[Buildroot] [PATCH 1/1] Makefile: Correctly take source date from commit date

[James Byrne]

For reproducible builds SOURCE_DATE_EPOCH is supposed to be set to the
date of the last Buildroot commit if running from a git repository, but
this doesn't actually work. This corrects this in the following way:

1) Set GIT from BR2_GIT, otherwise it may be undefined.

2) Use 'git rev-parse --is-inside-work-tree' to see if we are inside a
Git repository. There is no need to use TOPDIR, because the current
directory will always be TOPDIR, and in any case the Git repository may
be at a higher directory level if Buildroot has been imported into a
larger build system.

Signed-off-by: James Byrne <james.byrne at origamienergy.com>
---
 Makefile | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index 9e2402d..59af554 100644
--- a/Makefile
+++ b/Makefile
@@ -253,8 +253,10 @@ export TZ = UTC
 export LANG = C
 export LC_ALL = C
 export GZIP = -n
-BR2_VERSION_GIT_EPOCH = $(shell GIT_DIR=$(TOPDIR)/.git $(GIT) log -1 --format=%at)
-export SOURCE_DATE_EPOCH ?= $(if $(wildcard $(TOPDIR)/.git),$(BR2_VERSION_GIT_EPOCH),$(BR2_VERSION_EPOCH))
+GIT := $(call qstrip,$(BR2_GIT))
+BR2_IN_WORK_TREE = $(if $(subst false,,$(shell $(GIT) rev-parse --is-inside-work-tree 2> /dev/null || echo false)),Y,)
+BR2_VERSION_GIT_EPOCH = $(shell $(GIT) log -1 --format=%at)
+export SOURCE_DATE_EPOCH ?= $(if $(BR2_IN_WORK_TREE),$(BR2_VERSION_GIT_EPOCH),$(BR2_VERSION_EPOCH))
 endif

 # To put more focus on warnings, be less verbose as default
--
2.7.4

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