The TurnstoneOS stores all its data at a database called TURNSTONE Operating System Database. Currently it has a one database system and several tables as config, modules, implementations, sections, symbols and relocations. You can look their definitions at utils/generatelinkerdb.c.

Compiling each c file needs several parameters to produce position indepented code with got and plt support. At boot uefi bootloader opens database and tables and links kernel entry point and dumps into the memory. You can look it at efi/main.c and cc/lib/linker.64.c.

PLT and GOT

During linking each module will have its own PLT section for locating functions. For symbol resolving PLT goes to the GOT which is at 8TiB (virtual memmory). TOS as its own GOT rows. It is not like linux got. You can look it at includes/linker.h. GOT also contains informations about each symbol. PLT has different PLT0 row for kernel and VM applications. All symbols are resolved at kernel, hence PLT0 is consist of NOP**s. However for VM applications PLT0 has a **vmcall interface and uses 0x1000 for load module.

Layout of PLT and GOT is diffrenet because both gcc, ld and linux assumes several presumptions and optimizations. Hence r15 register can be used diffrently, not for GOT.

Lazy Loading

When a function acccess performed at code section. It first jumps PLT and PLT checks if symbol resolved at GOT. If it is resolved then jumps to the address at GOT. In VM applications, if symbol is not resolved yet, code jumps into PLT0 and then a vmcall occurs. Task sends an ipc request to the tosdb manager task to load module. Tosdb Manager loads module into memory with not recursive linking and returns metadata to the VM task. VM task fills EPT and VM's page table. Then continues execution of program at VM. During page table building all sections are marked as readonly. When program tries to access the writable sections **.data, .datareloc** and **.bss** a page fault occurs. Then VM task creates clone of related section with writable properties. Hence each program will access its own writable data. You can look related code at cc/hypervisor/hypervisor_ept.64.c.

Accessing global variables at modules before a function call causes a page fault. Because PLT only handles function (procedure) calls. Hence accessing global variables needs getter/setter.