Upstream-status: https://github.com/LIJI32/SameBoy/pull/662

diff --git a/Makefile b/Makefile
index a1bce3e..cea556e 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,14 @@
 # Make hacks
 .INTERMEDIATE:
 
+# Library versioning, following libtool's 'version-info' scheme (see:
+# info '(libtool) Libtool versioning' or
+# https://www.gnu.org/software/libtool/manual/html_node/Libtool-versioning.html).
+LT_CURRENT := 0
+LT_REVISION := 0
+LT_AGE := 0
+LT_VERSION_INFO := $(LT_CURRENT):$(LT_REVISION):$(LT_AGE)
+
 # Set target, configuration, version and destination folders
 
 PLATFORM := $(shell uname -s)
@@ -33,11 +41,47 @@ else
 DEFAULT := sdl
 endif
 
+ifneq ($(LIBRARY),)
+DEFAULT += lib
+endif
+
+# Select whether libtool should build/link for static vs shared
+# libraries, or both.
+ifneq ($(LIBRARY),)
+ifeq ($(LIBRARY), shared)
+LT_MODE_ARG := -shared
+else ifeq ($(LIBRARY), static)
+LT_MODE_ARG := -static
+else
+# Build both static and shared libraries.
+LT_MODE_ARG :=
+endif
+endif
+
 NULL := /dev/null
 ifeq ($(PLATFORM),windows32)
 NULL := NUL
 endif
 
+# Strip a given prefix from a string.
+# arg1: The prefix to strip.
+# arg2: The text containing the prefix.
+# Return $text with $prefix stripped, else nothing.
+define strip_prefix =
+$(let stripped,$(subst $(1),,$(2)),$\
+  $(shell test "$(1)$(stripped)" = "$(2)" && echo $(stripped)))
+endef
+
+# Simplify a path for use with pkg-config, by replacing $prefix with '${prefix}'
+# arg1: prefix, e.g. an installation prefix, such as /usr/local.
+# arg2: pkgdir, e.g. a path such as $datadir, $bindir, etc.
+# arg3: pkg-config variable name, e.g. 'prefix' or 'exec_prefix'.
+#       Defaults to 'prefix'.
+define simplify_pkgconf_dir =
+$(let stripped,$(call strip_prefix,$(1),$(2)),$\
+  $(if stripped,$${$(or $(3),prefix)}$(stripped),$(2)))
+endef
+
 ifneq ($(shell which xdg-open 2> $(NULL))$(FREEDESKTOP),)
 # Running on an FreeDesktop environment, configure for (optional) installation
 DESTDIR ?= 
@@ -46,6 +90,22 @@ DATA_DIR ?= $(PREFIX)/share/sameboy/
 FREEDESKTOP ?= true
 endif
 
+# Autoconf-style conventionally named variables.
+prefix ?= $(PREFIX)
+exec_prefix ?= $(prefix)
+includedir ?= $(prefix)/include
+bindir ?= $(exec_prefix)/bin
+libdir ?= $(exec_prefix)/lib
+datadir ?= $(prefix)/share
+
+# Prettified variants for use in the pkg-config file.
+override PKGCONF_EXEC_PREFIX = \
+	$(call simplify_pkgconf_dir,$(prefix),$(exec_prefix))
+override PKGCONF_INCLUDEDIR = \
+	$(call simplify_pkgconf_dir,$(prefix),$(includedir))
+override PKGCONF_LIBDIR = \
+	$(call simplify_pkgconf_dir,$(exec_prefix),$(libdir),exec_prefix)
+
 default: $(DEFAULT)
 
 ifeq ($(MAKECMDGOALS),)
@@ -101,6 +161,9 @@ BIN := build/bin
 OBJ := build/obj
 INC := build/include/sameboy
 LIBDIR := build/lib
+PKGCONF_DIR := $(LIBDIR)/pkgconfig
+LIBTOOL_LIBRARY := $(LIBDIR)/libsameboy.la
+PKGCONF_FILE := $(PKGCONF_DIR)/sameboy.pc
 
 BOOTROMS_DIR ?= $(BIN)/BootROMs
 
@@ -125,6 +188,26 @@ PKG_CONFIG := pkg-config
 endif
 endif
 
+# Libtool makes it easy to correctly build shared libraries with
+# version info on both MacOS and GNU/Linux; require it if building
+# libraries.
+ifneq ($(LIBRARY),)
+ifneq (, $(shell command -v libtool 2> $(NULL)))
+LIBTOOL := libtool
+LIBTOOL_CC := $(LIBTOOL) --tag=CC --mode=compile $(CC) -c
+LIBTOOL_LD := $(LIBTOOL) --tag=CC --mode=link $(CC) \
+	-version-info $(LT_VERSION_INFO) $(LT_MODE_ARG)
+else
+$(error "please install libtool")
+endif
+else
+# Not building libraries.
+LIBTOOL :=
+LIBTOOL_CC := $(CC)
+LIBTOOL_LD :=
+endif
+
+
 ifeq ($(PLATFORM),windows32)
 # To force use of the Unix version instead of the Windows version
 MKDIR := $(shell which mkdir)
@@ -276,11 +359,6 @@ LDFLAGS += -Wl,/NODEFAULTLIB:libcmt.lib
 endif
 endif
 
-LIBFLAGS := -nostdlib -Wl,-r
-ifneq ($(PLATFORM),Darwin)
-LIBFLAGS += -no-pie
-endif
-
 ifeq ($(CONF),debug)
 CFLAGS += -g
 else ifeq ($(CONF), release)
@@ -336,11 +414,14 @@ tester: $(TESTER_TARGET) $(BIN)/tester/dmg_boot.bin $(BIN)/tester/cgb_boot.bin $
 _ios: $(BIN)/SameBoy-iOS.app $(OBJ)/installer
 ios-ipa: $(BIN)/SameBoy-iOS.ipa
 ios-deb: $(BIN)/SameBoy-iOS.deb
+
+# Libraries.
 ifeq ($(PLATFORM),windows32)
 lib: lib-unsupported
-else
-lib: $(LIBDIR)/libsameboy.o $(LIBDIR)/libsameboy.a
+else ifneq ($(LIBRARY),)
+lib: $(LIBTOOL_LIBRARY) $(PKGCONF_FILE)
 endif
+
 all: sdl tester libretro lib
 ifeq ($(PLATFORM),Darwin)
 all: cocoa ios-ipa ios-deb
@@ -361,6 +442,10 @@ CORE_SOURCES += $(shell ls Windows/*.c)
 endif
 
 CORE_OBJECTS := $(patsubst %,$(OBJ)/%.o,$(CORE_SOURCES))
+# Libtool PIC objects are created along the .o variants, when building
+# a shared library.
+CORE_LOBJECTS := $(patsubst %,$(OBJ)/%.lo,$(CORE_SOURCES))
+$(CORE_LOBJECTS): $(CORE_OBJECTS)
 PUBLIC_HEADERS := $(patsubst Core/%,$(INC)/%,$(CORE_HEADERS))
 COCOA_OBJECTS := $(patsubst %,$(OBJ)/%.o,$(COCOA_SOURCES))
 IOS_OBJECTS := $(patsubst %,$(OBJ)/%.o,$(IOS_SOURCES))
@@ -404,30 +489,30 @@ $(OBJ)/%.dep: %
 
 $(OBJ)/Core/%.c.o: Core/%.c
 	-@$(MKDIR) -p $(dir $@)
-	$(CC) $(CFLAGS) $(FAT_FLAGS) -DGB_INTERNAL -c $< -o $@
+	$(LIBTOOL_CC) $(CFLAGS) $(FAT_FLAGS) -DGB_INTERNAL -c $< -o $@
 
 $(OBJ)/SDL/%.c.o: SDL/%.c
 	-@$(MKDIR) -p $(dir $@)
-	$(CC) $(CFLAGS) $(FRONTEND_CFLAGS) $(FAT_FLAGS) $(SDL_CFLAGS) $(GL_CFLAGS) -c $< -o $@
+	$(LIBTOOL_CC) $(CFLAGS) $(FRONTEND_CFLAGS) $(FAT_FLAGS) $(SDL_CFLAGS) $(GL_CFLAGS) -c $< -o $@
 
 $(OBJ)/OpenDialog/%.c.o: OpenDialog/%.c
 	-@$(MKDIR) -p $(dir $@)
-	$(CC) $(CFLAGS) $(FRONTEND_CFLAGS) $(FAT_FLAGS) $(SDL_CFLAGS) $(GL_CFLAGS) -c $< -o $@
+	$(LIBTOOL_CC) $(CFLAGS) $(FRONTEND_CFLAGS) $(FAT_FLAGS) $(SDL_CFLAGS) $(GL_CFLAGS) -c $< -o $@
 
 
 $(OBJ)/%.c.o: %.c
 	-@$(MKDIR) -p $(dir $@)
-	$(CC) $(CFLAGS) $(FRONTEND_CFLAGS) $(FAT_FLAGS) -c $< -o $@
+	$(LIBTOOL_CC) $(CFLAGS) $(FRONTEND_CFLAGS) $(FAT_FLAGS) -c $< -o $@
 	
 # HexFiend requires more flags
 $(OBJ)/HexFiend/%.m.o: HexFiend/%.m
 	-@$(MKDIR) -p $(dir $@)
-	$(CC) $(CFLAGS) $(FRONTEND_CFLAGS) $(FAT_FLAGS) $(OCFLAGS) -c $< -o $@ -fno-objc-arc -include HexFiend/HexFiend_2_Framework_Prefix.pch
+	$(LIBTOOL_CC) $(CFLAGS) $(FRONTEND_CFLAGS) $(FAT_FLAGS) $(OCFLAGS) -c $< -o $@ -fno-objc-arc -include HexFiend/HexFiend_2_Framework_Prefix.pch
 	
 $(OBJ)/%.m.o: %.m
 	-@$(MKDIR) -p $(dir $@)
-	$(CC) $(CFLAGS) $(FRONTEND_CFLAGS) $(FAT_FLAGS) $(OCFLAGS) -c $< -o $@
-    
+	$(LIBTOOL_CC) $(CFLAGS) $(FRONTEND_CFLAGS) $(FAT_FLAGS) $(OCFLAGS) -c $< -o $@
+
 # iOS Port
 
 $(BIN)/SameBoy-iOS.app: $(BIN)/SameBoy-iOS.app/SameBoy \
@@ -653,15 +738,28 @@ libretro:
 # Does not install mimetype icons because FreeDesktop is cursed abomination with no right to exist.
 # If you somehow find a reasonable way to make associate an icon with an extension in this dumpster
 # fire of a desktop environment, open an issue or a pull request
+# Install for Linux, and other FreeDesktop platforms.
+install_headers = install -Dm 644 -t $(DESTDIR)$(includedir)/sameboy $(INC)/*
+install_pkgconf_file = install -Dm 644 -t $(DESTDIR)$(libdir)/pkgconfig $(PKGCONF_FILE)
+
 ifneq ($(FREEDESKTOP),)
 ICON_NAMES := apps/sameboy mimetypes/x-gameboy-rom mimetypes/x-gameboy-color-rom
 ICON_SIZES := 16x16 32x32 64x64 128x128 256x256 512x512
 ICONS := $(foreach name,$(ICON_NAMES), $(foreach size,$(ICON_SIZES),$(DESTDIR)$(PREFIX)/share/icons/hicolor/$(size)/$(name).png))
+ifneq ($(LIBRARY),)
+install: lib pkgconf
+endif
+
 install: sdl $(DESTDIR)$(PREFIX)/share/mime/packages/sameboy.xml $(ICONS) FreeDesktop/sameboy.desktop
 	-@$(MKDIR) -p $(dir $(DESTDIR)$(PREFIX))
 	mkdir -p $(DESTDIR)$(DATA_DIR)/ $(DESTDIR)$(PREFIX)/bin/
 	cp -rf $(BIN)/SDL/* $(DESTDIR)$(DATA_DIR)/
 	mv $(DESTDIR)$(DATA_DIR)/sameboy $(DESTDIR)$(PREFIX)/bin/sameboy
+ifneq ($(LIBRARY),)
+	$(install_headers)
+	$(install_pkgconf_file)
+	$(LIBTOOL) --mode=install install -D $(LIBTOOL_LIBRARY) $(libdir)/libsameboy.la
+endif
 ifeq ($(DESTDIR),)
 	-update-mime-database -n $(PREFIX)/share/mime
 	-xdg-desktop-menu install --novendor --mode system FreeDesktop/sameboy.desktop
@@ -727,20 +825,23 @@ $(OBJ)/control.tar.gz: iOS/deb-postinst iOS/deb-prerm iOS/deb-control
 $(OBJ)/debian-binary:
 	-@$(MKDIR) -p $(dir $@)
 	echo 2.0 > $@
-    
-$(LIBDIR)/libsameboy.o: $(CORE_OBJECTS)
+
+# Link library objects with libtool.
+$(LIBTOOL_LIBRARY): $(CORE_LOBJECTS)
 	-@$(MKDIR) -p $(dir $@)
-	@# This is a somewhat simple hack to force Clang and GCC to build a native object file out of one or many LTO objects
-	echo "static const char __attribute__((used)) x=0;"| $(CC) $(filter-out -flto,$(CFLAGS)) -c -x c - -o $(OBJ)/lto_hack.o
-	@# And this is a somewhat complicated hack to invoke the correct LTO-enabled LD command in a mostly cross-platform nature
-	$(CC) $(FAT_FLAGS) $(CFLAGS) $(LIBFLAGS) $^ $(OBJ)/lto_hack.o -o $@
-	-@rm $(OBJ)/lto_hack.o
-    
-$(LIBDIR)/libsameboy.a: $(LIBDIR)/libsameboy.o
+	$(LIBTOOL_LD) -rpath $(libdir) $^ -o $@
+
+$(PKGCONF_FILE): sameboy.pc.in
 	-@$(MKDIR) -p $(dir $@)
 	-@rm -f $@
-	ar -crs $@ $^
-	
+	sed -e 's,@prefix@,$(prefix),' \
+	 -e 's/@version@/$(VERSION)/' \
+	 -e 's,@exec_prefix@,$(PKGCONF_EXEC_PREFIX),' \
+	 -e 's,@includedir@,$(PKGCONF_INCLUDEDIR),' \
+	 -e 's,@libdir@,$(PKGCONF_LIBDIR),' $< > $@
+
+pkgconf: $(PKGCONF_FILE)
+
 $(INC)/%.h: Core/%.h
 	-@$(MKDIR) -p $(dir $@)
 	-@# CPPP doesn't like multibyte characters, so we replace the single quote character before processing so it doesn't complain
@@ -754,4 +855,4 @@ lib-unsupported:
 clean:
 	rm -rf build
 
-.PHONY: libretro tester cocoa ios _ios ios-ipa ios-deb liblib-unsupported bootroms
+.PHONY: libretro tester cocoa ios _ios ios-ipa ios-deb lib lib-unsupported bootroms pkgconf
diff --git a/README.md b/README.md
index 9c5f8da..e23f2ca 100644
--- a/README.md
+++ b/README.md
@@ -53,12 +53,18 @@ On Windows, SameBoy also requires:
 To compile, simply run `make`. The targets are:
  * `cocoa` (Default for macOS)
  * `sdl` (Default for everything else)
- * `lib` (Creates libsameboy.o and libsameboy.a for statically linking SameBoy, as well as a headers directory with corresponding headers; currently not supported on Windows due to linker limitations)
+ * `lib` (Creates libsameboy.o, libsameboy.a and libsameboy.so for linking SameBoy, as well as a headers directory with corresponding headers; currently not supported on Windows due to linker limitations)
  * `ios` (Plain iOS .app bundle), `ios-ipa` (iOS IPA archive for side-loading), `ios-deb` (iOS deb package for jailbroken devices)
  * `libretro`
  * `bootroms`
  * `tester` 
 
+For convenience, when installing the static and shared libraries is
+desired, you can specify the LIBRARY=1 make variable to have the
+libraries built as part of the default target, as well as installed,
+along the headers. Alternatively, `LIBRARY=shared` will install just
+the shared library, while `LIBRARY=static` only the static one.
+
 You may also specify `CONF=debug` (default), `CONF=release`, `CONF=native_release` or `CONF=fat_release`  to control optimization, symbols and multi-architectures. `native_release` is faster than `release`, but is optimized to the host's CPU and therefore is not portable. `fat_release` is exclusive to macOS and builds x86-64 and ARM64 fat binaries; this requires using a recent enough `clang` and macOS SDK using `xcode-select`, or setting them explicitly with `CC=` and `SYSROOT=`, respectively. All other configurations will build to your host architecture, except for the iOS targets. You may set `BOOTROMS_DIR=...` to a directory containing precompiled boot ROM files, otherwise the build system will compile and use SameBoy's own boot ROMs.
 
 The SDL port will look for resource files with a path relative to executable and inside the directory specified by the `DATA_DIR` variable. If you are packaging SameBoy, you may wish to override this by setting the `DATA_DIR` variable during compilation to the target path of the directory containing all files (apart from the executable, that's not necessary) from the `build/bin/SDL` directory in the source tree. Make sure the variable ends with a `/` character. On FreeDesktop environments, `DATA_DIR` will default to `/usr/local/share/sameboy/`. `PREFIX` and `DESTDIR` follow their standard usage and default to an empty string an `/usr/local`, respectively
diff --git a/sameboy.pc.in b/sameboy.pc.in
new file mode 100644
index 0000000..dc0ca0b
--- /dev/null
+++ b/sameboy.pc.in
@@ -0,0 +1,10 @@
+prefix=@prefix@
+exec_prefix=@exec_prefix@
+includedir=@includedir@
+libdir=@libdir@
+
+Name: sameboy
+Description: The SameBoy library
+Version: @version@
+Cflags: -I${includedir}/sameboy
+Libs: -L${libdir} -lsameboy