| 1 | --- |
| 2 | id: probing-the-application-source-code |
| 3 | --- |
| 4 | |
| 5 | Once tracepoints are properly defined within a tracepoint provider, |
| 6 | they may be inserted into the user application to be instrumented |
| 7 | using the `tracepoint()` macro. Its first argument is the tracepoint |
| 8 | provider name and its second is the tracepoint name. The next, optional |
| 9 | arguments are defined by the `TP_ARGS()` part of the definition of |
| 10 | the tracepoint to use. |
| 11 | |
| 12 | As an example, let us again take the following tracepoint definition: |
| 13 | |
| 14 | ~~~ c |
| 15 | TRACEPOINT_EVENT( |
| 16 | /* tracepoint provider name */ |
| 17 | my_provider, |
| 18 | |
| 19 | /* tracepoint/event name */ |
| 20 | my_first_tracepoint, |
| 21 | |
| 22 | /* list of tracepoint arguments */ |
| 23 | TP_ARGS( |
| 24 | int, my_integer_arg, |
| 25 | char*, my_string_arg |
| 26 | ), |
| 27 | |
| 28 | /* list of fields of eventual event */ |
| 29 | TP_FIELDS( |
| 30 | ctf_string(my_string_field, my_string_arg) |
| 31 | ctf_integer(int, my_integer_field, my_integer_arg) |
| 32 | ) |
| 33 | ) |
| 34 | ~~~ |
| 35 | |
| 36 | Assuming this is part of a file named `tp.h` which defines the tracepoint |
| 37 | provider and which is included by `tp.c`, here's a complete C application |
| 38 | calling this tracepoint (multiple times): |
| 39 | |
| 40 | ~~~ c |
| 41 | #define TRACEPOINT_DEFINE |
| 42 | #include "tp.h" |
| 43 | |
| 44 | int main(int argc, char* argv[]) |
| 45 | { |
| 46 | int i; |
| 47 | |
| 48 | tracepoint(my_provider, my_first_tracepoint, 23, "Hello, World!"); |
| 49 | |
| 50 | for (i = 0; i < argc; ++i) { |
| 51 | tracepoint(my_provider, my_first_tracepoint, i, argv[i]); |
| 52 | } |
| 53 | |
| 54 | return 0; |
| 55 | } |
| 56 | ~~~ |
| 57 | |
| 58 | For each tracepoint provider, `TRACEPOINT_DEFINE` must be defined into |
| 59 | exactly one translation unit (C source file) of the user application, |
| 60 | before including the tracepoint provider header file. In other words, |
| 61 | for a given tracepoint provider, you cannot define `TRACEPOINT_DEFINE`, |
| 62 | and then include its header file in two separate C source files of |
| 63 | the same application. `TRACEPOINT_DEFINE` is discussed further in |
| 64 | [Building/linking tracepoint providers and the user application](#doc-building-tracepoint-providers-and-user-application). |
| 65 | |
| 66 | As another example, remember this definition we wrote in a previous |
| 67 | section (comments are stripped): |
| 68 | |
| 69 | ~~~ c |
| 70 | /* for struct stat */ |
| 71 | #include <sys/types.h> |
| 72 | #include <sys/stat.h> |
| 73 | #include <unistd.h> |
| 74 | |
| 75 | TRACEPOINT_EVENT( |
| 76 | my_provider, |
| 77 | my_tracepoint, |
| 78 | TP_ARGS( |
| 79 | int, my_int_arg, |
| 80 | char*, my_str_arg, |
| 81 | struct stat*, st |
| 82 | ), |
| 83 | TP_FIELDS( |
| 84 | ctf_integer(int, my_constant_field, 23 + 17) |
| 85 | ctf_integer(int, my_int_arg_field, my_int_arg) |
| 86 | ctf_integer(int, my_int_arg_field2, my_int_arg * my_int_arg) |
| 87 | ctf_integer(int, sum4_field, my_str_arg[0] + my_str_arg[1] + |
| 88 | my_str_arg[2] + my_str_arg[3]) |
| 89 | ctf_string(my_str_arg_field, my_str_arg) |
| 90 | ctf_integer_hex(off_t, size_field, st->st_size) |
| 91 | ctf_float(double, size_dbl_field, (double) st->st_size) |
| 92 | ctf_sequence_text(char, half_my_str_arg_field, my_str_arg, |
| 93 | size_t, strlen(my_str_arg) / 2) |
| 94 | ) |
| 95 | ) |
| 96 | ~~~ |
| 97 | |
| 98 | Here's an example of calling it: |
| 99 | |
| 100 | ~~~ c |
| 101 | #define TRACEPOINT_DEFINE |
| 102 | #include "tp.h" |
| 103 | |
| 104 | int main(void) |
| 105 | { |
| 106 | struct stat s; |
| 107 | |
| 108 | stat("/etc/fstab", &s); |
| 109 | |
| 110 | tracepoint(my_provider, my_tracepoint, 23, "Hello, World!", &s); |
| 111 | |
| 112 | return 0; |
| 113 | } |
| 114 | ~~~ |
| 115 | |
| 116 | When viewing the trace, assuming the file size of `/etc/fstab` is |
| 117 | 301 bytes, the event generated by the execution of this tracepoint |
| 118 | should have the following fields, in this order: |
| 119 | |
| 120 | ~~~ text |
| 121 | my_constant_field 40 |
| 122 | my_int_arg_field 23 |
| 123 | my_int_arg_field2 529 |
| 124 | sum4_field 389 |
| 125 | my_str_arg_field "Hello, World!" |
| 126 | size_field 0x12d |
| 127 | size_dbl_field 301.0 |
| 128 | half_my_str_arg_field "Hello," |
| 129 | ~~~ |