[Buildroot] [PATCH 3 of 5 RFC] dependencies: build a host-tar if no suitable tar can be found

[Thomas De Schampheleire <patrickdepinguin+buildroot@gmail.com>]

Some toolchains, like the one built with buildroot itself, use hardlinks (for
example to link between the c++ and g++ binary). Unpacking such a toolchain
with the --strip-components options does not work correctly if the system tar
is too old (<1.17). Even recent releases of RedHat/CentOS still ship with
tar 1.15.

This patch checks for a suitable tar version (tar 1.17+) on the host system,
and adds host-tar to the host dependencies if none can be found.

TAR is redefined to HOST_TAR, except when extracting host-tar (this is a
chicken-and-egg problem), so that all packages use the host-tar if no suitable
tar was found.

Along with this patch, the definition of TAR_STRIP_COMPONENTS was moved to
check-host-tar.mk.

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>

---
 package/Makefile.package.in              |  12 ------------
 package/tar/tar.mk                       |   4 ++++
 toolchain/dependencies/check-host-tar.mk |  24 ++++++++++++++++++++++++
 toolchain/dependencies/check-host-tar.sh |  29 +++++++++++++++++++++++++++++
 4 files changed, 57 insertions(+), 12 deletions(-)

diff --git a/package/Makefile.package.in b/package/Makefile.package.in
--- a/package/Makefile.package.in
+++ b/package/Makefile.package.in
@@ -235,18 +235,6 @@ define DOWNLOAD
 	exit 1
 endef
 
-# Utility programs used to build packages
-TAR ?= tar
-
-# Automatically detect tar --strip-path/components option
-TAR_STRIP_COMPONENTS := \
-  $(shell $(TAR) --help | grep strip-path > /dev/null ; \
-  if test $$? = 0 ; then \
-   echo '--strip-path' ; \
-  else \
-   echo '--strip-components' ; \
-  fi)
-
 # Needed for the foreach loops to loop over the list of hooks, so that
 # each hook call is properly separated by a newline.
 define sep
diff --git a/package/tar/tar.mk b/package/tar/tar.mk
--- a/package/tar/tar.mk
+++ b/package/tar/tar.mk
@@ -8,3 +8,7 @@ TAR_VERSION = 1.26
 TAR_SITE = $(BR2_GNU_MIRROR)/tar
 
 $(eval $(call AUTOTARGETS))
+
+TAR := $(SYSTEM_TAR) # We need a real tar to extract tar
+$(eval $(call AUTOTARGETS,host))
+TAR := $(HOST_TAR)
diff --git a/toolchain/dependencies/check-host-tar.mk b/toolchain/dependencies/check-host-tar.mk
new file mode 100644
--- /dev/null
+++ b/toolchain/dependencies/check-host-tar.mk
@@ -0,0 +1,24 @@
+TAR ?= tar
+SYSTEM_TAR := $(TAR)
+
+ifneq (,$(call suitable-host-package,tar))
+  HOST_TAR := $(TAR)
+
+  # Automatically detect tar --strip-path/components option
+  # --strip-path was renamed to --strip-components in tar 1.15
+  TAR_STRIP_COMPONENTS := \
+    $(shell $(TAR) --help | grep strip-path > /dev/null ; \
+    if test $$? = 0 ; then \
+     echo '--strip-path' ; \
+    else \
+     echo '--strip-components' ; \
+    fi)
+
+else
+  DEPENDENCIES_HOST_PREREQ += host-tar
+  HOST_TAR := $(HOST_DIR)/usr/bin/tar
+  TAR_STRIP_COMPONENTS := --strip-components
+
+endif
+
+TAR := $(HOST_TAR)
diff --git a/toolchain/dependencies/check-host-tar.sh b/toolchain/dependencies/check-host-tar.sh
new file mode 100755
--- /dev/null
+++ b/toolchain/dependencies/check-host-tar.sh
@@ -0,0 +1,29 @@
+#!/bin/sh
+
+tar=`which tar`
+if [ -z "$tar" ]; then
+	return
+fi
+
+# Output of 'tar --version' examples:
+# tar (GNU tar) 1.15.1 
+# tar (GNU tar) 1.25
+version=`$tar --version | head -n 1 | sed 's/^.*\s\([0-9]\+\.\S\+\).*$/\1/'`
+major=`echo "$version" | cut -d. -f1`
+minor=`echo "$version" | cut -d. -f2`
+bugfix=`echo "$version" | cut -d. -f3`
+
+# Minimal version = 1.17 (previous versions do not correctly unpack archives
+# containing hard-links if the --strip-components option is used).
+major_min=1
+minor_min=17
+if [ $major -gt $major_min ]; then
+	echo $tar
+else
+	if [ $major -eq $major_min -a $minor -ge $minor_min ]; then
+		echo $tar
+	else
+		false
+		# echo nothing: no suitable tar found
+	fi
+fi