1OSSL_TRACE_ENABLED(3ossl) OpenSSL OSSL_TRACE_ENABLED(3ossl)
2
6 OSSL_trace_enabled, OSSL_trace_begin, OSSL_trace_end, OSSL_TRACE_BEGIN,
7 OSSL_TRACE_END, OSSL_TRACE_CANCEL, OSSL_TRACE, OSSL_TRACE1,
8 OSSL_TRACE2, OSSL_TRACE3, OSSL_TRACE4, OSSL_TRACE5, OSSL_TRACE6,
9 OSSL_TRACE7, OSSL_TRACE8, OSSL_TRACE9, OSSL_TRACEV, OSSL_TRACE_ENABLED
10 - OpenSSL Tracing API
11
13 #include <openssl/trace.h>
14 int OSSL_trace_enabled(int category);
16 BIO *OSSL_trace_begin(int category);
18 void OSSL_trace_end(int category, BIO *channel);
19 /* trace group macros */
21 OSSL_TRACE_BEGIN(category) {
22 ...
23 if (some_error) {
24 /* Leave trace group prematurely in case of an error */
25 OSSL_TRACE_CANCEL(category);
26 goto err;
27 }
28 ...
29 } OSSL_TRACE_END(category);
30 /* one-shot trace macros */
32 OSSL_TRACE1(category, format, arg1)
33 OSSL_TRACE2(category, format, arg1, arg2)
34 ...
35 OSSL_TRACE9(category, format, arg1, ..., arg9)
36 /* check whether a trace category is enabled */
38 if (OSSL_TRACE_ENABLED(category)) {
39 ...
40 }
41
43 The functions described here are mainly interesting for those who
44 provide OpenSSL functionality, either in OpenSSL itself or in engine
45 modules or similar.
46 If tracing is enabled (see "NOTES" below), these functions are used to
48 generate free text tracing output.
49 The tracing output is divided into types which are enabled individually
51 by the application. The tracing types are described in detail in
52 "Trace types" in OSSL_trace_set_callback(3). The fallback type
53 OSSL_TRACE_CATEGORY_ALL should not be used with the functions described
54 here.
55 Tracing for a specific category is enabled if a so called trace channel
57 is attached to it. A trace channel is simply a BIO object to which the
58 application can write its trace output.
59 The application has two different ways of registering a trace channel,
61 either by directly providing a BIO object using
62 OSSL_trace_set_channel(), or by providing a callback routine using
63 OSSL_trace_set_callback(). The latter is wrapped internally by a
64 dedicated BIO object, so for the tracing code both channel types are
65 effectively indistinguishable. We call them a simple trace channel and
66 a callback trace channel, respectively.
67 To produce trace output, it is necessary to obtain a pointer to the
69 trace channel (i.e., the BIO object) using OSSL_trace_begin(), write to
70 it using arbitrary BIO output routines, and finally releases the
71 channel using OSSL_trace_end(). The OSSL_trace_begin()/OSSL_trace_end()
72 calls surrounding the trace output create a group, which acts as a
73 critical section (guarded by a mutex) to ensure that the trace output
74 of different threads does not get mixed up.
75 The tracing code normally does not call OSSL_trace_{begin,end}()
77 directly, but rather uses a set of convenience macros, see the "Macros"
78 section below.
79 Functions
81 OSSL_trace_enabled() can be used to check if tracing for the given
82 category is enabled.
83 OSSL_trace_begin() is used to starts a tracing section, and get the
85 channel for the given category in form of a BIO. This BIO can only be
86 used for output.
87 OSSL_trace_end() is used to end a tracing section.
89 Using OSSL_trace_begin() and OSSL_trace_end() to wrap tracing sections
91 is mandatory. The result of trying to produce tracing output outside
92 of such sections is undefined.
93 Macros
95 There are a number of convenience macros defined, to make tracing easy
96 and consistent.
97 OSSL_TRACE_BEGIN() and OSSL_TRACE_END() reserve the BIO "trc_out" and
99 are used as follows to wrap a trace section:
100 OSSL_TRACE_BEGIN(TLS) {
102 BIO_fprintf(trc_out, ... );
104 } OSSL_TRACE_END(TLS);
106 This will normally expand to:
108 do {
110 BIO *trc_out = OSSL_trace_begin(OSSL_TRACE_CATEGORY_TLS);
111 if (trc_out != NULL) {
112 ...
113 BIO_fprintf(trc_out, ...);
114 }
115 OSSL_trace_end(OSSL_TRACE_CATEGORY_TLS, trc_out);
116 } while (0);
117 OSSL_TRACE_CANCEL() must be used before returning from or jumping out
119 of a trace section:
120 OSSL_TRACE_BEGIN(TLS) {
122 if (some_error) {
124 OSSL_TRACE_CANCEL(TLS);
125 goto err;
126 }
127 BIO_fprintf(trc_out, ... );
128 } OSSL_TRACE_END(TLS);
130 This will normally expand to:
132 do {
134 BIO *trc_out = OSSL_trace_begin(OSSL_TRACE_CATEGORY_TLS);
135 if (trc_out != NULL) {
136 if (some_error) {
137 OSSL_trace_end(OSSL_TRACE_CATEGORY_TLS, trc_out);
138 goto err;
139 }
140 BIO_fprintf(trc_out, ... );
141 }
142 OSSL_trace_end(OSSL_TRACE_CATEGORY_TLS, trc_out);
143 } while (0);
144 OSSL_TRACE() and OSSL_TRACE1(), OSSL_TRACE2(), ... OSSL_TRACE9() are
146 so-called one-shot macros:
147 The macro call "OSSL_TRACE(category, text)", produces literal text
149 trace output.
150 The macro call "OSSL_TRACEn(category, format, arg1, ..., argn)"
152 produces printf-style trace output with n format field arguments
153 (n=1,...,9). It expands to:
154 OSSL_TRACE_BEGIN(category) {
156 BIO_printf(trc_out, format, arg1, ..., argN)
157 } OSSL_TRACE_END(category)
158 Internally, all one-shot macros are implemented using a generic
160 OSSL_TRACEV() macro, since C90 does not support variadic macros. This
161 helper macro has a rather weird synopsis and should not be used
162 directly.
163 The OSSL_TRACE_ENABLED() macro can be used to conditionally execute
165 some code only if a specific trace category is enabled. In some
166 situations this is simpler than entering a trace section using
167 OSSL_TRACE_BEGIN() and OSSL_TRACE_END(). For example, the code
168 if (OSSL_TRACE_ENABLED(TLS)) {
170 ...
171 }
172 expands to
174 if (OSSL_trace_enabled(OSSL_TRACE_CATEGORY_TLS) {
176 ...
177 }
178
180 If producing the trace output requires carrying out auxiliary
181 calculations, this auxiliary code should be placed inside a conditional
182 block which is executed only if the trace category is enabled.
183 The most natural way to do this is to place the code inside the trace
185 section itself because it already introduces such a conditional block.
186 OSSL_TRACE_BEGIN(TLS) {
188 int var = do_some_auxiliary_calculation();
189 BIO_printf(trc_out, "var = %d\n", var);
191 } OSSL_TRACE_END(TLS);
193 In some cases it is more advantageous to use a simple conditional group
195 instead of a trace section. This is the case if calculations and
196 tracing happen in different locations of the code, or if the
197 calculations are so time consuming that placing them inside a
198 (critical) trace section would create too much contention.
199 if (OSSL_TRACE_ENABLED(TLS)) {
201 int var = do_some_auxiliary_calculation();
202 OSSL_TRACE1("var = %d\n", var);
204 }
205 Note however that premature optimization of tracing code is in general
207 futile and it's better to keep the tracing code as simple as possible.
208 Because most often the limiting factor for the application's speed is
209 the time it takes to print the trace output, not to calculate it.
210 Configure Tracing
212 By default, the OpenSSL library is built with tracing disabled. To use
213 the tracing functionality documented here, it is therefore necessary to
214 configure and build OpenSSL with the 'enable-trace' option.
215 When the library is built with tracing disabled:
217 • The macro OPENSSL_NO_TRACE is defined in <openssl/opensslconf.h>.
219 • all functions are still present, but OSSL_trace_enabled() will
221 always report the categories as disabled, and all other functions
222 will do nothing.
223 • the convenience macros are defined to produce dead code. For
225 example, take this example from "Macros" section above:
226 OSSL_TRACE_BEGIN(TLS) {
228 if (condition) {
230 OSSL_TRACE_CANCEL(TLS);
231 goto err;
232 }
233 BIO_fprintf(trc_out, ... );
234 } OSSL_TRACE_END(TLS);
236 When the tracing API isn't operational, that will expand to:
238 do {
240 BIO *trc_out = NULL;
241 if (0) {
242 if (condition) {
243 ((void)0);
244 goto err;
245 }
246 BIO_fprintf(trc_out, ... );
247 }
248 } while (0);
249
251 OSSL_trace_enabled() returns 1 if tracing for the given type is
252 operational and enabled, otherwise 0.
253 OSSL_trace_begin() returns a BIO pointer if the given type is enabled,
255 otherwise NULL.
256
258 The OpenSSL Tracing API was added in OpenSSL 3.0.
259
261 Copyright 2019-2021 The OpenSSL Project Authors. All Rights Reserved.
262 Licensed under the Apache License 2.0 (the "License"). You may not use
264 this file except in compliance with the License. You can obtain a copy
265 in the file LICENSE in the source distribution or at
266 <https://www.openssl.org/source/license.html>.
2673.0.9 2023-07-27 OSSL_TRACE_ENABLED(3ossl)