+
+/*
+ * The LTTng system call tracing facilities can't handle page faults at the
+ * moment. If a fault would occur while reading a syscall argument, the
+ * tracer will report an empty string (""). Since the proper execution of the
+ * tests which use this generator depends on some syscall string arguments being
+ * present, this util allows us to mitigate the page-fault risk.
+ *
+ * This isn't a proper fix; it is simply the best we can do for now.
+ * See bug #1261 for more context.
+ */
+static
+void prefault_string(const char *p)
+{
+ const char * const end = p + strlen(p) + 1;
+
+ while (p < end) {
+ /*
+ * Trigger a read attempt on *p, faulting-in the pages
+ * for reading.
+ */
+ asm volatile("" : : "m"(*p));
+ p += PAGE_SIZE;
+ }
+}
+
+static
+int open_read_close(const char *path)
+{
+ int fd, ret;
+ char buf[MAX_LEN];
+
+ /*
+ * Start generating syscalls. We use syscall(2) to prevent libc from
+ * changing the underlying syscall (e.g. calling openat(2) instead of
+ * open(2)).
+ */
+ prefault_string(path);
+ fd = syscall(SYS_openat, AT_FDCWD, path, O_RDONLY);
+ if (fd < 0) {
+ PERROR_NO_LOGGER("Failed to open file with openat(): path = '%s'", path);
+ ret = -1;
+ goto error;
+ }
+
+ ret = syscall(SYS_read, fd, buf, MAX_LEN);
+ if (ret < 0) {
+ PERROR_NO_LOGGER("Failed to read file: path = '%s', fd = %d, length = %d",
+ path, fd, MAX_LEN);
+ ret = -1;
+ goto error;
+ }
+
+ ret = syscall(SYS_close, fd);
+ if (ret == -1) {
+ PERROR_NO_LOGGER("Failed to close file: path = '%s', fd = %d", path, fd);
+ ret = -1;
+ goto error;
+ }
+
+error:
+ return ret;
+}
+