accept4

Implemented in Antinomie 0.7.0 · Syscall list

Synopsis

long accept4(int fd, struct sockaddr *upeer_sockaddr, int *upeer_addrlen, int flags);

Number (x86-64)	288
ABI	common
Kernel entry point	sys_accept4

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

Description

Like accept, with flags to set non-blocking and close-on-exec on the new descriptor.

Arguments

Name	Type	Meaning
fd (arg0)	int	File descriptor to operate on.
upeer_sockaddr (arg1)	struct sockaddr *	Pointer to a buffer for the peer socket address.
upeer_addrlen (arg2)	int *	Pointer to the size of that buffer; updated by the kernel.
flags (arg3)	int	Option flags that change the behavior of the call.

Return value

On success: A new file descriptor (a non-negative number).

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
-11	EAGAIN	The call would block, or a resource is temporarily unavailable.
-9	EBADF	A file descriptor is not valid for this operation.
-24	EMFILE	The process has too many open file descriptors.

Man page

accept4(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
fd (arg0)	Entry	raw scalar word	args.0, args.fd
upeer_sockaddr (arg1)	Entry	the pointer itself, as a raw word	args.1, args.raw[1]
↳ pointee	Exit	socket address (sockaddr layout), length min(written length, capacity)	arg1.sockaddr	result is 0 or greater and the address pointer is not NULL
upeer_addrlen (arg2)	Entry	the pointer itself, as a raw word	args.2, args.raw[2]
↳ pointee	Entry	socklen_t value the program provides	arg2.socklen.capacity	the address pointer is not NULL
↳ pointee	Exit	socklen_t value the kernel wrote	arg2.socklen.output	result is 0 or greater and the address pointer is not NULL
flags (arg3)	Entry	raw scalar word; Syscall Trace also decodes it into flag names (accept group), listing unknown bits separately	args.3, args.flags

Filter fields

• Result: ret, syscall.errno, syscall.success, syscall.duration_ns.
• Argument words: args.fd (arg0), args.upeer_sockaddr (arg1), args.upeer_addrlen (arg2), args.flags (arg3); args.0 to args.5 by position.
• Structure sockaddr behind upeer_sockaddr (arg1): args.upeer_sockaddr.<member> for sa_family.
• Structure wait_status behind upeer_addrlen (arg2): args.upeer_addrlen.<member> for value.

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.