我是操作系统开发的新手，我找到了一个半简单的操作系统来帮助启动，操作系统是"Test Os kernel"，我下载并使用bochs运行它，所以我决定进入下一个级别并尝试编译，实际上我使用MinGW Developer Studio 2.05，而且我的操作系统是vista而不是linux。
当我尝试编译项目时，我收到以下段错误：
kern\.\memory\gdt.c:113: error: conflicting types for 'GDT_set_descriptor'
kern\.\memory\gdt.c:85: error: previous implicit declaration of 'GDT_set_descriptor' was here
kern\.\memory\gdt.c:145: error: conflicting types for 'GDT_install'
kern\.\memory\gdt.c:93: error: previous implicit declaration of 'GDT_install' was here
kern\kernel.c: In function `_start':
kern\kernel.c:29: warning: implicit declaration of function `main'
kern\kernel.c: In function `main':
kern\kernel.c:36: warning: unused variable `cmd'
tos.exe - 4 error(s), 38 warning(s)
这里的文件包含错误：
#include "../../kernel_components/libc/types.h"
/*
1-gdtdescriptor structure : the feilds of a gdt descriptor
2-gdt itelf is an array of gdtdescriptors, it contains all the gdtdescriptors
3-gdtpointer is a structure that indicates the place of the gdt in memory, this pointer is needed by the gdt register,
*/
#define GDTSIZE 16 //only 16 segments are mapped by the GDT
/*!
* gdtDescriptor : each gdt descriptor represents a segment in memory
*/
typedef struct gdtDescriptor
{
u16 segmentLimit_0_15; //the first 16bit of the segment limit (its length)
u16 segmentBase_0_15; //the first 16bit of the segment Base (its beginning)
u8 segmentBase_16_23; //8bits in the midle for the segment base (its length)
u8 segmentType : 4; //data segment or code segment or stack segment
u8 segmentOrSystemCall :1;//to revise the name of this after you know what it does
u8 Ring:2; //ring0 is kernel segment and ring=3 for user mode segment,this used for protection
u8 presentOrSwaped:1; //to indicate if the segment is present in memory or it has been swaped to the HDD
u8 segmentLimit_16_19:4;
u8 NotUsed:2; //this 2 bits feild is not used , so just put it to 0
u8 instructionSize:1; //instructionSize=1 for 32bit instructions
u8 limitUnit:1; //0 if the limit is expressed in bytes or 1 if the limit is in pages
u8 segmentBase_24_31;
} __attribute__ ((packed)); //__attribute__((packed)) so that the compiler doesn't change this structure and optimize it
struct gdtDescriptor GDT[GDTSIZE];//the global descriptor table,is an array of gdtDescriptors (segment entries)
/*!
* the folowing are used to indicate the type of segment, we use afrendly names instead of using binary parameters
* they are used as parameters of the function GDT_set_descriptor(.....)
*/
#define segmentType_CS 0xB //the segment is a code segment
#define segmentType_DS 0x3 //to indicate that the segment being created is a data segment
#define kernelMode 0x0 //ring0, a segment used to contain kernel code
#define userMode 0x3 //ring3, used for ordinary applications that dont belong to the lernel
#define presentInMemory 0x1 //the segment is present in memory or is swapped to a backbone (a disk for exmple)
#define _32bitInstructions 0x1 //instructions in the segment are 32 bit instructions
#define _16bitInstructions 0x0
#define limitInBytes 0x0 //the limit of the segment is expressed in bytes (limit=0x100 means 0x100 bytes)
#define limitInPages 0x1 //(limit=0x100 means 0x100 pages with each page can be 4k or 4M (on intel!)
/*!
* gdtPointer : the gdt pointer is used to indicate the place of the gdt in memory
*/
typedef struct gdtPointer
{
u16 limit;
u32 base;
} __attribute__ ((packed));
u32 GDT_descriptors_number=0; //the number of descriptors in the GDT
struct gdtPointer gdtr;
/*!
* GDT_init : initialize the gdt table : insert the code and data segment and copy the gdt to a new place
*/
void GDT_init()
{
//the first GDT is null
**===============ERROR 2** GDT_set_descriptor(1,0x0,0xfffff,segmentType_CS,0x1,kernelMode,presentInMemory,_32bitInstructions,limitInPages);
GDT_set_descriptor(2,0x0,0xfffff,segmentType_DS,0x1,kernelMode,presentInMemory,_32bitInstructions,limitInPages);
//initialize the GDT pointer
gdtr.base=GDT;
gdtr.limit = sizeof(struct gdtDescriptor)*GDTSIZE;
//make this GDT the system GDT by loading it to tne gdtr regiter
GDT_install(); **===============ERROR 4**
}
/*!
* GDT_set_descriptor : set a GDT descriptor,
* u32 descriptor : witch descriptor to set (the descriptor 0 is not used),1 means the first descriptor
u8 segmentType : 4; //data segment or code segment or stack segment
u8 segmentOrSystemCall :1;//to revise the name of this after you know what it does
u8 Ring:2; //ring0 is kernel segment and ring=3 for user mode segment,this used for protection
u8 presentOrSwaped:1; //to indicate if the segment is present in memory or it has been swaped to the HDD
u8 segmentLimit_16_19:4;
u8 NotUsed:2; //this 2 bits feild is not used , so just put it to 0
u8 instructionSize:1; //instructionSize=1 for 32bit instructions
u8 limitUnit:1; //0 if the limit is expressed in bytes or 1 if the limit is in pages
u32 segmentBase : adresse of the beginnig of the segment
u32 limit :size of the descriptor, if limitUnit=limitInBytes so this limit is expressed in byte not in pages
*
*/
void GDT_set_descriptor(u32 descriptor,u32 base,u32 limit,u8 segmentType,u8 segmentOrSystemCall,u8 ring,u8 presentOrSwaped, u8 instructionSize, u8 limitUnit)
{**===============ERROR 1**
struct gdtDescriptor gd;
//set gdt base
gd.segmentBase_0_15=(base & 0xffff);
gd.segmentBase_16_23=((base>>16) & 0xff);
gd.segmentBase_24_31=((base>>24) & 0xff);
//set gdt limit
gd.segmentLimit_0_15= (limit & 0xffff);
gd.segmentLimit_16_19=((limit>>16) & 0xf);
//other descriptor bits
gd.segmentType=segmentType;
gd.segmentOrSystemCall=segmentOrSystemCall;
gd.Ring=ring;
gd.presentOrSwaped=presentOrSwaped;
gd.NotUsed=0;
gd.instructionSize=instructionSize;
gd.limitUnit=limitUnit;
//add this gd descriptor to the GDT table
GDT[descriptor]=gd;
}
/*!
* GDT_install : load the new GDT to the gdtr register, that means
*/
void GDT_install()**===============ERROR 3**
{
//we need assembly here ! to make the GDTR register points our new GDT
asm("lgdt (gdtr)");
}
/*!
* GDT_install : load the new GDT to the gdtr register, that means
*/
void GDT_load_descriptor(u32 descriptor)
{
//this function must be edited so that we can add a code descriptor or a data descriptor
//for exemple GDT_load_descriptor_CS(2) this will load the second descriptor as a CS segment ie cs<--descriptor(2)
}
4个错误我在代码中的位置进行了分配 =============== ERROR number
那么可能是什么问题？
答案 0 :(得分：2)
问题是GDT_set_descriptor的定义在引用之后发生。
如果在没有前面的定义或声明的情况下调用函数，编译器会做出某些假设（“隐式声明”） - 这些假设对应于原始C语言实现中的默认假设：返回值假定为整数，整数小于“int”的-type参数被提升为int等。在这种情况下，编译器稍后会遇到具有不同返回值和参数的函数的实际定义。这个错误基本上告诉你“我已经假设了，但现在你告诉我这个”。
易于修复。或者：
（a）反转源中函数的顺序，使得被调用函数在文件中出现的时间早于调用代码
（b）提供文件顶部附近函数的前向声明（或通常通过单独的头文件完成）。
（a）通常工作量较少，但（b）通常是一种更通用的解决方案 - 特别是如果您预计需要从多个源模块调用相应的函数，通常最容易将声明放入标题中。 / p>