Tests: gen-syscall-events: generate 2 events of each type for filtering

[lttng-tools.git] / tests / utils / testapp / gen-syscall-events / gen-syscall-events.c

diff --git a/tests/utils/testapp/gen-syscall-events/gen-syscall-events.c b/tests/utils/testapp/gen-syscall-events/gen-syscall-events.c
index ead6fe3870be9b31595d9f4c55d0deed08b0f39c..1ec29139e4f5d760c56d5ba27cdab4ab374a8ae1 100644 (file)
--- a/tests/utils/testapp/gen-syscall-events/gen-syscall-events.c
+++ b/tests/utils/testapp/gen-syscall-events/gen-syscall-events.c
@@ -9,10 +9,76 @@
 #include <stdio.h>
 #include <sys/syscall.h>
 #include <unistd.h>
+#include <common/error.h>
+#include <common/align.h>
 
 #include "utils.h"
 
 #define MAX_LEN 16
+
+/*
+ * 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;
+}
+
 /*
  * The process waits for the creation of a file passed as argument from an
  * external processes to execute a syscall and exiting. This is useful for tests
@@ -21,8 +87,7 @@
  */
 int main(int argc, char **argv)
 {
-       int fd, ret;
-       char buf[MAX_LEN];
+       int ret;
        char *start_file;
 
        if (argc != 2) {
@@ -47,23 +112,14 @@ int main(int argc, char **argv)
         * Start generating syscalls. We use syscall(2) to prevent libc to change
         * the underlying syscall. e.g. calling openat(2) instead of open(2).
         */
-       fd = syscall(SYS_openat, AT_FDCWD, "/proc/cpuinfo", O_RDONLY);
-       if (fd < 0) {
-               perror("open");
-               ret = -1;
-               goto error;
-       }
-
-       ret = syscall(SYS_read, fd, buf, MAX_LEN);
-       if (ret < 0) {
-               perror("read");
+       ret = open_read_close("/proc/cpuinfo");
+       if (ret == -1) {
                ret = -1;
                goto error;
        }
 
-       ret = syscall(SYS_close, fd);
+       ret = open_read_close("/proc/cmdline");
        if (ret == -1) {
-               perror("close");
                ret = -1;
                goto error;
        }