tests/utils/testapp/gen-syscall-events/gen-syscall-events.c

   1 /*
   2  * Copyright (C) 2017 Francis Deslauriers <francis.deslauriers@efficios.com>
   3  *
   4  * SPDX-License-Identifier: LGPL-2.1-only
   5  *
   6  */
   7
   8 #include <fcntl.h>
   9 #include <stdio.h>
  10 #include <sys/syscall.h>
  11 #include <unistd.h>
  12 #include <common/error.h>
  13 #include <common/align.h>
  14
  15 #include "utils.h"
  16
  17 #define MAX_LEN 16
  18
  19 /*
  20  * The LTTng system call tracing facilities can't handle page faults at the
  21  * moment. If a fault would occur while reading a syscall argument, the
  22  * tracer will report an empty string (""). Since the proper execution of the
  23  * tests which use this generator depends on some syscall string arguments being
  24  * present, this util allows us to mitigate the page-fault risk.
  25  *
  26  * This isn't a proper fix; it is simply the best we can do for now.
  27  * See bug #1261 for more context.
  28  */
  29 static
  30 void prefault_string(const char *p)
  31 {
  32         const char * const end = p + strlen(p) + 1;
  33
  34         while (p < end) {
  35                 /*
  36                  * Trigger a read attempt on *p, faulting-in the pages
  37                  * for reading.
  38                  */
  39                 asm volatile("" : : "m"(*p));
  40                 p += PAGE_SIZE;
  41         }
  42 }
  43
  44 static
  45 int open_read_close(const char *path)
  46 {
  47         int fd, ret;
  48         char buf[MAX_LEN];
  49
  50         /*
  51          * Start generating syscalls. We use syscall(2) to prevent libc from
  52          * changing the underlying syscall (e.g. calling openat(2) instead of
  53          * open(2)).
  54          */
  55         prefault_string(path);
  56         fd = syscall(SYS_openat, AT_FDCWD, path, O_RDONLY);
  57         if (fd < 0) {
  58                 PERROR_NO_LOGGER("Failed to open file with openat(): path = '%s'", path);
  59                 ret = -1;
  60                 goto error;
  61         }
  62
  63         ret = syscall(SYS_read, fd, buf, MAX_LEN);
  64         if (ret < 0) {
  65                 PERROR_NO_LOGGER("Failed to read file: path = '%s', fd = %d, length = %d",
  66                                 path, fd, MAX_LEN);
  67                 ret = -1;
  68                 goto error;
  69         }
  70
  71         ret = syscall(SYS_close, fd);
  72         if (ret == -1) {
  73                 PERROR_NO_LOGGER("Failed to close file: path = '%s', fd = %d", path, fd);
  74                 ret = -1;
  75                 goto error;
  76         }
  77
  78 error:
  79         return ret;
  80 }
  81
  82 /*
  83  * The process waits for the creation of a file passed as argument from an
  84  * external processes to execute a syscall and exiting. This is useful for tests
  85  * in combinaison with LTTng's PID tracker feature where we can trace the kernel
  86  * events generated by our test process only.
  87  */
  88 int main(int argc, char **argv)
  89 {
  90         int ret;
  91         char *start_file;
  92
  93         if (argc != 2) {
  94                 fprintf(stderr, "Error: Missing argument\n");
  95                 fprintf(stderr, "USAGE: %s PATH_WAIT_FILE\n", argv[0]);
  96                 ret = -1;
  97                 goto error;
  98         }
  99
 100         start_file = argv[1];
 101
 102         /*
 103          * Wait for the start_file to be created by an external process
 104          * (typically the test script) before executing the syscalls.
 105          */
 106         ret = wait_on_file(start_file);
 107         if (ret != 0) {
 108                 goto error;
 109         }
 110
 111         /*
 112          * Start generating syscalls. We use syscall(2) to prevent libc to change
 113          * the underlying syscall. e.g. calling openat(2) instead of open(2).
 114          */
 115         ret = open_read_close("/proc/cpuinfo");
 116         if (ret == -1) {
 117                 ret = -1;
 118                 goto error;
 119         }
 120
 121         ret = open_read_close("/proc/cmdline");
 122         if (ret == -1) {
 123                 ret = -1;
 124                 goto error;
 125         }
 126
 127 error:
 128         return ret;
 129 }