Building with GCC 10 gives the following error:
multiple definition of_nm_jansson_json_object_iter_key';
libnm/.libs/liblibnm.a(libnm_core_la-nm-json.o):/builddir/build/BUILD/NetworkManager-1.23.1/libnm-core/nm-json.c:24: first defined here /usr/bin/ld:
libnm/.libs/liblibnm.a(libnm_core_la-nm-team-utils.o):/usr/include/jansson.h:202: multiple definition of _nm_jansson_json_object_iter';
This happens because GCC 10 defaults to -fno-common and so multiple
definitions of the same global variable are not merged together.
_nm_jansson_json_* symbols are defined in nm-json.c as void pointers
and, due to the following macros in nm-json.h:
#define json_object_iter_next (*_nm_jansson_json_object_iter_next)
...
the function declaration in jansson.h:
void *json_object_iter_next(json_t *object, void *iter);
becomes a global variable as well:
void *(*_nm_jansson_json_object_iter_next)(json_t *object, void *iter);
So, the symbol is present in nm-json.o and all other object files that
include nm-json.h, and -fcommon is required. Without it, it would be
necessary to define the symbols only in one place (for example,
nm-json.c), but then static inline functions from the jannson.h header
would still refer to the original (missing) jansson functions.
For the moment, just use -fcommon.
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