There are a handful of build warnings that are shown during make on Ubuntu 17.10 with GCC 7.2. This is a fresh box using Vagrant and the official Ubuntu box ubuntu/artful64.
1:
gcc -I. -DBUILD_GENTOOLS -o asn1-gentables \
./asn1-gentables.c \
`test -f 'asn1-parse.c' || echo './'`asn1-parse.c \
./asn1-func.c \
./gen-help.c
./asn1-gentables.c: In function ‘one_file’:
./asn1-gentables.c:283:8: warning: implicit declaration of function ‘ksba_asn_parse_file’; did you mean ‘_ksba_asn_walk_tree’? [-Wimplicit-function-declaration]
rc = ksba_asn_parse_file (fname, &tree, check_only);
^~~~~~~~~~~~~~~~~~~
_ksba_asn_walk_tree
./asn1-gentables.c:289:9: warning: implicit declaration of function ‘ksba_asn_tree_dump’; did you mean ‘_ksba_asn_node_dump’? [-Wimplicit-function-declaration]
ksba_asn_tree_dump (tree, dump_only==2? "<":NULL, fp);
^~~~~~~~~~~~~~~~~~
_ksba_asn_node_dump2:
libtool: compile: gcc -DHAVE_CONFIG_H -I. -I.. -I../gl -I../gl -g -O2 -Wall -Wcast-align -Wshadow -Wstrict-prototypes -Wpointer-arith -Wno-pointer-sign -fvisibility=hidden -MT crl.lo -MD -MP -MF .deps/crl.Tpo -c crl.c -fPIC -DPIC -o .libs/crl.o
crl.c:50:19: warning: 'oidstr_issuingDistributionPoint' defined but not used [-Wunused-const-variable=]
static const char oidstr_issuingDistributionPoint[] = "2.5.29.28";
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~3:
gcc -DHAVE_CONFIG_H -I. -I.. -g -O2 -Wall -Wcast-align -Wshadow -Wstrict-prototypes -Wpointer-arith -Wno-pointer-sign -fvisibility=hidden -MT t-dnparser.o -MD -MP -MF .deps/t-dnparser.Tpo -c -o t-dnparser.o t-dnparser.c
t-dnparser.c: In function ‘main’:
t-dnparser.c:142:7: warning: ignoring return value of ‘fread’, declared with attribute warn_unused_result [-Wunused-result]
fread (inputbuf, 1, sizeof inputbuf, stdin);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
t-dnparser.c:151:7: warning: ignoring return value of ‘fread’, declared with attribute warn_unused_result [-Wunused-result]
fread (inputbuf, 1, sizeof inputbuf, stdin);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~