Errors

An error is a positive number in usr/vex/errno.h. A system call returns its negative in the result register, and the C library turns that into -1 with the number in errno.

The numbers are Vex numbers. They are not the Linux numbers. A program that compares an error against a literal from Linux is wrong on Vex. A C library defines each POSIX name from the __k_ name in this header. It may add numbers of its own above the kernel ones for errors that the kernel never returns. The bootstrap C library, mlibc, does so from 2001.

ISO C takes the range 101 to 103. POSIX takes 201 and up. The kernel also has -ERESTART (4095), which never reaches a program: the return path of a system call turns it into a restart or into -EINTR. The C library has its own ERESTART (2032) in the range that the kernel never returns, so the two do not clash. The mechanism is in System calls.

The string of an error comes from strerror_r() in kernel/libk/string.c. It reads the absolute value of its argument, so a caller may pass the positive number or the negated one from a system call. A number that it does not know gives unknown errnum (N), and 0 gives no error.

The values

A new error takes the next free number above the current ones. A number that a program can see must not change.

Source

• errno.h — the numbers
• vex/errno.h — the plain names for kernel code
• string.c — strerror_r and the string of each error