memfd_create

Implemented in Antinomie 0.7.0 · Syscall list

Synopsis

long memfd_create(const char *uname_ptr, unsigned int flags);


Number (x86-64)	319
ABI	common
Kernel entry point	`sys_memfd_create`

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

Description

Creates an anonymous memory-backed file and returns its descriptor.

Arguments

Name	Type	Meaning
`uname_ptr` (arg0)	`const char *`	Pointer to a module name.
`flags` (arg1)	`unsigned 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.
`-24`	`EMFILE`	The process has too many open file descriptors.

Man page

memfd_create(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
`uname_ptr` (arg0)	Entry	the pointer itself, as a raw word	`args.0`, `args.raw[0]`
↳ pointee	Entry	NUL-terminated string, up to 250 bytes	`arg0.path`	always
`flags` (arg1)	Entry	raw scalar word; Syscall Trace also decodes it into flag names (`memfd` group), listing unknown bits separately	`args.1`, `args.flags`

Filter fields

Result: ret, syscall.errno, syscall.success, syscall.duration_ns.
Argument words: args.uname_ptr (arg0), args.flags (arg1); 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.

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.