core: fix build on musl libc (Alpine) - stray #undef _GNU_SOURCE in lib/url.c

[Lt-Flash]

What

Fixes the OpenSIPS core failing to compile on musl libc (Alpine Linux) with a modern GCC. A single stray #undef _GNU_SOURCE in lib/url.c hides the POSIX time prototypes on musl, so the very first core object (lib/url.o) never builds.

Symptom

Building master in a stock Alpine 3.24 container (musl 1.2.x, gcc 15.2.0) dies immediately:

Compiling lib/url.c
lib/../mem/../dprint.h:204:9: error: implicit declaration of function 'ctime_r'; did you mean 'ctime'?
lib/../ut.h:1401:5:  error: implicit declaration of function 'clock_gettime'; did you mean 'lock_get'?
lib/../ut.h:1401:19: error: 'CLOCK_REALTIME' undeclared (first use in this function)
make: *** [Makefile.rules:28: lib/url.o] Error 1

With gcc 14+, -Wimplicit-function-declaration is an error by default, so this is a hard build failure, not a warning. The same tree builds fine on glibc.

Root cause

lib/url.c opens with:

#define _GNU_SOURCE
#include <stdio.h>
#include <string.h>
#undef _GNU_SOURCE      /* <-- the problem */

#include "../mem/mem.h"
#include "../ut.h"       /* pulls in <time.h>: clock_gettime, ctime_r, CLOCK_REALTIME */

The difference between the two libcs is when the feature-test macros are evaluated:

• musl re-checks the feature-test macros in every system header. Its features.h only turns on the permissive default set (_BSD_SOURCE + _XOPEN_SOURCE 700, which is what exposes clock_gettime/ctime_r) when no source macro is defined:

  #if !defined(_POSIX_SOURCE) && !defined(_POSIX_C_SOURCE) \
   && !defined(_XOPEN_SOURCE) && !defined(_GNU_SOURCE) \
   && !defined(_BSD_SOURCE) && !defined(__STRICT_ANSI__)
  #define _BSD_SOURCE 1
  #define _XOPEN_SOURCE 700
  #endif

  When <stdio.h> first includes features.h, _GNU_SOURCE is defined, so that default block is skipped and features.h latches (include guard). The following #undef _GNU_SOURCE then leaves the translation unit with no feature-test macro at all. When ut.h later includes <time.h>, features.h is guard-skipped and never re-derives the defaults, so time.h's guarded prototypes (clock_gettime, ctime_r, CLOCK_REALTIME) are all absent -> implicit declarations -> build error.

• glibc latches internal __USE_POSIX*/__USE_GNU macros at the first header inclusion. The later #undef _GNU_SOURCE does not clear those, so the prototypes stay visible and the build succeeds. That is why this has gone unnoticed.

A one-line reproducer confirms the mechanism on musl:

#define _GNU_SOURCE
#include <stdio.h>
#undef _GNU_SOURCE
#include <time.h>
int main(void){ struct timespec t; clock_gettime(CLOCK_REALTIME,&t); return 0; }
// gcc: implicit declaration of 'clock_gettime'; 'CLOCK_REALTIME' undeclared
// remove the #undef line -> compiles clean

The fix

Drop the #undef and keep _GNU_SOURCE defined for the whole translation unit (with a comment explaining why). This matches how other core sources already enable it unconditionally (io_wait.h, transformations.c), and is a no-op on glibc.

+/* _GNU_SOURCE must stay defined for the rest of this file. On musl libc
+ * the feature-test macros are re-evaluated by every system header, so
+ * undefining it here would hide the clock_gettime()/ctime_r() prototypes
+ * that ut.h and dprint.h (via <time.h>) rely on, breaking the build. */
 #define _GNU_SOURCE
 #include <stdio.h>
 #include <string.h>
-#undef _GNU_SOURCE
 
 #include "../mem/mem.h"
 #include "../ut.h"

Testing

• Alpine 3.24 / musl 1.2.x / gcc 15.2.0: make opensips fails at lib/url.o before this change; builds to completion after it. Full core binary produced, modules build and load, runtime verified.
• Debian / glibc: unchanged (the #undef was already a no-op there).

lib/url.c is the only core file that uses this #define/#undef _GNU_SOURCE bracket, so this one file is the whole fix for the core.

---

Opening as a draft for maintainer review of the approach (per-file fix here vs. defining _GNU_SOURCE tree-wide in the build).

[Lt-Flash]

Pushed a second commit: the exact same defect exists in modules/mathops.

While building the full module set in an Alpine 3.24 container (musl 1.2.x, gcc 15.2.0) with the lib/url.c fix from this PR applied, the core now compiles, but mathops fails in the same way:

Compiling mathops.c
Compiling math_funcs.c
In file included from ../../parser/../ip_addr.h:47,
                 from ../../parser/msg_parser.h:49,
                 from ../../sr_module.h:48,
                 from mathops.c:41:
../../parser/../dprint.h: In function 'dp_time':
../../parser/../dprint.h:204:9: error: implicit declaration of function 'ctime_r'; did you mean 'ctime'?
make[1]: *** [../../Makefile.rules:28: mathops.o] Error 1

Both modules/mathops/mathops.c and modules/mathops/math_funcs.c open with the same define-then-undefine pattern lib/url.c had:

#ifndef _XOPEN_SOURCE
#define _XOPEN_SOURCE 600
#define _ADDED_XOPEN
#define _GNU_SOURCE
#endif

#include <stdio.h>
#include <stdlib.h>
#include <math.h>          /* this is what the macros are for */

#ifdef _ADDED_XOPEN
#undef _ADDED_XOPEN
#undef _XOPEN_SOURCE
#undef _GNU_SOURCE         /* <-- same problem as lib/url.c */
#endif

#include "../../pvar.h"    /* ... eventually dprint.h, which needs ctime_r */

The mechanism is the one described in the PR body: musl re-evaluates the feature-test macros in every system header, and its features.h only turns on the permissive default set when no source macro is defined. By the time features.h latched, _XOPEN_SOURCE/_GNU_SOURCE were defined, so the default block was skipped; the #undef then leaves the translation unit with no feature-test macro at all, and <time.h> stops declaring ctime_r(). glibc builds both files fine.

The fix is the same as for lib/url.c — drop the #undef block and let the macros stay defined for the rest of the file. _XOPEN_SOURCE 600 together with _GNU_SOURCE is a superset of what the OpenSIPS headers need on both libcs.

Verified: with this commit, mathops.so builds clean on Alpine, and the module set that previously stopped here now gets through.

---

Separately, and not part of this PR since it is a different defect class, building the full module set on musl also turns up a plain missing-include problem: net/tcp_conn_defs.h uses get_ticks() in a static inline, and several translation units that include it never get timer.h, so they fail with

../../net/tcp_conn_defs.h:210:41: error: implicit declaration of function 'get_ticks'

Files affected in my build: net/proxy_protocol.c, modules/auth_aka/aka_av_mgm.c, modules/proto_msrp/msrp_tls.c, modules/proto_ws/ws_tcp.c. These all build on glibc, where the header apparently arrives transitively. Happy to send that as its own PR if you'd like it fixed too — say the word and I'll open one.