.

bigfile/tests/test_virtmem.c

@@ -340,6 +340,7 @@ void test_file_access_synthetic(void)
     int err;
 
     /* MUST_FAULT(code) - checks that code faults */
+    /* somewhat dup in wcfs_test.pyx              */
     sigjmp_buf    fault_jmp;
     volatile int  fault_expected = 0;
     void sigfault_handler(int sig) {

wcfs/internal/wcfs_test.pyx

@@ -23,8 +23,9 @@
 """Module wcfs_test.pyx complements wcfs_test.py with things that cannot be
 implemented in Python."""
 
-from posix.signal cimport sigaction, sigaction_t, siginfo_t, SA_SIGINFO
-from libc.signal cimport SIGBUS
+from posix.signal cimport sigaction, sigaction_t, siginfo_t, SA_SIGINFO, sigemptyset
+from libc.signal cimport SIGBUS, SIGSEGV
+from libc.setjmp cimport sigjmp_buf, sigsetjmp, siglongjmp
 from libc.stdlib cimport abort
 from libc.string cimport strlen
 from posix.unistd cimport write, sleep
@@ -32,8 +33,8 @@ from posix.types cimport off_t
 
 from cpython.exc cimport PyErr_SetFromErrno
 
-from golang cimport chan, pychan, select, panic, topyexc
-from golang cimport time
+from golang cimport chan, pychan, select, panic, topyexc, cbool
+from golang cimport sync, time
 
 # _tDB is pyx part of tDB.
 cdef class _tDB:
@@ -86,6 +87,57 @@ def read_nogil(const unsigned char[::1] mem not None) -> bytes:
     return bytes(bytearray([b]))
 
 
+# read_mustfault verifies that read-access to mem causes SIGSEGV.
+cdef sync.Mutex mustfaultMu     # one at a time as sigaction is per-process
+cdef sigjmp_buf mustfaultJmp
+cdef cbool faultExpected = False
+cdef cbool faultedOk     = False
+cdef unsigned char mustfaultG   # global var for compiler not to optimize-out p[0] access
+
+cdef void  mustfaultSighand(int sig) nogil:
+    if not faultExpected:
+        panic("unexpected fault")
+
+    # just return from sighandler to proper place
+    faultedOk = True
+    siglongjmp(mustfaultJmp, 1)
+
+cdef void _read_mustfault(const unsigned char *p) nogil except +topyexc:
+    global faultExpected, faultedOk
+
+    cdef sigaction_t act, saveact
+    act.sa_handler = mustfaultSighand
+    act.sa_flags   = 0
+
+    sigemptyset(&act.sa_mask)           # XXX err
+    sigaction(SIGSEGV, &act, &saveact)  # XXX err
+
+    faultExpected = True
+    faultedOk     = False
+
+    if sigsetjmp(mustfaultJmp, 1) == 0:
+        mustfaultG = p[0] # should pagefault -> sighandler does longjmp
+        panic("not faulted")   # XXX -> just error ?
+    else:
+        # faulted
+        if not faultedOk:
+            panic("faulted, but !faultedOk")
+
+    faultExpected = False
+    sigaction(SIGSEGV, &saveact, NULL)  # XXX err
+
+def read_mustfault(const unsigned char[::1] mem not None):
+    assert len(mem) == 1, "read_mustfault: only [1] mem is supported for now"
+    # somewhat dup of MUST_FAULT in test_virtmem.c
+
+    with nogil:
+        mustfaultMu.lock()
+        _read_mustfault(&mem[0])
+        mustfaultMu.unlock()
+
+# --------
+
+
 cdef extern from "<fcntl.h>" nogil:
     int posix_fadvise(int fd, off_t offset, off_t len, int advice);
     enum: POSIX_FADV_DONTNEED