following a different path..., I added this in the rules file
-export POSIX_CFLAGS+=$(CFLAGS) +export POSIX_CFLAGS+=$(CFLAGS) $(shell pkgconf --cflags yajl) export POSIX_CFLAGS+=$(CPPFLAGS) export POSIX_CPPFLAGS+=$(CPPFLAGS) -export POSIX_LDFLAGS+=$(LDFLAGS) +export POSIX_LDFLAGS+=$(LDFLAGS) $(shell pkgconf --libs yajl) but it ends up like this /usr/bin/gcc -D_GNU_SOURCE -D_DEFAULT_SOURCE -D_X86_64_ -DUNIX -Dlinux -g -O2 -Werror=implicit-function-declaration -ffile-prefix-map=/<<PKGBUILDDIR>>=. -fstack-protector-strong -fstack-clash-protection -Wformat -Werror=format-security -fcf-protection -I/usr/include/yajl -Wdate-time -D_FORTIFY_SOURCE=2 -g -O2 -Werror=implicit-function-declaration -ffile-prefix-map=/<<PKGBUILDDIR>>=. -fstack-protector-strong -fstack-clash-protection -Wformat -Werror=format-security -fcf-protection -I/usr/include/yajl -Wdate-time -D_FORTIFY_SOURCE=2 -O3 -g -Wall -Werror-implicit-function-declaration -mtune=generic -m64 -I. -I../O.Common -I. -I. -I.. -I../../../../include/compiler/gcc -I../../../../include/os/Linux -I../../../../include -c ../yajl_test.c ../yajl_test.c: In function ‘main’: ../yajl_test.c:209:23: error: ‘yajl_allow_json5’ undeclared (first use in this function) 209 | yajl_config(hand, yajl_allow_json5, 0); | ^~~~~~~~~~~~~~~~ ../yajl_test.c:209:23: note: each undeclared identifier is reported only once for each function it appears in the embeded version seems to provide at least this extra symbols. what about integrating this symbol in the yajl library ?