A kernel can be programmed in C++, it is very similar to making a kernel in C, except that there are a few pitfalls you must take into account (runtime support, constructors, ...)
The compiler will assume that all the necessary C++ runtime support is available by default, but as we are not linking in libsupc++ into your C++ kernel, we need to add some basic functions that can be found in the cxx.cc file.
Caution: The operators new and delete cannot be used before virtual memory and pagination have been initialized.
The kernel code can't use functions from the standard libraries so we need to add some basic functions for managing memory and strings:
void itoa(char *buf, unsigned long int n, int base);
void * memset(char *dst,char src, int n);
void * memcpy(char *dst, char *src, int n);
int strlen(char *s);
int strcmp(const char *dst, char *src);
int strcpy(char *dst,const char *src);
void strcat(void *dest,const void *src);
char * strncpy(char *destString, const char *sourceString,int maxLength);
int strncmp( const char* s1, const char* s2, int c );These functions are defined in string.cc, memory.cc, itoa.cc
During the next step, we are going to use different types in our code, most of the types we are going to use unsigned types (all the bits are used to stored the integer, in signed types one bit is used to signal the sign):
typedef unsigned char u8;
typedef unsigned short u16;
typedef unsigned int u32;
typedef unsigned long long u64;
typedef signed char s8;
typedef signed short s16;
typedef signed int s32;
typedef signed long long s64;Compiling a kernel is not the same thing as compiling a linux executable, we can't use a standard library and should have no dependencies to the system.
Our Makefile will define the process to compile and link our kernel.
For x86 architecture, the followings arguments will be used for gcc/g++/ld:
# Linker
LD=ld
LDFLAG= -melf_i386 -static -L ./ -T ./arch/$(ARCH)/linker.ld
# C++ compiler
SC=g++
FLAG= $(INCDIR) -g -O2 -w -trigraphs -fno-builtin -fno-exceptions -fno-stack-protector -O0 -m32 -fno-rtti -nostdlib -nodefaultlibs
# Assembly compiler
ASM=nasm
ASMFLAG=-f elf -o
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