Struct nc::types::rseq_t

#[repr(C)]
pub struct rseq_t {
    pub cpu_id_start: u32,
    pub cpu_id: u32,
    pub rseq_cs: rseq_cs_union_t,
    pub flags: u32,
}

struct rseq is aligned on 4 * 8 bytes to ensure it is always contained within a single cache-line.

A single struct rseq per thread is allowed.

Fields

cpu_id_start: u32

Restartable sequences cpu_id_start field. Updated by the kernel. Read by user-space with single-copy atomicity semantics. This field should only be read by the thread which registered this data structure. Aligned on 32-bit. Always contains a value in the range of possible CPUs, although the value may not be the actual current CPU (e.g. if rseq is not initialized). This CPU number value should always be compared against the value of the cpu_id field before performing a rseq commit or returning a value read from a data structure indexed using the cpu_id_start value.

cpu_id: u32

Restartable sequences cpu_id field. Updated by the kernel. Read by user-space with single-copy atomicity semantics. This field should only be read by the thread which registered this data structure. Aligned on 32-bit. Values RSEQ_CPU_ID_UNINITIALIZED and RSEQ_CPU_ID_REGISTRATION_FAILED have a special semantic: the former means "rseq uninitialized", and latter means "rseq initialization failed". This value is meant to be read within rseq critical sections and compared with the cpu_id_start value previously read, before performing the commit instruction, or read and compared with the cpu_id_start value before returning a value loaded from a data structure indexed using the cpu_id_start value.

rseq_cs: rseq_cs_union_t

Restartable sequences rseq_cs field.

Contains NULL when no critical section is active for the current thread, or holds a pointer to the currently active struct rseq_cs.

Updated by user-space, which sets the address of the currently active rseq_cs at the beginning of assembly instruction sequence block, and set to NULL by the kernel when it restarts an assembly instruction sequence block, as well as when the kernel detects that it is preempting or delivering a signal outside of the range targeted by the rseq_cs. Also needs to be set to NULL by user-space before reclaiming memory that contains the targeted struct rseq_cs.

Read and set by the kernel. Set by user-space with single-copy atomicity semantics. This field should only be updated by the thread which registered this data structure. Aligned on 64-bit.

flags: u32

Restartable sequences flags field.

This field should only be updated by the thread which registered this data structure. Read by the kernel. Mainly used for single-stepping through rseq critical sections with debuggers.

• RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT Inhibit instruction sequence block restart on preemption for this thread.
• RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL Inhibit instruction sequence block restart on signal delivery for this thread.
• RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE Inhibit instruction sequence block restart on migration for this thread.