userfaultfd

Implemented in Antinomie 0.7.0 · Syscall list

Synopsis

long userfaultfd(int flags);

Number (x86-64)	323
ABI	common
Kernel entry point	sys_userfaultfd

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

Description

Creates a descriptor through which user space can handle page faults for ranges of its memory.

Arguments

Name	Type	Meaning
flags (arg0)	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
-22	EINVAL	An argument is invalid.
-1	EPERM	The operation is not permitted for this process.

Man page

userfaultfd(2) on man7.org

Captured by Antinomie

Coverage mark: Implemented. All arguments are plain values, recorded as the raw argument words at entry. There is no pointee to copy and no known gap.

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
flags (arg0)	Entry	raw scalar word; Syscall Trace also decodes it into flag names (userfaultfd group), listing unknown bits separately	args.0, args.flags

Filter fields

• Result: ret, syscall.errno, syscall.success, syscall.duration_ns.
• Argument words: args.flags (arg0); args.0 to args.5 by position.

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.