手动查找elf导出表函数

char* find_module_by_name(char *name){
    FILE* fp = fopen("/proc/self/maps","r");
    char line[1024] ={0};
    char* ptr = NULL;
    if(fp){
        while (fgets(line,1024,fp)){
            if(strstr(line,name)){
                sscanf(line,"%p-%*p %*s %*s %*s %*s %*s",&ptr);
                break;
            }
        }
        fclose(fp);
    }
    return ptr;
}

void* my_dlsym( char* path,  char* name){
    char* base = find_module_by_name(path);
    Elf32_Ehdr* elf_head = (Elf32_Ehdr*)base;
    Elf32_Phdr* phead_table =(Elf32_Phdr*) (base+elf_head->e_phoff);
    struct LoadableSegment{
        size_t num=0;
        size_t max_size =10;
        Elf32_Phdr* segment[10];
    }loadable_segment;
    size_t loadable_segment_num = 0;
    Elf32_Sym* sym;
    char* shdr;
    void* result = 0;
    auto get_rel_addr = [&base,&loadable_segment](Elf32_Addr it){
        for(int i=0;i<loadable_segment.num;i++){
            if( it < loadable_segment.segment[i]->p_filesz){
                return  base+ it - (off_t)loadable_segment.segment[i]->p_vaddr + loadable_segment.segment[i]->p_offset ;
            }
        }
        return (char*)NULL;
    };

    for(int i=0;i<elf_head->e_phnum;i++){
        if(phead_table[i].p_type ==PT_LOAD){
            if(loadable_segment_num>=loadable_segment.max_size){
                continue;
            }

            loadable_segment.segment[loadable_segment.num] = phead_table+i;
            loadable_segment.num++;
        }
        else if(phead_table[i].p_type ==PT_DYNAMIC){
            Elf32_Dyn* dyn = (Elf32_Dyn*)get_rel_addr(path,phead_table[i].p_offset );
            for(int j = 0;j < phead_table[i].p_memsz/phead_table[i].p_align;j++){
                Elf32_Dyn* tmp = dyn+j;
                if(dyn[j].d_tag == DT_SYMTAB ){
                    sym =(Elf32_Sym*)get_rel_addr(dyn[j].d_un.d_ptr);
                }
                if(dyn[j].d_tag == DT_STRTAB){
                    shdr = (char*)get_rel_addr(dyn[j].d_un.d_ptr);
                }
            }
            break;
        }
    }


    for (;(char*)sym<(char*)shdr;sym++){
        char* ptr = shdr+sym->st_name;
        if( strstr(ptr ,name)){
            LOGD("sym->st_value %p",sym->st_value);
            result =(void*) get_rel_addr(sym->st_value);
            LOGD("result %p",result);
        }
    }
    return result;
}

来源：CSDN

作者：浅浅徘徊

链接：https://blog.csdn.net/qq_19683651/article/details/104049343