ff ff call 2b <main+0x2b>
puts("asdf\n\n");
2f: c7 04 24 00 00 00 00 movl $0x0,(%esp)
36: e8 fc ff ff ff call 37 <main+0x37>
3b: 83 c4 10 add $0x10,%esp
int i;
for (i = 0; i < 15; ++i) {
3e: bb 00 00 00 00 mov $0x0,%ebx
if (i % 2 == 0) {
43: f6 c3 01 test $0x1,%bl
46: 75 12 jne 5a <main+0x5a>
puts("even\n");
48: 83 ec 0c sub $0xc,%esp
4b: 68 07 00 00 00 push $0x7
50: e8 fc ff ff ff call 51 <main+0x51>
55: 83 c4 10 add $0x10,%esp
58: eb 10 jmp 6a <main+0x6a>
} else {
puts("odd\n");
5a: 83 ec 0c sub $0xc,%esp
5d: 68 0d 00 00 00 push $0xd
62: e8 fc ff ff ff call 63 <main+0x63>
67: 83 c4 10 add $0x10,%esp
puts("asdf\n\n");
int i;
for (i = 0; i < 15; ++i) {
6a: 43 inc %ebx
6b: 83 fb 0f cmp $0xf,%ebx
6e: 75 d3 jne 43 <main+0x43>
puts("odd\n");
}
}
return 0;
}
70: b8 00 00 00 00 mov $0x0,%eax
75: 8d 65 f8 lea -0x8(%ebp),%esp
78: 59 pop %ecx
79: 5b pop %ebx
7a: 5d pop %ebp
7b: 8d 61 fc lea -0x4(%ecx),%esp
7e: c3 ret
And now the new output from a clean make:
$ make
nasm -f elf kernel_loader.asm -o kernel_loader.o
i586-elf-gcc -Wall -O0 -fstrength-reduce -fomit-frame-pointer -fno-inline -nostdinc -nostdlib -fsigned-char -nostartfiles -nodefaultlibs -fno-builtin -fno-stack-protector -I./include -g3 -c main.c
i586-elf-gcc -Wall -O0 -fstrength-reduce -fomit-frame-pointer -fno-inline -nostdinc -nostdlib -fsigned-char -nostartfiles -nodefaultlibs -fno-builtin -fno-stack-protector -I./include -g3 -c stdio.c
i586-elf-gcc -Wall -O0 -fstrength-reduce -fomit-frame-pointer -fno-inline -nostdinc -nostdlib -fsigned-char -nostartfiles -nodefaultlibs -fno-builtin -fno-stack-protector -I./include -g3 -c common.c
i586-elf-gcc -Wall -O0 -fstrength-reduce -fomit-frame-pointer -fno-inline -nostdinc -nostdlib -fsigned-char -nostartfiles -nodefaultlibs -fno-builtin -fno-stack-protector -I./include -g3 -c gdt.c
nasm -f elf gdt.asm -o gdt_asm.o
i586-elf-ld -T link.ld -o kernel32.bin -\( kernel_loader.o main.o stdio.o common.o gdt.o gdt_asm.o -\)
main.o: In function `main':
/cygdrive/c/programming/os/kernel/main.c:12: undefined reference to `puts'
/cygdrive/c/programming/os/kernel/main.c:14: undefined reference to `puts'
/cygdrive/c/programming/os/kernel/main.c:20: undefined reference to `puts'
/cygdrive/c/programming/os/kernel/main.c:22: undefined reference to `puts'
make: *** [kernel32.bin] Error 1
Edit 3
As requested, here's the output of nm -s on stdio.o
i586-elf-nm -s stdio.o
00000042 T cls
00000000 D colour
00000000 T init_video
U memcpy
U memsetw
0000015e T newline
00000004 D numcols
00000008 D numrows
000001e4 T putch
0000024e T puts
00000004 C screen_mem
000000b8 T scroll
00000291 T set_text_colour
00000016 T strlen
00000199 T writech
00000000 B xpos
00000004 B ypos
Edit 4 As requested, here are the entire source files. I've uploaded the files in a zip to: http://www.owenstephens.co.uk/media/files/kernel.zip Thanks for the continued interest and help, it's much appreciated!
Makefile:
NASM=nasm
GCC=i586-elf-gcc
LD=i586-elf-ld
FMT=-f elf
GFLAGS=-Wall -O0 -fstrength-reduce -fno-inline -nostdinc -nostdlib -fsigned-char -nostartfiles -nodefaultlibs -fno-builtin -fno-stack-protector -I./include -g3 -c
LFLAGS=-T link.ld
ALL=kernel_loader.o main.o stdio.o common.o gdt.o gdt_asm.o
INCLUDES=include/stdio.h include/common.h include/gdt.h
all: $(ALL) kernel32.bin
kernel_loader.o: kernel_loader.asm
$(NASM) $(FMT) $*.asm -o $@
main.o: main.c
$(GCC) $(GFLAGS) $<
stdio.o: stdio.c include/stdio.h
$(GCC) $(GFLAGS) $<
common.o: common.c include/common.h
$(GCC) $(GFLAGS) $<
gdt.o: gdt.c include/gdt.h
$(GCC) $(GFLAGS) $<
gdt_asm.o: gdt.asm
$(NASM) $(FMT) $< -o $@
kernel32.bin: $(ALL) $(INCLUDES)
$(LD) $(LFLAGS) -o $@ -\( $(ALL) -\)
clean:
rm -f $(ALL) kernel32.bin
Link script:
OUTPUT_FORMAT("binary")
ENTRY(_start)
phys = 0x00100000;
SECTIONS
{
.text phys : AT(phys) {
code = .;
*(.text)
*(.rodata*)
. = ALIGN(4096);
}
.data . : AT(data)
{
data = .;
*(.data)
. = ALIGN(4096);
}
.bss . : AT(bss)
{
bss = .;
*(.bss)
. = ALIGN(4096);
}
end = .;
}
main.c:
#include <stdio.h>
#include <common.h>
#include <gdt.h>
int main() {
gdt_install();
puts("This is a minimal example...");
return 0;
}
common.c:
#include <common.h>
void *memcpy(void *dst, const void *src, size_t n) { return (void *)0; }
void *memset(void *dst, const char val, size_t n) { return (void *)0; }
void *memsetw(void *dst, const ushort val, size_t n) { return (void *)0; }
void *memseti(void *dst, const int val, size_t n) { return (void *)0; }
stdio.c:
#include <stdio.h>
#include <common.h>
ushort *screen_mem;
int colour = 0x0F;
int xpos = 0, ypos = 0;
int numcols = 80, numrows = 25;
void init_video() {}
size_t strlen(char *str) { return 0; }
void cls() { }
inline void scroll() { }
inline void newline() { }
void writech(char c) { }
void putch(char c) { }
void puts(char *str) { }
void set_text_colour(unsigned char f, unsigned char b){ }
gdt.c:
#include <gdt.h>
struct gdt_entry gdt[3];
struct gdt_ptr gdtp;
void gdt_set_gate(int n, ulong base, ulong limit, uchar access, uchar gran) { }
void gdt_install() { }
gdt.asm:
global gdt_reset
gdt_reset:
ret
gdt_reset2:
ret
include/common.h:
#ifndef __COMMON_H
#define __COMMON_H
typedef unsigned short ushort;
typedef unsigned char uchar;
typedef unsigned int uint;
typedef unsigned long ulong;
typedef int size_t;
void *memcpy(void *dst, const void *src, size_t n);
void *memset(void *dst, const char val, size_t n);
void *memsetw(void *dst, const ushort val, size_t n);
void *memseti(void *dst, const int val, size_t n);
#endif
include/stdio.h:
#ifndef __STDIO_H
#define __STDIO_H
#include <common.h>
void cls();
void writech(char c);
void putch(char c);
void puts(char *str);
void set_text_colour(uchar f, uchar b);
void init_video();
size_t strlen(char *str);
#endif
include/gdt.h:
#ifndef __GDT_H
#define __GDT_H
#include <common.h>
struct gdt_entry {
ushort limit_low;
ushort base_low;
uchar base_middle;
uchar access;
uchar granularity;
uchar base_high;
} __attribute__((packed));
struct gdt_ptr {
ushort limit;
uint base;
} __attribute__((packed));
void gdt_set_gate(int n, ulong base, ulong limit, uchar access, uchar gran);
void gdt_install();
extern void gdt_reset();
#endif
Output of "objdump -t"ing a shared lib that includes all .o files (except the kernel_loader, hence the undefined _start symbol.
> i586-elf-objdump -t libos.so.1.0.1
libos.so.1.0.1: file format elf32-i386
SYMBOL TABLE:
08048080 l d .text 00000000 .text
08048162 l d .rodata 00000000 .rodata
08049180 l d .data 00000000 .data
0804918c l d .bss 00000000 .bss
00000000 l d .stab 00000000 .stab
00000000 l d .stabstr 00000000 .stabstr
00000000 l d .comment 00000000 .comment
00000000 l df *ABS* 00000000 main.c
00000000 l df *ABS* 00000000 stdio.c
00000000 l df *ABS* 00000000 common.c
00000000 l df *ABS* 00000000 gdt.c
00000000 l df *ABS* 00000000 gdt.asm
08048161 l .text 00000000 gdt_reset2
08049180 g O .data 00000004 colour
08048125 g F .text 00000014 memsetw
0804918c g O .bss 00000004 xpos
08049188 g O .data 00000004 numrows
08048158 g F .text 00000005 gdt_install
08048108 g F .text 0000000a memcpy
080480ee g F .text 00000005 puts
08049198 g O .bss 00000018 gdt
08049194 g O .bss 00000004 screen_mem
080480e0 g F .text 0000000e putch
08048144 g F .text 00000014 gdt_set_gate
00000000 *UND* 00000000 _start
08048160 g .text 00000000 gdt_reset
080480b4 g F .text 00000005 init_video
080480c8 g F .text 00000005 scroll
0804918c g *ABS* 00000000 __bss_start
08048112 g F .text 00000013 memset
08048080 g F .text 00000033 main
080480f3 g F .text 00000014 set_text_colour
080480cd g F .text 00000005 newline
08049190 g O .bss 00000004 ypos
080491b0 g O .bss 00000006 gdtp
0804918c g *ABS* 00000000 _edata
080491b8 g *ABS* 00000000 _end
080480c3 g F .text 00000005 cls
080480b9 g F .text 0000000a strlen
08048139 g F .text 0000000a memseti
08049184 g O .data 00000004 numcols
080480d2 g F .text 0000000e writech