ELF loader 질문

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <elf.h>
 
#define ELF_EXEC_PAGESIZE 4096
#define PAGEMASK (~(ELF_EXEC_PAGESIZE-1))
#define EXTEND(addr) (((addr) + (ELF_EXEC_PAGESIZE-1)) & PAGEMASK)
 
static void* load_elf(char* path){
 
	printf("start load_elf\n");
 
	Elf32_Ehdr eh;
	int fd, i;
 
	if((fd=open(path, O_RDWR)) < 0) printf("open\n");
	printf("%s open ok\n", path);
	if(read(fd, &eh, sizeof(Elf32_Ehdr)) < 0) printf("read ehdr\n");
	printf("read elf header ok\n");
	if(lseek(fd, eh.e_phoff, SEEK_SET) < 0) printf("lseek\n");
	printf("seek ph ok\n");
 
// 프로그램 헤더 테이블의 엔트리들을 체크하며 PT_LOAD 해야할 경우 메모리에 로드.
	int tmp=0;
	for(i=0; i<eh.e_phnum; i++){
		Elf32_Phdr ph;
		if((tmp = read(fd, &ph, eh.e_phentsize)) < 0) printf("read phdr\n");
		printf("read program header %d bytes, type %d\n", tmp, ph.p_type);
		if(ph.p_type == PT_LOAD){
			void* s_beg = (void*)(ph.p_vaddr +0x5000 & PAGEMASK);
			void* s_end = (void*)EXTEND(ph.p_vaddr +0x5000 + ph.p_filesz);
			void* z_end = (void*)EXTEND(ph.p_vaddr +0x5000 + ph.p_memsz);
			int prot = PROT_R림EAD | PROT_WRITE | PROT_EXEC;
			int flags = MAP_FIXED | MAP_PRIVATE;
			off_t offset = ph.p_offset & PAGEMASK;
			printf("mmap start : %x, size :%x, foffset : %x\n", (unsigned int)s_beg, (unsigned int)(s_end-s_beg), (unsigned int)offset);
			void* addr = mmap(s_beg, s_end - s_beg, prot, flags, fd, offset);
			if(addr == MAP_FAILED) printf("mmap\n");
			printf("mmap ok\n");
			if(z_end > s_end){
				addr = mmap(s_end, z_end - s_end, prot, flags | MAP_ANONYMOUS, 0, 0);
				if(addr == MAP_FAILED) printf("mmap zero page\n");
			}
		}
	}
	close(fd);
	return (void*)(eh.e_entry+0x5000);
}
 
int main(int argc, char* argv[]){
 
	if(argc<2){
		printf("usage: ./load [elfname]\n");
		return 0;
	}
 
	void (*func)();
	printf("loading segments...\n");
	func = load_elf( argv[1] );
	printf("entry point : %08X\n", (unsigned int)func);
	func();	// jump to entry point.
 
	return 0;
}