| 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 | } |