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

   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 "utils.h"
   9
  10 #include <common/align.hpp>
  11 #include <common/error.hpp>
  12
  13 #include <fcntl.h>
  14 #include <stdio.h>
  15 #include <sys/syscall.h>
  16 #include <unistd.h>
  17
  18 #define MAX_LEN 16
  19
  20 /*
  21  * The LTTng system call tracing facilities can't handle page faults at the
  22  * moment. If a fault would occur while reading a syscall argument, the
  23  * tracer will report an empty string (""). Since the proper execution of the
  24  * tests which use this generator depends on some syscall string arguments being
  25  * present, this util allows us to mitigate the page-fault risk.
  26  *
  27  * This isn't a proper fix; it is simply the best we can do for now.
  28  * See bug #1261 for more context.
  29  */
  30 static 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 += sysconf(_SC_PAGE_SIZE);
  41         }
  42 }
  43
  44 static int open_read_close(const char *path)
  45 {
  46         int fd, ret;
  47         char buf[MAX_LEN];
  48
  49         /*
  50          * Start generating syscalls. We use syscall(2) to prevent libc from
  51          * changing the underlying syscall (e.g. calling openat(2) instead of
  52          * open(2)).
  53          */
  54         prefault_string(path);
  55         fd = syscall(SYS_openat, AT_FDCWD, path, O_RDONLY);
  56         if (fd < 0) {
  57                 PERROR_NO_LOGGER("Failed to open file with openat(): path = '%s'", path);
  58                 ret = -1;
  59                 goto error;
  60         }
  61
  62         ret = syscall(SYS_read, fd, buf, MAX_LEN);
  63         if (ret < 0) {
  64                 PERROR_NO_LOGGER("Failed to read file: path = '%s', fd = %d, length = %d",
  65                                  path,
  66                                  fd,
  67                                  MAX_LEN);
  68                 ret = -1;
  69                 goto error;
  70         }
  71
  72         ret = syscall(SYS_close, fd);
  73         if (ret == -1) {
  74                 PERROR_NO_LOGGER("Failed to close file: path = '%s', fd = %d", path, fd);
  75                 ret = -1;
  76                 goto error;
  77         }
  78
  79 error:
  80         return ret;
  81 }
  82
  83 /*
  84  * The process waits for the creation of a file passed as argument from an
  85  * external processes to execute a syscall and exiting. This is useful for tests
  86  * in combinaison with LTTng's PID tracker feature where we can trace the kernel
  87  * events generated by our test process only.
  88  */
  89 int main(int argc, char **argv)
  90 {
  91         int ret;
  92         const char *start_file, *path1, *path2;
  93
  94         if (argc != 4) {
  95                 fprintf(stderr, "Error: Missing argument\n");
  96                 fprintf(stderr, "USAGE: %s PATH_WAIT_FILE PATH1_TO_OPEN PATH2_TO_OPEN\n", argv[0]);
  97                 ret = -1;
  98                 goto error;
  99         }
 100
 101         start_file = argv[1];
 102         path1 = argv[2];
 103         path2 = argv[3];
 104
 105         /*
 106          * Wait for the start_file to be created by an external process
 107          * (typically the test script) before executing the syscalls.
 108          */
 109         ret = wait_on_file(start_file);
 110         if (ret != 0) {
 111                 goto error;
 112         }
 113
 114         /*
 115          * Start generating syscalls. We use syscall(2) to prevent libc to change
 116          * the underlying syscall. e.g. calling openat(2) instead of open(2).
 117          */
 118         ret = open_read_close(path1);
 119         if (ret == -1) {
 120                 ret = -1;
 121                 goto error;
 122         }
 123
 124         ret = open_read_close(path2);
 125         if (ret == -1) {
 126                 ret = -1;
 127                 goto error;
 128         }
 129
 130 error:
 131         return ret;
 132 }