Enum Position 

pub enum Position {
    SyscallCount(u64),
    Rcb(u64),
    Syscall {
        sysno: Sysno,
        phase: Option<SyscallPhase>,
        nth: u64,
        fd: Option<i32>,
        futex_op: Option<i32>,
    },
    Rip {
        addr: Option<u64>,
        nth: u64,
    },
    Marker {
        name: String,
        nth: u64,
    },
}

The deterministic per-thread stop point that an anchor addresses.

All variants reduce to “a predicate over this thread’s deterministic event stream plus an occurrence count,” but the two leading variants (Position::SyscallCount and Position::Rcb) are absolute counts that need no per-anchor occurrence tracking.

Variants

SyscallCount(u64)

After the thread has executed exactly this many syscalls (any syscall).

Rcb(u64)

When the thread’s RCB clock reaches this absolute value.

Syscall

The nth occurrence of a specific syscall on the thread, optionally phase-qualified and restricted to one file descriptor. The occurrence is counted per thread, over that thread’s calls that match sysno (and fd), so an anchor needs no calibration run to find a syscall count.

Two properties to know when writing one:

• What is counted is syscall entries, the same unit as Position::SyscallCount. A matching call that a signal interrupts and the kernel restarts is entered, and counted, again.
• The counters belong to the thread, like its syscall count: a new thread starts at zero, an exec keeps them, and after a non-leader exec the calling thread’s counters continue under the leader’s thread id.
• By default it fires at the prehook: an edge then orders the BEFORE thread reaching its syscall, not that syscall’s effect. The held thread is re-admitted at the next drain, so a BEFORE syscall that takes more scheduler turns than the AFTER thread needs (a write to stdout takes a checkpoint turn and a resource turn) can let the AFTER thread’s effect land first, even under the default scheduler.
• With phase posthook it fires when the syscall’s result is final: a value or an errno, EINTR included, decided before the guest resumes (https://github.com/rrnewton/hermit/issues/3929). An entry that returns an internal restart code is refused (HERMIT_HB_POSTHOOK_INTERRUPTED), because the kernel decides after that point whether it returns at all. A call that only a signal handler ends (pause, rt_sigsuspend) always returns one, so a posthook anchor on it always refuses. Occurrences are counted at entry either way, and the five syscalls that do not return on success are refused at load (syscall_never_returns_on_success).
• What a hard edge orders depends on both ends. A posthook BEFORE and a prehook AFTER order the BEFORE syscall’s completed effect before the AFTER syscall runs. A posthook AFTER holds its thread only after its own call, so that call’s effect may come before the BEFORE one’s. With a prehook BEFORE, effects may land in either order.
• A posthook BEFORE on a call that only a held thread can complete never fires. A child wait or futex wait on the held thread ends in HERMIT_HB_ANCHOR_NEVER_FIRED; a read whose only writer is held is external input to the scheduler, and the run ends at --timeout.

Fields

sysno: Sysno

The syscall number.

phase: Option<SyscallPhase>

Restrict to a phase, or match any phase when None.

nth: u64

1-based occurrence.

fd: Option<i32>

Restrict to calls whose first argument is this file descriptor.

futex_op: Option<i32>

Restrict futex to calls whose operation (the low 32 bits of the second argument, as an int) is this value.

Rip

The nth execution of the instruction at an absolute address. The address is resolved later when it comes from a CodeLocation.

Fields

addr: Option<u64>

Absolute instruction pointer, or None until resolved from a CodeLocation.

nth: u64

1-based occurrence.

Marker

A cooperative guest marker. Reserved for a future backend.

Fields

name: String

Marker name.

nth: u64

1-based occurrence.

Trait Implementations

impl Clone for Position

fn clone(&self) -> Position

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Position

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Display for Position

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for Position

impl PartialEq for Position

fn eq(&self, other: &Position) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for Position