sendmsg

Implemented in Antinomie 0.7.0 · Syscall list

Synopsis

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

Number (x86-64)	46
ABI	64
Kernel entry point	sys_sendmsg

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

Description

Sends a message described by a msghdr (address, scatter/gather buffers and ancillary data) on 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.
-104	ECONNRESET	The connection was reset by the peer.
-32	EPIPE	The other end of a pipe or socket is closed.

Man page

sendmsg(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)	arg1.msghdr	always
↳ pointee	Entry	its iovec array, then each buffer (arg1.msghdr.iov[i].data, capped at MAX_RW_COUNT)	arg1.msghdr.iov	always
↳ pointee	Entry	destination address (sockaddr), length msg_namelen up to sizeof(sockaddr_storage)	arg1.msghdr.name	msg_name is not NULL
↳ pointee	Entry	ancillary data (cmsghdr[]), length msg_controllen	arg1.msghdr.control	always
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.