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package main
import (
"fmt"
"path/filepath"
"syscall"
"unsafe"
"golang.org/x/sys/unix"
)
const mremapMayMove = 1
// mmapBasic creates a file-backed shared mapping.
// mmap(2) allows closing the fd after mapping without invalidating the mapping.
func mmapBasic() error {
dir, cleanup, err := makeTempDir("mmap-basic")
if err != nil {
return err
}
defer cleanup()
path := filepath.Join(dir, "mmapfile.txt")
fd, err := syscall.Open(path, syscall.O_RDWR|syscall.O_CREAT|syscall.O_TRUNC, 0o644)
if err != nil {
return fmt.Errorf("open: %w", err)
}
defer syscall.Close(fd)
data := []byte("mmap shared page data")
if _, err := syscall.Write(fd, data); err != nil {
return fmt.Errorf("write: %w", err)
}
mapped, err := syscall.Mmap(fd, 0, len(data), syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_SHARED)
if err != nil {
return fmt.Errorf("mmap: %w", err)
}
defer syscall.Munmap(mapped)
copy(mapped[:4], []byte("MMAP"))
return nil
}
// mmapMsyncSync maps a file and flushes modifications via msync(2).
// Per msync(2), callers should specify exactly one of MS_SYNC or MS_ASYNC.
func mmapMsyncSync() error {
dir, cleanup, err := makeTempDir("mmap-msync-sync")
if err != nil {
return err
}
defer cleanup()
path := filepath.Join(dir, "msyncfile.txt")
fd, err := syscall.Open(path, syscall.O_RDWR|syscall.O_CREAT|syscall.O_TRUNC, 0o644)
if err != nil {
return fmt.Errorf("open: %w", err)
}
defer syscall.Close(fd)
data := []byte("msync shared page data")
if _, err := syscall.Write(fd, data); err != nil {
return fmt.Errorf("write: %w", err)
}
mapped, err := syscall.Mmap(fd, 0, len(data), syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_SHARED)
if err != nil {
return fmt.Errorf("mmap: %w", err)
}
defer syscall.Munmap(mapped)
copy(mapped[:5], []byte("MSYNC"))
_, _, errno := syscall.Syscall(syscall.SYS_MSYNC, uintptr(unsafe.Pointer(&mapped[0])), uintptr(len(mapped)), uintptr(syscall.MS_SYNC))
if errno != 0 {
return fmt.Errorf("msync: %w", errno)
}
return nil
}
// mmapMsyncInvalidFlags calls msync(2) with both MS_SYNC and MS_ASYNC.
// The kernel returns EINVAL, but enter_msync should still be captured.
func mmapMsyncInvalidFlags() error {
dir, cleanup, err := makeTempDir("mmap-msync-invalid-flags")
if err != nil {
return err
}
defer cleanup()
path := filepath.Join(dir, "msyncinvalidfile.txt")
fd, err := syscall.Open(path, syscall.O_RDWR|syscall.O_CREAT|syscall.O_TRUNC, 0o644)
if err != nil {
return fmt.Errorf("open: %w", err)
}
defer syscall.Close(fd)
data := []byte("msync invalid flags data")
if _, err := syscall.Write(fd, data); err != nil {
return fmt.Errorf("write: %w", err)
}
mapped, err := syscall.Mmap(fd, 0, len(data), syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_SHARED)
if err != nil {
return fmt.Errorf("mmap: %w", err)
}
defer syscall.Munmap(mapped)
flags := syscall.MS_SYNC | syscall.MS_ASYNC
_, _, errno := syscall.Syscall(syscall.SYS_MSYNC, uintptr(unsafe.Pointer(&mapped[0])), uintptr(len(mapped)), uintptr(flags))
if errno != syscall.EINVAL {
return fmt.Errorf("expected EINVAL from msync with both MS_SYNC|MS_ASYNC, got %v", errno)
}
return nil
}
// mmapMremapMunmap remaps an anonymous mapping and unmaps the resized region.
// It is used to validate enter_mremap/enter_munmap tracing and memory-byte
// accounting separation from I/O bytes.
func mmapMremapMunmap() error {
const pageSize = 4096
mapped, err := syscall.Mmap(-1, 0, pageSize, syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_PRIVATE|syscall.MAP_ANON)
if err != nil {
return fmt.Errorf("mmap: %w", err)
}
oldAddr := uintptr(unsafe.Pointer(&mapped[0]))
newSize := uintptr(pageSize * 2)
newAddr, _, errno := syscall.Syscall6(syscall.SYS_MREMAP, oldAddr, uintptr(len(mapped)), newSize, mremapMayMove, 0, 0)
if errno != 0 {
_ = syscall.Munmap(mapped)
return fmt.Errorf("mremap: %w", errno)
}
_, _, errno = syscall.Syscall(syscall.SYS_MUNMAP, newAddr, newSize, 0)
if errno != 0 {
return fmt.Errorf("munmap: %w", errno)
}
return nil
}
// mmapMemoryLock exercises the memory-locking cluster (mlock, mlock2, munlock,
// mlockall, munlockall — all FamilyMemory) so the integration suite captures
// their sys_enter_ tracepoints end-to-end.
//
// All locking is done on a single anonymous page (one page = small enough to
// stay well under RLIMIT_MEMLOCK for an unprivileged process). The raw syscall
// path is used throughout so the exact tracepoints fire:
// - mlock(addr, len) / munlock(addr, len) -> KindMem (captures addr+len)
// - mlock2(addr, len, 0) -> KindMem (no stdlib wrapper)
// - mlockall(MCL_CURRENT) / munlockall() -> KindNull
//
// Errors from mlock/mlock2/mlockall are tolerated best-effort: even when the
// kernel rejects the call (e.g. EPERM/ENOMEM if RLIMIT_MEMLOCK is too low), the
// sys_enter_ tracepoint has already fired, which is all this scenario needs.
// munlock/munlockall always succeed, so we clean up unconditionally.
func mmapMemoryLock() error {
const pageSize = 4096
mapped, err := syscall.Mmap(-1, 0, pageSize, syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_PRIVATE|syscall.MAP_ANON)
if err != nil {
return fmt.Errorf("mmap: %w", err)
}
defer syscall.Munmap(mapped)
addr := uintptr(unsafe.Pointer(&mapped[0]))
length := uintptr(len(mapped))
// mlock then munlock the single page (KindMem). EPERM/ENOMEM are tolerated:
// the enter tracepoint fires regardless of the eventual errno.
if _, _, errno := unix.Syscall(unix.SYS_MLOCK, addr, length, 0); errno != 0 && errno != syscall.EPERM && errno != syscall.ENOMEM {
return fmt.Errorf("mlock: %w", errno)
}
if _, _, errno := unix.Syscall(unix.SYS_MUNLOCK, addr, length, 0); errno != 0 {
return fmt.Errorf("munlock: %w", errno)
}
// mlock2(addr, len, 0) has no stdlib/x-sys wrapper; issue the raw syscall.
if _, _, errno := unix.Syscall(unix.SYS_MLOCK2, addr, length, 0); errno != 0 && errno != syscall.EPERM && errno != syscall.ENOMEM {
return fmt.Errorf("mlock2: %w", errno)
}
// Drop any lock established by mlock2 before unmapping.
if _, _, errno := unix.Syscall(unix.SYS_MUNLOCK, addr, length, 0); errno != 0 {
return fmt.Errorf("munlock after mlock2: %w", errno)
}
// mlockall(MCL_CURRENT) then munlockall() (KindNull). mlockall may fail with
// EPERM/ENOMEM for unprivileged callers when RLIMIT_MEMLOCK is too low; its
// enter tracepoint still fires. munlockall always succeeds.
if _, _, errno := unix.Syscall(unix.SYS_MLOCKALL, uintptr(unix.MCL_CURRENT), 0, 0); errno != 0 && errno != syscall.EPERM && errno != syscall.ENOMEM {
return fmt.Errorf("mlockall: %w", errno)
}
if _, _, errno := unix.Syscall(unix.SYS_MUNLOCKALL, 0, 0, 0); errno != 0 {
return fmt.Errorf("munlockall: %w", errno)
}
return nil
}
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