Verbose trace strings not disabled with CURL_DISABLE_VERBOSE_STRINGS

[dfandrich]

I did this

A libcurl compiled with --disable-verbose still includes trace logging strings in its binary that are never used, bloating the binary size.

I expected the following

Trace strings should not be included in the binary. This happens because in --disable-verbose mode the macros (e.g. CURL_TRC_CF are not nulled-out but rather the functions (e.g. Curl_trc_cf_infof) that those macros call are set to empty bodies. The compiler then keeps the strings in order to pass them to the empty functions that immediately return.

It appears to me that the intent was to compile away most of the trace subsystem in the CURL_DISABLE_VERBOSE_STRINGS case, so the right fix would seem to replace those macros instead of keeping empty functions around. The trace functions aren't part of the external API and are always called through those macros so this appears safe. If there are side effects in those macros calls this will break, but I hope that nobody is using the trace macros that way.

curl/libcurl version

8.19.0-DEV

operating system

Linux

[vszakats]

59a5fd8 may be related. I noticed that
variables exclusively used in verbose output had explicit (void)var; instructions
in caller code to silence unused variable warnings, though the verbose output
implementation doesn't need them. I did not dig into it, but one explanation is
logging code that could be disabled, but isn't.

To avoid triggering unused variable warnings again (or need to fiddle with the
manual suppression at caller), macros (/function stubs) could ideally insert
(void)var; instructions for unused arguments.

[jay]

didn't we have to leave it like that because not every compiler supports vaargs

curl/lib/curl_trc.h

Lines 136 to 142 in 2eebc58

	#if defined(CURL_HAVE_C99) && !defined(CURL_DISABLE_VERBOSE_STRINGS)
	#define infof(data, ...) \
	do { \
	if(Curl_trc_is_verbose(data)) \
	Curl_infof(data, __VA_ARGS__); \
	} while(0)
	#define CURL_TRC_M(data, ...) \

[vszakats]

didn't we have to leave it like that because not every compiler supports vaargs

curl/lib/curl_trc.h

Lines 136 to 142 in 2eebc58

#if defined(CURL_HAVE_C99) && !defined(CURL_DISABLE_VERBOSE_STRINGS)
#define infof(data, ...) \
do { \
if(Curl_trc_is_verbose(data)) \
Curl_infof(data, VA_ARGS); \
} while(0)
#define CURL_TRC_M(data, ...) \

That may be it! Also ref: #12105 and #12167

[jay]

so then this?

diff --git a/lib/curl_trc.h b/lib/curl_trc.h
index ff085d6..45c8e8b 100644
--- a/lib/curl_trc.h
+++ b/lib/curl_trc.h
@@ -206,7 +206,22 @@ void Curl_trc_ws(struct Curl_easy *data,
   } while(0)
 #endif /* !CURL_DISABLE_WEBSOCKETS && !CURL_DISABLE_HTTP */
 
-#else /* CURL_HAVE_C99 */
+#elif defined(CURL_HAVE_C99) && defined(CURL_DISABLE_VERBOSE_STRINGS)
+
+#define infof(data, ...)
+#define CURL_TRC_M(data, ...)
+#define CURL_TRC_CF(data, cf, ...)
+#define CURL_TRC_WRITE(data, ...)
+#define CURL_TRC_READ(data, ...)
+#define CURL_TRC_DNS(data, ...)
+#define CURL_TRC_TIMER(data, tid, ...)
+#define CURL_TRC_FTP(data, ...)
+#define CURL_TRC_SMTP(data, ...)
+#define CURL_TRC_SSLS(data, ...)
+#define CURL_TRC_SSH(data, ...)
+#define CURL_TRC_WS(data, ...)
+
+#else
 
 #define infof          Curl_infof
 #define CURL_TRC_M     Curl_trc_multi

[vszakats]

so then this?

diff --git a/lib/curl_trc.h b/lib/curl_trc.h
index ff085d6..45c8e8b 100644
--- a/lib/curl_trc.h
+++ b/lib/curl_trc.h
@@ -206,7 +206,22 @@ void Curl_trc_ws(struct Curl_easy data,
} while(0)
#endif / !CURL_DISABLE_WEBSOCKETS && !CURL_DISABLE_HTTP */

-#else /* CURL_HAVE_C99 */
+#elif defined(CURL_HAVE_C99) && defined(CURL_DISABLE_VERBOSE_STRINGS)
+
+#define infof(data, ...)
+#define CURL_TRC_M(data, ...)
+#define CURL_TRC_CF(data, cf, ...)
+#define CURL_TRC_WRITE(data, ...)
+#define CURL_TRC_READ(data, ...)
+#define CURL_TRC_DNS(data, ...)
+#define CURL_TRC_TIMER(data, tid, ...)
+#define CURL_TRC_FTP(data, ...)
+#define CURL_TRC_SMTP(data, ...)
+#define CURL_TRC_SSLS(data, ...)
+#define CURL_TRC_SSH(data, ...)
+#define CURL_TRC_WS(data, ...)
+
+#else

#define infof Curl_infof
#define CURL_TRC_M Curl_trc_multi

Something worth trying, yes. Also, to keep avoiding unused
warnings in this case, data, cf, tid should be marked
used, mapping them to this pattern:

#define CURL_TRC_CF(data, cf, ...) \
  do {                             \
    (void)data;                    \
    (void)cf;                      \
  } while(0)

edit: This will also need adding explicit (void)var; at callers, in case var is only used in a call above in the vararg list.

[vszakats]

Size comparison (in bytes) between approaches to omit orphan strings:

unity:

1380672 curl-1-master
1330800 curl-2a-preprocessor (#20353)
1330168 curl-2b-toolchain_option (#20357)
1280280 curl-3-both

non-unity:

1364112 curl-nu-1-master
1314240 curl-nu-2a-preprocessor
1330160 curl-nu-2b-toolchain_option
1280296 curl-nu-3-both

TL;DR: both remove 50KB (4%) from the binary. Applying both at the same time doubles savings to 100KB (8%). It means the two methods are removing different things. With non-unity the difference is 16K-less unused code to begin with (and -dead_strip removing this much less).

Other dead code algos (non-apple clang/gcc or msvc) may give different results.

arm64, static libcurl, non-verbose, stripped:

curl 8.19.0-DEV (Darwin) libcurl/8.19.0-DEV OpenSSL/3.6.0 zlib/1.2.12 brotli/1.2.0 zstd/1.5.7 libidn2/2.3.8 libpsl/0.21.5 libssh2/1.11.1 nghttp2/1.68.0
Protocols: dict file ftp ftps gopher gophers http https imap imaps ipfs ipns mqtt mqtts pop3 pop3s rtsp scp sftp smb smbs smtp smtps telnet tftp ws wss
Features: alt-svc AsynchDNS brotli HSTS HTTP2 HTTPS-proxy IDN IPv6 Largefile libz NTLM PSL SSL threadsafe TLS-SRP UnixSockets zstd