This repo has a tiny C program that uses libpq, plus a Makefile that attempts to build the C program three times: once using standard dynamic linking to libpq, once using static linking to libpq, and once using static linking with the --whole-archive linker option.
$ make do_test_dynamic
gcc -o do_test_dynamic -Wall -Werror -I"/opt/ooce/pgsql-13/include" do_test.c -L"/opt/ooce/pgsql-13/lib/amd64" -Wl,-R"/opt/ooce/pgsql-13/lib/amd64" -lpq
$ file do_test_dynamic
do_test_dynamic: ELF 64-bit LSB executable AMD64 Version 1, dynamically linked, not stripped, no debugging information available
$ ldd do_test_dynamic
libpq.so.5 => /opt/ooce/pgsql-13/lib/amd64/libpq.so.5
libc.so.1 => /lib/64/libc.so.1
libssl.so.1.1 => /lib/64/libssl.so.1.1
libcrypto.so.1.1 => /lib/64/libcrypto.so.1.1
libnsl.so.1 => /lib/64/libnsl.so.1
libsocket.so.1 => /lib/64/libsocket.so.1
libm.so.2 => /lib/64/libm.so.2
libz.so => /lib/64/libz.so
libmp.so.2 => /lib/64/libmp.so.2
libmd.so.1 => /lib/64/libmd.so.1
$ ./do_test_dynamic
PQlibVersion=130000
$
After PostgreSQL 12, this requires linking to libpgcommon and libpgport as well.
$ make do_test_static
gcc -o do_test_static -Wall -Werror -I"/opt/ooce/pgsql-13/include" do_test.c -L"/opt/ooce/pgsql-13/lib/amd64" -Wl,-Bstatic -lpq -lpgcommon -lpgport -Wl,-Bdynamic -lssl -lcrypto -lsocket
$ file do_test_static
do_test_static: ELF 64-bit LSB executable AMD64 Version 1, dynamically linked, not stripped, no debugging information available
$ ldd do_test_static
libssl.so.1.1 => /lib/64/libssl.so.1.1
libcrypto.so.1.1 => /lib/64/libcrypto.so.1.1
libsocket.so.1 => /lib/64/libsocket.so.1
libc.so.1 => /lib/64/libc.so.1
libz.so => /lib/64/libz.so
libnsl.so.1 => /lib/64/libnsl.so.1
libmp.so.2 => /lib/64/libmp.so.2
libmd.so.1 => /lib/64/libmd.so.1
libm.so.2 => /lib/64/libm.so.2
$ ./do_test_static
PQlibVersion=130000
$
$ make do_test_static_wholearchive
gcc -o do_test_static_wholearchive -Wall -Werror -I"/opt/ooce/pgsql-13/include" do_test.c -L"/opt/ooce/pgsql-13/lib/amd64" -Wl,-Bstatic -Wl,--whole-archive -lpq -lpgcommon -lpgport -Wl,--no-whole-archive -Wl,-Bdynamic -lssl -lcrypto -lsocket
ld: fatal: symbol 'pqsignal' is multiply-defined:
(file /opt/ooce/pgsql-13/lib/amd64/libpq.a(legacy-pqsignal.o) type=FUNC; file /opt/ooce/pgsql-13/lib/amd64/libpgport.a(pqsignal.o) type=FUNC);
ld: fatal: file processing errors. No output written to do_test_static_wholearchive
collect2: error: ld returned 1 exit status
make: *** [GNUmakefile:17: do_test_static_wholearchive] Error 1
Sure enough, those two .a files each have a symbol called "pqsignal", and they are not the same.
$ uname -a
SunOS epsilon3 5.11 helios-1.0.20664 i86pc i386 i86pc illumos
$ make --version
GNU Make 4.3
Built for x86_64-pc-solaris2.11
Copyright (C) 1988-2020 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
$ gcc --version
gcc (Helios 1/10.2.0-il-0) 10.2.0
Copyright (C) 2020 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
$ pg_config
BINDIR = /opt/ooce/pgsql-13/bin
DOCDIR = /opt/ooce/pgsql-13/share/doc
HTMLDIR = /opt/ooce/pgsql-13/share/doc
INCLUDEDIR = /opt/ooce/pgsql-13/include
PKGINCLUDEDIR = /opt/ooce/pgsql-13/include
INCLUDEDIR-SERVER = /opt/ooce/pgsql-13/include/server
LIBDIR = /opt/ooce/pgsql-13/lib/amd64
PKGLIBDIR = /opt/ooce/pgsql-13/lib/amd64
LOCALEDIR = /opt/ooce/pgsql-13/share/locale
MANDIR = /opt/ooce/pgsql-13/share/man
SHAREDIR = /opt/ooce/pgsql-13/share
SYSCONFDIR = /etc/opt/ooce/pgsql-13
PGXS = /opt/ooce/pgsql-13/lib/amd64/pgxs/src/makefiles/pgxs.mk
CONFIGURE = '--includedir=/opt/ooce/pgsql-13/include' '--bindir=/opt/ooce/pgsql-13/bin/amd64' '--sbindir=/opt/ooce/pgsql-13/sbin/amd64' '--libdir=/opt/ooce/pgsql-13/lib/amd64' '--libexecdir=/opt/ooce/pgsql-13/libexec/amd64' '--bindir=/opt/ooce/pgsql-13/bin' '--enable-dtrace' 'DTRACEFLAGS=-64' '--prefix=/opt/ooce/pgsql-13' '--sysconfdir=/etc/opt/ooce/pgsql-13' '--localstatedir=/var/opt/ooce/pgsql-13' '--enable-thread-safety' '--with-openssl' '--with-libxml' '--with-xslt' '--with-readline' '--without-systemd' '--with-system-tzdata=/usr/share/lib/zoneinfo' 'CC=gcc' 'CFLAGS= -O2 -fno-aggressive-loop-optimizations -O3 -m64' 'LDFLAGS= -m64' 'CPPFLAGS= ' 'CXX=g++' 'CXXFLAGS= -O2 -fno-aggressive-loop-optimizations -m64' 'PKG_CONFIG_PATH=/opt/ooce/lib/amd64/pkgconfig'
CC = gcc
CPPFLAGS = -I/usr/include/libxml2
CFLAGS = -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wimplicit-fallthrough=3 -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -Wno-format-truncation -Wno-stringop-truncation -O2 -fno-aggressive-loop-optimizations -O3 -m64
CFLAGS_SL = -fPIC
LDFLAGS = -m64 -L/usr/lib/amd64 -Wl,-R'/opt/ooce/pgsql-13/lib/amd64'
LDFLAGS_EX =
LDFLAGS_SL =
LIBS = -lpgcommon -lpgport -lxml2 -lssl -lcrypto -lz -lreadline -ltermcap -lnsl -lsocket -lm
VERSION = PostgreSQL 13.0
The output above is from Helios, but the same behavior is reproducible with Linux as well.
[ec2-user@ip-172-31-40-169 libpq_test]$ uname -a
Linux ip-172-31-40-169.us-west-2.compute.internal 4.14.243-185.433.amzn2.x86_64 #1 SMP Mon Aug 9 05:55:52 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
[ec2-user@ip-172-31-40-169 libpq_test]$ make --version
GNU Make 3.82
Built for x86_64-koji-linux-gnu
Copyright (C) 2010 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
[ec2-user@ip-172-31-40-169 libpq_test]$ gcc --version
gcc (GCC) 7.3.1 20180712 (Red Hat 7.3.1-13)
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
[ec2-user@ip-172-31-40-169 libpq_test]$ pg_config
BINDIR = /home/ec2-user/postgres-install/bin
DOCDIR = /home/ec2-user/postgres-install/share/doc
HTMLDIR = /home/ec2-user/postgres-install/share/doc
INCLUDEDIR = /home/ec2-user/postgres-install/include
PKGINCLUDEDIR = /home/ec2-user/postgres-install/include
INCLUDEDIR-SERVER = /home/ec2-user/postgres-install/include/server
LIBDIR = /home/ec2-user/postgres-install/lib
PKGLIBDIR = /home/ec2-user/postgres-install/lib
LOCALEDIR = /home/ec2-user/postgres-install/share/locale
MANDIR = /home/ec2-user/postgres-install/share/man
SHAREDIR = /home/ec2-user/postgres-install/share
SYSCONFDIR = /home/ec2-user/postgres-install/etc
PGXS = /home/ec2-user/postgres-install/lib/pgxs/src/makefiles/pgxs.mk
CONFIGURE = '--without-readline' '--prefix=/home/ec2-user/postgres-install'
CC = gcc
CPPFLAGS = -D_GNU_SOURCE
CFLAGS = -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wimplicit-fallthrough=3 -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -Wno-format-truncation -O2
CFLAGS_SL = -fPIC
LDFLAGS = -Wl,--as-needed -Wl,-rpath,'/home/ec2-user/postgres-install/lib',--enable-new-dtags
LDFLAGS_EX =
LDFLAGS_SL =
LIBS = -lpgcommon -lpgport -lpthread -lz -lrt -ldl -lm
VERSION = PostgreSQL 13.4