select

Implemented in Antinomie 0.7.0 · Syscall list

Synopsis

long select(int n, fd_set *inp, fd_set *outp, fd_set *exp, struct __kernel_old_timeval *tvp);

Number (x86-64)	23
ABI	common
Kernel entry point	sys_select

This is the raw kernel prototype from the pinned Linux 6.12.94 schema, not the libc wrapper.

Description

Waits for descriptors in three sets (read, write, exceptional) to become ready, with an optional timeout.

Arguments

Name	Type	Meaning
n (arg0)	int	Number of descriptors or items.
inp (arg1)	fd_set *	fd_set of descriptors to check for reading.
outp (arg2)	fd_set *	fd_set of descriptors to check for writing.
exp (arg3)	fd_set *	fd_set of descriptors to check for exceptional conditions.
tvp (arg4)	struct __kernel_old_timeval *	Pointer to a timeout structure.

Return value

On success: the number of ready descriptors, 0 on timeout.

In an Antinomie trace the Return column and the ret filter field show the raw kernel return value. On failure that is the negative errno, for example -2 for ENOENT, not the -1 plus errno that the libc wrapper gives. syscall.errno holds the positive errno and syscall.success is false.

Common errors

Raw return	Name	Meaning
-9	EBADF	A file descriptor is not valid for this operation.
-4	EINTR	The call was interrupted by a signal.
-22	EINVAL	An argument is invalid.

Man page

select(2) on man7.org

Captured by Antinomie

Coverage mark: Implemented. Every pointer argument has a capture rule in the pinned kernel patch and none of them records a “no decoder”, “address only” or “not observed” gap on any code path. Individual values can still be incomplete on a particular call; see the capture statuses.

Every call is recorded as an Entry record (the six argument words and the pointees copied at entry) and an Exit record (the return value and the pointees copied at exit).

Arguments

Argument	When	How	Recorded field key	Condition
n (arg0)	Entry	raw scalar word	args.0, args.n
inp (arg1)	Entry	the pointer itself, as a raw word	args.1, args.raw[1]
↳ pointee	Entry and exit	bit set of descriptors, size from n (arg0), rounded up to whole words	arg1.fdset	the pointer is not NULL; at exit when the result is 0 or greater
outp (arg2)	Entry	the pointer itself, as a raw word	args.2, args.raw[2]
↳ pointee	Entry and exit	same, for writing	arg2.fdset	the pointer is not NULL; at exit when the result is 0 or greater
exp (arg3)	Entry	the pointer itself, as a raw word	args.3, args.raw[3]
↳ pointee	Entry and exit	same, for exceptional conditions	arg3.fdset	the pointer is not NULL; at exit when the result is 0 or greater
tvp (arg4)	Entry	the pointer itself, as a raw word	args.4, args.raw[4]
↳ pointee	Entry	structure timeval	arg4.timeout	the pointer is not NULL
↳ pointee	Exit	structure timeval, the time left	arg4.timeout.observed	the pointer is not NULL

Filter fields

• Result: ret, syscall.errno, syscall.success, syscall.duration_ns.
• Argument words: args.n (arg0), args.inp (arg1), args.outp (arg2), args.exp (arg3), args.tvp (arg4); args.0 to args.5 by position.
• Structure timeval[2] behind tvp (arg4): args.tvp.<member> for tv_sec, tv_usec.

See Syscall Trace filter for the full syntax.

For what the capture statuses mean, see Capture statuses. For what is never recorded, see Known gaps.