[PATCH AUTOSEL 5.4 343/350] tools, bpf: Fix build for 'make -s tools/bpf O=<dir>'

[Sasha Levin]

From: Quentin Monnet <quentin.monnet@xxxxxxxxxxxxx>

[ Upstream commit a89b2cbf71d64b61e79bbe5cb7ff4664797eeaaf ]

Building selftests with 'make TARGETS=bpf kselftest' was fixed in commit
55d554f5d140 ("tools: bpf: Use !building_out_of_srctree to determine
srctree"). However, by updating $(srctree) in tools/bpf/Makefile for
in-tree builds only, we leave out the case where we pass an output
directory to build BPF tools, but $(srctree) is not set. This
typically happens for:

    $ make -s tools/bpf O=/tmp/foo
    Makefile:40: /tools/build/Makefile.feature: No such file or directory

Fix it by updating $(srctree) in the Makefile not only for out-of-tree
builds, but also if $(srctree) is empty.

Detected with test_bpftool_build.sh.

Fixes: 55d554f5d140 ("tools: bpf: Use !building_out_of_srctree to determine srctree")
Signed-off-by: Quentin Monnet <quentin.monnet@xxxxxxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Acked-by: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/bpf/20191119105626.21453-1-quentin.monnet@xxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 tools/bpf/Makefile | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/bpf/Makefile b/tools/bpf/Makefile
index 5d1995fd369c6..5535650800ab2 100644
--- a/tools/bpf/Makefile
+++ b/tools/bpf/Makefile
@@ -16,7 +16,13 @@ CFLAGS += -D__EXPORTED_HEADERS__ -I$(srctree)/include/uapi -I$(srctree)/include
 # isn't set and when invoked from selftests build, where srctree
 # is set to ".". building_out_of_srctree is undefined for in srctree
 # builds
+ifeq ($(srctree),)
+update_srctree := 1
+endif
 ifndef building_out_of_srctree
+update_srctree := 1
+endif
+ifeq ($(update_srctree),1)
 srctree := $(patsubst %/,%,$(dir $(CURDIR)))
 srctree := $(patsubst %/,%,$(dir $(srctree)))
 endif
-- 
2.20.1