From: Shuah Khan <skhan@linuxfoundation.org>

[ Upstream commit 55d554f5d14071f7c2c5dbd88d0a2eb695c97d16 ]

make TARGETS=bpf kselftest fails with:

Makefile:127: tools/build/Makefile.include: No such file or directory

When the bpf tool make is invoked from tools Makefile, srctree is
cleared and the current logic check for srctree equals to empty
string to determine srctree location from CURDIR.

When the build in invoked from selftests/bpf Makefile, the srctree
is set to "." and the same logic used for srctree equals to empty is
needed to determine srctree.

Check building_out_of_srctree undefined as the condition for both
cases to fix "make TARGETS=bpf kselftest" build failure.

Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <redacted>
Link: https://lore.kernel.org/bpf/20190927011344.4695-1-skhan@linuxfoundation.org (local)
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 tools/bpf/Makefile     | 6 +++++-
 tools/lib/bpf/Makefile | 6 +++++-
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/tools/bpf/Makefile b/tools/bpf/Makefile
index 53b60ad452f5d..93a84965345dc 100644
--- a/tools/bpf/Makefile
+++ b/tools/bpf/Makefile

@@ -12,7 +12,11 @@ INSTALL ?= install
 CFLAGS += -Wall -O2
 CFLAGS += -D__EXPORTED_HEADERS__ -I$(srctree)/include/uapi -I$(srctree)/include
 
-ifeq ($(srctree),)
+# This will work when bpf is built in tools env. where srctree
+# isn't set and when invoked from selftests build, where srctree
+# is set to ".". building_out_of_srctree is undefined for in srctree
+# builds
+ifndef building_out_of_srctree
 srctree := $(patsubst %/,%,$(dir $(CURDIR)))
 srctree := $(patsubst %/,%,$(dir $(srctree)))
 endif

diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
index 3624557550a1f..5cd2786cc437c 100644
--- a/tools/lib/bpf/Makefile
+++ b/tools/lib/bpf/Makefile

@@ -7,7 +7,11 @@ BPF_EXTRAVERSION = 1
 
 MAKEFLAGS += --no-print-directory
 
-ifeq ($(srctree),)
+# This will work when bpf is built in tools env. where srctree
+# isn't set and when invoked from selftests build, where srctree
+# is a ".". building_out_of_srctree is undefined for in srctree
+# builds
+ifndef building_out_of_srctree
 srctree := $(patsubst %/,%,$(dir $(CURDIR)))
 srctree := $(patsubst %/,%,$(dir $(srctree)))
 srctree := $(patsubst %/,%,$(dir $(srctree)))

-- 
2.20.1