[Buildroot] [PATCH v2] Don't build host-cmake if it is available on the build host

Fri Feb 5 11:07:56 UTC 2016

Currently all cmake packages depend on host-cmake. Unfortunately
host-cmake takes a long time to configure and build: almost 7 minutes
on a dual-core i5 with SSD. The time does not change even with ccache
enabled.

Indeed, building host-cmake is avoidable if it is already installed on
the build host: CMake is supposed to be quite portable, and the only
patch in Buildroot for the CMake package seems to only affect
target-cmake.

We avoid building host-cmake if cmake is already available on the host
using a technique similar to the one used for host-tar and host-xzcat.

First, we leverage the existing infrastructure in
support/dependencies/dependencies.mk to set CMAKE to either "cmake" or
"$(HOST_DIR)/usr/bin/cmake". In the latter case we also set
BUILD_HOST_CMAKE = YES meaning we need to build and use host-cmake.

Then in pkg-cmake.mk we launch $(CMAKE) instead of
$(HOST_DIR)/usr/bin/cmake.

Finally, we do skip adding the dependency on host-cmake for all cmake
packages when $(BUILD_HOST_CMAKE) != YES.

Unlike what we do for host-tar and host-xzcat, for host-cmake we do
not add host-cmake to DEPENDENCIES_HOST_PREREQ. If we did, host-cmake
would be a dependency for _any_ package when it's not installed on the
host, even when no cmake package is selected.

check-host-cmake.sh requires CMake to be at least 3.0 to consider it
suitable. This is because older versions are affected by the bug
described and fixed in Buildroot in ef2c1970e4bf ("cmake: add patch to
fix Qt mkspecs detection"). The bug was fixed in upstream CMake in
version 3.0 [0].

Besides, among all the cmake packages currently in Buildroot, the
highest version mentioned in cmake_minimum_required() is 3.0 (the
grantlee package). Thus 3.0 should be enough to build all current
packages. Of course, with the addition or bump of packages, the
minimum required version will raise.

Tested on:
 - Ubuntu 14.04 without CMake, with official CMake (2.8), PPA CMake
   (3.2)
 - Ubuntu 15.10 without CMake, with official CMake (3.2)

[0] https://cmake.org/gitweb?p=cmake.git;h=e8b8b37ef6fef094940d3384df5a1d421b9fa568

Signed-off-by: Luca Ceresoli <luca at lucaceresoli.net>
Cc: Samuel Martin <s.martin49 at gmail.com>
Cc: Davide Viti <zinosat at tiscali.it>
Cc: Arnout Vandecappelle <arnout at mind.be>

---

Note: there is still a pending clarification with Arnout about this
patch. I'm sending it anyway since v1 is broken, and this one has
improvements in addition to the bugfix.

On my build server, this patch reduced the build time for a batch of
16 Buildroot configurations (all building cmake-based packages) from
2h44m to 1h54m. Woah, it's a 30% saving!

Changes v1 -> v2:
 - Require cmake >= 3.0. Fixes qjson failure (Luca, Samuel, Thomas)
 - In check-host-cmake.sh only search $1, not "cmake" (Arnout)
 - typo: host-ccache -> host-cmake (Arnout)
---
 package/pkg-cmake.mk                     |  6 ++++--
 support/dependencies/check-host-cmake.mk |  6 ++++++
 support/dependencies/check-host-cmake.sh | 30 ++++++++++++++++++++++++++++++
 3 files changed, 40 insertions(+), 2 deletions(-)
 create mode 100644 support/dependencies/check-host-cmake.mk
 create mode 100755 support/dependencies/check-host-cmake.sh

diff --git a/package/pkg-cmake.mk b/package/pkg-cmake.mk
index 81dcfcc..e3bd603 100644
--- a/package/pkg-cmake.mk
+++ b/package/pkg-cmake.mk
@@ -85,7 +85,7 @@ define $(2)_CONFIGURE_CMDS
 	cd $$($$(PKG)_BUILDDIR) && \
 	rm -f CMakeCache.txt && \
 	PATH=$$(BR_PATH) \
-	$$($$(PKG)_CONF_ENV) $$(HOST_DIR)/usr/bin/cmake $$($$(PKG)_SRCDIR) \
+	$$($$(PKG)_CONF_ENV) $$(CMAKE) $$($$(PKG)_SRCDIR) \
 		-DCMAKE_TOOLCHAIN_FILE="$$(HOST_DIR)/usr/share/buildroot/toolchainfile.cmake" \
 		-DCMAKE_BUILD_TYPE=$$(if $$(BR2_ENABLE_DEBUG),Debug,Release) \
 		-DCMAKE_INSTALL_PREFIX="/usr" \
@@ -110,7 +110,7 @@ define $(2)_CONFIGURE_CMDS
 	cd $$($$(PKG)_BUILDDIR) && \
 	rm -f CMakeCache.txt && \
 	PATH=$$(BR_PATH) \
-	$$(HOST_DIR)/usr/bin/cmake $$($$(PKG)_SRCDIR) \
+	$$(CMAKE) $$($$(PKG)_SRCDIR) \
 		-DCMAKE_INSTALL_SO_NO_EXE=0 \
 		-DCMAKE_FIND_ROOT_PATH="$$(HOST_DIR)" \
 		-DCMAKE_FIND_ROOT_PATH_MODE_PROGRAM="BOTH" \
@@ -149,7 +149,9 @@ $(2)_DEPENDENCIES ?= $$(filter-out host-skeleton host-toolchain $(1),\
 	$$(patsubst host-host-%,host-%,$$(addprefix host-,$$($(3)_DEPENDENCIES))))
 endif
 
+ifeq ($$(BUILD_HOST_CMAKE),YES)
 $(2)_DEPENDENCIES += host-cmake
+endif
 
 #
 # Build step. Only define it if not already defined by the package .mk
diff --git a/support/dependencies/check-host-cmake.mk b/support/dependencies/check-host-cmake.mk
new file mode 100644
index 0000000..fe16322
--- /dev/null
+++ b/support/dependencies/check-host-cmake.mk
@@ -0,0 +1,6 @@
+CMAKE ?= cmake
+
+ifeq (,$(call suitable-host-package,cmake,$(CMAKE)))
+BUILD_HOST_CMAKE = YES
+CMAKE = $(HOST_DIR)/usr/bin/cmake
+endif
diff --git a/support/dependencies/check-host-cmake.sh b/support/dependencies/check-host-cmake.sh
new file mode 100755
index 0000000..08de60c
--- /dev/null
+++ b/support/dependencies/check-host-cmake.sh
@@ -0,0 +1,30 @@
+#!/bin/sh
+
+candidate="$1"
+
+cmake=`which $candidate`
+if [ ! -x "$cmake" ]; then
+	# echo nothing: no suitable cmake found
+	exit 1
+fi
+
+version=`$cmake --version | head -n1 | cut -d\  -f3`
+major=`echo "$version" | cut -d. -f1`
+minor=`echo "$version" | cut -d. -f2`
+
+# Versions before 3.0 are affected by the bug described in
+# https://git.busybox.net/buildroot/commit/?id=ef2c1970e4bff3be3992014070392b0e6bc28bd2
+# and fixed in upstream CMake in version 3.0:
+# https://cmake.org/gitweb?p=cmake.git;h=e8b8b37ef6fef094940d3384df5a1d421b9fa568
+major_min=3
+minor_min=0
+if [ $major -gt $major_min ]; then
+	echo $cmake
+else
+	if [ $major -eq $major_min -a $minor -ge $minor_min ]; then
+		echo $cmake
+	else
+		# echo nothing: no suitable cmake found
+		exit 1
+	fi
+fi
-- 
1.9.1

