Apply OS checks to host platform, not build

Previously, the build system used uname(1) output when it wanted to
check the operating system it was being built for, which meant that it
didn't take into-account cross-compilation when the build and host
operating systems were different.

To fix this, instead of consulting uname output, we consult the host
triple, specifically the third "kernel" part.

For "kernel"s with stable ABIs, like Linux or Cygwin, we can use a
simple ifeq to test whether we're compiling for that system, but for
other platforms, like Darwin, FreeBSD, or Solaris, we have to use a
more complicated check to take into account the version numbers at the
end of the "kernel"s.  I couldn't find a way to just strip these
version numbers in GNU Make without shelling out, which would be even
more ugly IMO.  Because these checks differ between kernels, and the
patsubst ones are quite fiddly, I've added variables for each host OS
we might want to check to make them easier to reuse.

13 files changed, 48 insertions, 27 deletions

diff --git a/Makefile.config.in b/Makefile.config.in
index fd92365eb..c8c4446b4 100644
--- a/Makefile.config.in
+++ b/Makefile.config.in
@@ -1,3 +1,4 @@
+HOST_OS = @host_os@
 AR = @AR@
 BDW_GC_LIBS = @BDW_GC_LIBS@
 BOOST_LDFLAGS = @BOOST_LDFLAGS@
diff --git a/misc/launchd/local.mk b/misc/launchd/local.mk
index 0ba722efb..a39188fe6 100644
--- a/misc/launchd/local.mk
+++ b/misc/launchd/local.mk
@@ -1,4 +1,4 @@
-ifeq ($(OS), Darwin)
+ifdef HOST_DARWIN
 
   $(eval $(call install-data-in, $(d)/org.nixos.nix-daemon.plist, $(prefix)/Library/LaunchDaemons))
 
diff --git a/misc/systemd/local.mk b/misc/systemd/local.mk
index 785db52a4..1fa037485 100644
--- a/misc/systemd/local.mk
+++ b/misc/systemd/local.mk
@@ -1,4 +1,4 @@
-ifeq ($(OS), Linux)
+ifdef HOST_LINUX
 
   $(foreach n, nix-daemon.socket nix-daemon.service, $(eval $(call install-file-in, $(d)/$(n), $(prefix)/lib/systemd/system, 0644)))
 
diff --git a/misc/upstart/local.mk b/misc/upstart/local.mk
index 5071676dc..2fbfb29b9 100644
--- a/misc/upstart/local.mk
+++ b/misc/upstart/local.mk
@@ -1,4 +1,4 @@
-ifeq ($(OS), Linux)
+ifdef HOST_LINUX
 
   $(foreach n, nix-daemon.conf, $(eval $(call install-file-in, $(d)/$(n), $(sysconfdir)/init, 0644)))
 
diff --git a/mk/lib.mk b/mk/lib.mk
index 975102531..92f0983d5 100644
--- a/mk/lib.mk
+++ b/mk/lib.mk
@@ -10,8 +10,25 @@ bin-scripts :=
 noinst-scripts :=
 man-pages :=
 install-tests :=
-OS = $(shell uname -s)
 
+ifdef HOST_OS
+  HOST_KERNEL = $(firstword $(subst -, ,$(HOST_OS)))
+  ifeq ($(HOST_KERNEL), cygwin)
+    HOST_CYGWIN = 1
+  endif
+  ifeq ($(patsubst darwin%,,$(HOST_KERNEL)),)
+    HOST_DARWIN = 1
+  endif
+  ifeq ($(patsubst freebsd%,,$(HOST_KERNEL)),)
+    HOST_FREEBSD = 1
+  endif
+  ifeq ($(HOST_KERNEL), linux)
+    HOST_LINUX = 1
+  endif
+  ifeq ($(patsubst solaris%,,$(HOST_KERNEL)),)
+    HOST_SOLARIS = 1
+  endif
+endif
 
 # Hack to define a literal space.
 space :=
@@ -50,16 +67,16 @@ endif
 BUILD_SHARED_LIBS ?= 1
 
 ifeq ($(BUILD_SHARED_LIBS), 1)
-  ifeq (CYGWIN,$(findstring CYGWIN,$(OS)))
+  ifdef HOST_CYGWIN
     GLOBAL_CFLAGS += -U__STRICT_ANSI__ -D_GNU_SOURCE
     GLOBAL_CXXFLAGS += -U__STRICT_ANSI__ -D_GNU_SOURCE
   else
     GLOBAL_CFLAGS += -fPIC
     GLOBAL_CXXFLAGS += -fPIC
   endif
-  ifneq ($(OS), Darwin)
-   ifneq ($(OS), SunOS)
-    ifneq ($(OS), FreeBSD)
+  ifndef HOST_DARWIN
+   ifndef HOST_SOLARIS
+    ifndef HOST_FREEBSD
      GLOBAL_LDFLAGS += -Wl,--no-copy-dt-needed-entries
     endif
    endif
diff --git a/mk/libraries.mk b/mk/libraries.mk
index 7c0e4f100..07bd54dab 100644
--- a/mk/libraries.mk
+++ b/mk/libraries.mk
@@ -1,9 +1,9 @@
 libs-list :=
 
-ifeq ($(OS), Darwin)
+ifdef HOST_DARWIN
   SO_EXT = dylib
 else
-  ifeq (CYGWIN,$(findstring CYGWIN,$(OS)))
+  ifdef HOST_CYGWIN
     SO_EXT = dll
   else
     SO_EXT = so
@@ -59,7 +59,7 @@ define build-library
   $(1)_OBJS := $$(addprefix $(buildprefix), $$(addsuffix .o, $$(basename $$(_srcs))))
   _libs := $$(foreach lib, $$($(1)_LIBS), $$($$(lib)_PATH))
 
-  ifeq (CYGWIN,$(findstring CYGWIN,$(OS)))
+  ifdef HOST_CYGWIN
     $(1)_INSTALL_DIR ?= $$(bindir)
   else
     $(1)_INSTALL_DIR ?= $$(libdir)
@@ -73,18 +73,18 @@ define build-library
   ifeq ($(BUILD_SHARED_LIBS), 1)
 
     ifdef $(1)_ALLOW_UNDEFINED
-      ifeq ($(OS), Darwin)
+      ifdef HOST_DARWIN
         $(1)_LDFLAGS += -undefined suppress -flat_namespace
       endif
     else
-      ifneq ($(OS), Darwin)
-        ifneq (CYGWIN,$(findstring CYGWIN,$(OS)))
+      ifndef HOST_DARWIN
+        ifndef HOST_CYGWIN
           $(1)_LDFLAGS += -Wl,-z,defs
         endif
       endif
     endif
 
-    ifneq ($(OS), Darwin)
+    ifndef HOST_DARWIN
       $(1)_LDFLAGS += -Wl,-soname=$$($(1)_NAME).$(SO_EXT)
     endif
 
@@ -93,7 +93,7 @@ define build-library
     $$($(1)_PATH): $$($(1)_OBJS) $$(_libs) | $$(_d)/
 	$$(trace-ld) $(CXX) -o $$(abspath $$@) -shared $$(LDFLAGS) $$(GLOBAL_LDFLAGS) $$($(1)_OBJS) $$($(1)_LDFLAGS) $$($(1)_LDFLAGS_PROPAGATED) $$(foreach lib, $$($(1)_LIBS), $$($$(lib)_LDFLAGS_USE)) $$($(1)_LDFLAGS_UNINSTALLED)
 
-    ifneq ($(OS), Darwin)
+    ifndef HOST_DARWIN
       $(1)_LDFLAGS_USE += -Wl,-rpath,$$(abspath $$(_d))
     endif
     $(1)_LDFLAGS_USE += -L$$(_d) -l$$(patsubst lib%,%,$$(strip $$($(1)_NAME)))
@@ -108,7 +108,7 @@ define build-library
 	$$(trace-ld) $(CXX) -o $$@ -shared $$(LDFLAGS) $$(GLOBAL_LDFLAGS) $$($(1)_OBJS) $$($(1)_LDFLAGS) $$($(1)_LDFLAGS_PROPAGATED) $$(foreach lib, $$($(1)_LIBS), $$($$(lib)_LDFLAGS_USE_INSTALLED))
 
     $(1)_LDFLAGS_USE_INSTALLED += -L$$(DESTDIR)$$($(1)_INSTALL_DIR) -l$$(patsubst lib%,%,$$(strip $$($(1)_NAME)))
-    ifneq ($(OS), Darwin)
+    ifndef HOST_DARWIN
       ifeq ($(SET_RPATH_TO_LIBS), 1)
         $(1)_LDFLAGS_USE_INSTALLED += -Wl,-rpath,$$($(1)_INSTALL_DIR)
       else
diff --git a/nix-rust/local.mk b/nix-rust/local.mk
index 9650cdf93..538244594 100644
--- a/nix-rust/local.mk
+++ b/nix-rust/local.mk
@@ -11,12 +11,12 @@ libnixrust_INSTALL_PATH := $(libdir)/libnixrust.$(SO_EXT)
 libnixrust_LDFLAGS_USE := -L$(d)/target/$(RUST_DIR) -lnixrust
 libnixrust_LDFLAGS_USE_INSTALLED := -L$(libdir) -lnixrust
 
-ifeq ($(OS), Linux)
+ifdef HOST_LINUX
 libnixrust_LDFLAGS_USE += -ldl
 libnixrust_LDFLAGS_USE_INSTALLED += -ldl
 endif
 
-ifeq ($(OS), Darwin)
+ifdef HOST_DARWIN
 libnixrust_BUILD_FLAGS = NIX_LDFLAGS="-undefined dynamic_lookup"
 else
 libnixrust_LDFLAGS_USE += -Wl,-rpath,$(abspath $(d)/target/$(RUST_DIR))
@@ -31,7 +31,7 @@ $(libnixrust_PATH): $(call rwildcard, $(d)/src, *.rs) $(d)/Cargo.toml
 
 $(libnixrust_INSTALL_PATH): $(libnixrust_PATH)
 	$(target-gen) cp $^ $@
-ifeq ($(OS), Darwin)
+ifdef HOST_DARWIN
 	install_name_tool -id $@ $@
 endif
 
@@ -40,7 +40,7 @@ clean: clean-rust
 clean-rust:
 	$(suppress) rm -rfv nix-rust/target
 
-ifneq ($(OS), Darwin)
+ifndef HOST_DARWIN
 check: rust-tests
 
 rust-tests:
diff --git a/perl/Makefile.config.in b/perl/Makefile.config.in
index eccfbd9f6..d856de3ad 100644
--- a/perl/Makefile.config.in
+++ b/perl/Makefile.config.in
@@ -1,3 +1,4 @@
+HOST_OS = @host_os@
 CC = @CC@
 CFLAGS = @CFLAGS@
 CXX = @CXX@
diff --git a/perl/configure.ac b/perl/configure.ac
index 85183c005..eb65ac17b 100644
--- a/perl/configure.ac
+++ b/perl/configure.ac
@@ -7,6 +7,8 @@ CXXFLAGS=
 AC_PROG_CC
 AC_PROG_CXX
 
+AC_CANONICAL_HOST
+
 # Use 64-bit file system calls so that we can support files > 2 GiB.
 AC_SYS_LARGEFILE
 
diff --git a/perl/local.mk b/perl/local.mk
index b13d4c0d6..0eae651d8 100644
--- a/perl/local.mk
+++ b/perl/local.mk
@@ -28,7 +28,7 @@ Store_CXXFLAGS = \
 
 Store_LDFLAGS := $(SODIUM_LIBS) $(NIX_LIBS)
 
-ifeq (CYGWIN,$(findstring CYGWIN,$(OS)))
+ifdef HOST_CYGWIN
   archlib = $(shell perl -E 'use Config; print $$Config{archlib};')
   libperl = $(shell perl -E 'use Config; print $$Config{libperl};')
   Store_LDFLAGS += $(shell find ${archlib} -name ${libperl})
diff --git a/src/libexpr/local.mk b/src/libexpr/local.mk
index c40abfb78..1aed8e152 100644
--- a/src/libexpr/local.mk
+++ b/src/libexpr/local.mk
@@ -16,7 +16,7 @@ libexpr_CXXFLAGS += -I src/libutil -I src/libstore -I src/libfetchers -I src/lib
 libexpr_LIBS = libutil libstore libfetchers
 
 libexpr_LDFLAGS = -lboost_context
-ifeq ($(OS), Linux)
+ifdef HOST_LINUX
  libexpr_LDFLAGS += -ldl
 endif
 
diff --git a/src/libstore/local.mk b/src/libstore/local.mk
index b6652984c..2fc334a82 100644
--- a/src/libstore/local.mk
+++ b/src/libstore/local.mk
@@ -9,11 +9,11 @@ libstore_SOURCES := $(wildcard $(d)/*.cc $(d)/builtins/*.cc $(d)/build/*.cc)
 libstore_LIBS = libutil
 
 libstore_LDFLAGS = $(SQLITE3_LIBS) -lbz2 $(LIBCURL_LIBS) $(SODIUM_LIBS) -pthread
-ifeq ($(OS), Linux)
+ifdef HOST_LINUX
  libstore_LDFLAGS += -ldl
 endif
 
-ifeq ($(OS), Darwin)
+ifdef HOST_DARWIN
 libstore_FILES = sandbox-defaults.sb sandbox-minimal.sb sandbox-network.sb
 endif
 
@@ -23,7 +23,7 @@ ifeq ($(ENABLE_S3), 1)
 	libstore_LDFLAGS += -laws-cpp-sdk-transfer -laws-cpp-sdk-s3 -laws-cpp-sdk-core
 endif
 
-ifeq ($(OS), SunOS)
+ifdef HOST_SOLARIS
 	libstore_LDFLAGS += -lsocket
 endif
 
diff --git a/src/resolve-system-dependencies/local.mk b/src/resolve-system-dependencies/local.mk
index 054ae01cb..fc48a8417 100644
--- a/src/resolve-system-dependencies/local.mk
+++ b/src/resolve-system-dependencies/local.mk
@@ -1,4 +1,4 @@
-ifeq ($(OS), Darwin)
+ifdef HOST_DARWIN
   programs += resolve-system-dependencies
 endif