recvmsg

Implemented in Antinomie 0.7.0 · Syscall list

Synopsis

long recvmsg(int fd, struct user_msghdr *msg, unsigned int flags);

Number (x86-64)	47
ABI	64
Kernel entry point	sys_recvmsg

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

Description

Receives a message into a msghdr (address, buffers and ancillary data) from a socket.

Arguments

Name	Type	Meaning
fd (arg0)	int	File descriptor to operate on.
msg (arg1)	struct user_msghdr *	Pointer to a message structure.
flags (arg2)	unsigned int	Option flags that change the behavior of the call.

Return value

On success: The number of bytes transferred (see the description for what 0 means).

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.
-111	ECONNREFUSED	The connection was refused.
-4	EINTR	The call was interrupted by a signal.

Man page

recvmsg(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
msg (arg1)	Entry	the pointer itself, as a raw word	args.1, args.raw[1]
↳ pointee	Entry	structure msghdr (56 bytes), the input	arg1.msghdr	always
↳ pointee	Exit	structure msghdr, as the kernel updated it	arg1.msghdr.output	result is 0 or greater
↳ pointee	Exit	the bytes received, min(result, MAX_RW_COUNT)	arg1.msghdr.iov[i].data	result is 0 or greater
↳ pointee	Exit	sender address (sockaddr), length min(entry, written) up to sizeof(sockaddr_storage)	arg1.msghdr.name	result is 0 or greater and msg_name is not NULL
↳ pointee	Exit	ancillary data, length min(entry, written)	arg1.msghdr.control	result is 0 or greater
flags (arg2)	Entry	raw scalar word; Syscall Trace also decodes it into flag names (message group), listing unknown bits separately	args.2, args.flags

Filter fields

• Result: ret, syscall.errno, syscall.success, syscall.duration_ns.
• Argument words: args.fd (arg0), args.msg (arg1), args.flags (arg2); args.0 to args.5 by position.
• Captured strings: the args.<name> field of a path argument, and args.path, give the captured text instead of the pointer.
• Structure msghdr behind msg (arg1): args.msg.<member> for msg_control, msg_controllen, msg_flags, msg_iov, msg_iovlen, msg_name, msg_namelen.

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.