Editing Loader (computing) (section)

==Responsibilities==
In [[Unix]], the loader is the [[callback (computer science)|handler]] for the [[system call]] <code>execve()</code>.<ref>{{cite web |url=http://www.opengroup.org/onlinepubs/000095399/functions/exec.html |title=exec |publisher=The Open Group |work=The Open Group Base Specifications Issue 6, IEEE Std 1003.1, 2004 Edition |access-date=2008-06-23}}</ref> The Unix loader's tasks include:

# validation (permissions, memory requirements etc.);
# [[memory-mapped file|memory-mapping]] the executable object from the disk into [[main memory]];
# copying the [[command-line argument]]s into virtual memory;
# initializing [[Processor register|registers]] (e.g., the stack pointer);
# jumping to the program entry point (<code>_start</code>).

In [[Microsoft Windows]] 7 and above, the loader is the <code>LdrInitializeThunk</code> function contained in [[ntdll.dll]], which does the following:

# initialisation of structures in the DLL itself (i.e. [[critical section]]s, module lists);
# validation of executable to load;
# creation of a [[dynamic memory allocation|heap]] (via the function <code>RtlCreateHeap</code>);
# allocation of environment variable block and PATH block;
# addition of executable and NTDLL to the module list (a [[doubly-linked list]]);
# loading of [[KERNEL32.DLL]] to obtain several important functions, for instance <code>BaseThreadInitThunk</code>;
# loading of executable's imports (i.e. [[dynamic-link library|dynamic-link libraries]]) recursively (check the imports' imports, their imports and so on);
# in debug mode, raising of system breakpoint;
# initialisation of DLLs;
# garbage collection;
# calling <code>NtContinue</code> on the context parameter given to the loader function (i.e. jumping to <code>RtlUserThreadStart</code>, that will start the executable)