sdk: emit proper tag references for base URLs

Properly resolve symbolic tag names when constructing the base feed Git url
and avoid emitting "HEAD" references when building from detached commits.

Fixes #495, #501.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

target/sdk/Makefile

@@ -38,12 +38,14 @@ SDK_DIRS = \
 		$(STAGING_SUBDIR_TOOLCHAIN)
 
 GIT_URL:=$(filter git://% http://% https://%,$(shell git config --get remote.origin.url 2>/dev/null))
-GIT_BRANCH:=$(filter-out master,$(shell git rev-parse --abbrev-ref HEAD 2>/dev/null))
+GIT_COMMIT:=$(shell git rev-parse HEAD 2>/dev/null)
+GIT_BRANCH:=$(filter-out master HEAD,$(shell git rev-parse --abbrev-ref HEAD 2>/dev/null))
+GIT_TAGNAME:=$(shell git show-ref --tags --dereference 2>/dev/null | sed -ne '/^$(GIT_COMMIT) / { s|^.*/||; s|\^.*||; p }')
 
-BASE_FEED:=$(if $(GIT_URL),src-git base $(GIT_URL)$(if $(GIT_BRANCH),;$(GIT_BRANCH)))
+BASE_FEED:=$(if $(GIT_URL),src-git base $(GIT_URL)$(if $(GIT_BRANCH),;$(GIT_BRANCH),$(if $(GIT_TAGNAME),;$(GIT_TAGNAME))))
 BASE_FEED:=$(if $(BASE_FEED),$(BASE_FEED),$(shell cd $(TOPDIR); LC_ALL=C git svn info 2>/dev/null | sed -ne 's/^URL: /src-gitsvn base /p'))
 BASE_FEED:=$(if $(BASE_FEED),$(BASE_FEED),$(shell cd $(TOPDIR); LC_ALL=C svn info 2>/dev/null | sed -ne 's/^URL: /src-svn base /p'))
-BASE_FEED:=$(if $(BASE_FEED),$(BASE_FEED),src-git base https://git.lede-project.org/source.git$(if $(GIT_BRANCH),;$(GIT_BRANCH)))
+BASE_FEED:=$(if $(BASE_FEED),$(BASE_FEED),src-git base https://git.lede-project.org/source.git$(if $(GIT_BRANCH),;$(GIT_BRANCH),$(if $(GIT_TAGNAME),;$(GIT_TAGNAME))))
 
 KDIR_BASE = $(patsubst $(TOPDIR)/%,%,$(LINUX_DIR))