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A function pointer, also called a subroutine pointer or procedure pointer, is a pointer referencing executable code, rather than data. Dereferencing the function pointer yields the referenced function , which can be invoked and passed arguments just as in a normal function call.
This is the primary way to output data from a program by directly using a system call. The destination is identified by a numeric code. The data to be written, for instance a piece of text, is defined by a pointer and a size, given in number of bytes. write thus takes three arguments: The file code (file descriptor or fd).
The following source code is an example of an API/function hooking method which hooks by overwriting the first six bytes of a destination function with a JMP instruction to a new function. The code is compiled into a DLL file then loaded into the target process using any method of DLL injection. Using a backup of the original function one might ...
This call asks the operating system to open the specified file with the specified access rights. If the OS allows this, then it opens the file (creates an entry in the per-process file descriptor table ) and returns a handle (file descriptor, index into this table) to the user: the actual access is controlled by the OS, and the handle is a ...
How an application should make system calls to the operating system, and if the ABI specifies direct system calls rather than procedure calls to system call stubs, the system call numbers; In the case of a complete operating system ABI, the binary format of object files, program libraries, etc.
For most file systems, a program initializes access to a file in a file system using the open system call. This allocates resources associated to the file (the file descriptor), and returns a handle that the process will use to refer to that file. In some cases the open is performed by the first access.
The trampoline is a small piece of code which is constructed on the fly on the stack when the address of a nested function is taken. The trampoline sets up the static link pointer, which allows the nested function to access local variables of the enclosing function. The function pointer is then simply the address of the trampoline.
In some languages, a pointer can reference executable code, i.e., it can point to a function, method, or procedure. A function pointer will store the address of a function to be invoked. While this facility can be used to call functions dynamically, it is often a favorite technique of virus and other malicious software writers.