[RFC PATCH] selftests: introduce and use SELFTESTS_CC_IS_CLANG instead of LLVM

[John Hubbard <jhubbard@nvidia.com>]

Current practice in the selftests Makefiles is to use $(LLVM) as a way
to decide if clang is being used as the compiler (and/or the linker
front end). Unfortunately, this does not cover all of the use cases:

1) CC could have been set within selftests/lib.mk, by inferring it from
LLVM==1, or

2) CC could have been set externally, such as when cross compiling.

Solution: In order to allow subsystem selftests to more accurately
control clang-specific behavior, such as compiler options, provide a new
Makefile variable: SELFTESTS_CC_IS_CLANG. If $(CC) contains an
invocation of clang in any form, then SELFTESTS_CC_IS_CLANG will be
non-empty.

SELFTESTS_CC_IS_CLANG does not specify which linker is being used.
However, it can still help with linker options, because $(CC) is often
used to do both the compile and link steps (often in the same step).

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---

Hi,

If this looks reasonable, I'll break it up into separate patches and
post it as a non-RFC.

thanks,
John Hubbard

 tools/testing/selftests/bpf/Makefile       |  2 +-
 tools/testing/selftests/fchmodat2/Makefile | 12 +++++++-----
 tools/testing/selftests/hid/Makefile       |  2 +-
 tools/testing/selftests/lib.mk             | 15 +++++++++++++++
 tools/testing/selftests/openat2/Makefile   | 16 +++++++++-------
 5 files changed, 33 insertions(+), 14 deletions(-)

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index dd49c1d23a60..6b924297ab71 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -55,7 +55,7 @@ progs/test_sk_lookup.c-CFLAGS := -fno-strict-aliasing
 progs/timer_crash.c-CFLAGS := -fno-strict-aliasing
 progs/test_global_func9.c-CFLAGS := -fno-strict-aliasing
 
-ifneq ($(LLVM),)
+ifeq ($(SELFTESTS_CC_IS_CLANG),)
 # Silence some warnings when compiled with clang
 CFLAGS += -Wno-unused-command-line-argument
 endif
diff --git a/tools/testing/selftests/fchmodat2/Makefile b/tools/testing/selftests/fchmodat2/Makefile
index 4373cea79b79..d00b01be5d96 100644
--- a/tools/testing/selftests/fchmodat2/Makefile
+++ b/tools/testing/selftests/fchmodat2/Makefile
@@ -2,14 +2,16 @@
 
 CFLAGS += -Wall -O2 -g -fsanitize=address -fsanitize=undefined $(KHDR_INCLUDES)
 
+TEST_GEN_PROGS := fchmodat2_test
+
+include ../lib.mk
+
 # gcc requires -static-libasan in order to ensure that Address Sanitizer's
 # library is the first one loaded. However, clang already statically links the
 # Address Sanitizer if -fsanitize is specified. Therefore, simply omit
 # -static-libasan for clang builds.
-ifeq ($(LLVM),)
+# This check must be done after including ../lib.mk, in order to pick up the
+# correct value of SELFTESTS_CC_IS_CLANG.
+ifeq ($(SELFTESTS_CC_IS_CLANG),)
     CFLAGS += -static-libasan
 endif
-
-TEST_GEN_PROGS := fchmodat2_test
-
-include ../lib.mk
diff --git a/tools/testing/selftests/hid/Makefile b/tools/testing/selftests/hid/Makefile
index 2b5ea18bde38..734a53dc8ad9 100644
--- a/tools/testing/selftests/hid/Makefile
+++ b/tools/testing/selftests/hid/Makefile
@@ -27,7 +27,7 @@ CFLAGS += -I$(OUTPUT)/tools/include
 LDLIBS += -lelf -lz -lrt -lpthread
 
 # Silence some warnings when compiled with clang
-ifneq ($(LLVM),)
+ifeq ($(SELFTESTS_CC_IS_CLANG),)
 CFLAGS += -Wno-unused-command-line-argument
 endif
 
diff --git a/tools/testing/selftests/lib.mk b/tools/testing/selftests/lib.mk
index 429535816dbd..f321ad5a1d0c 100644
--- a/tools/testing/selftests/lib.mk
+++ b/tools/testing/selftests/lib.mk
@@ -43,6 +43,21 @@ else
 CC := $(CROSS_COMPILE)gcc
 endif # LLVM
 
+# SELFTESTS_CC_IS_CLANG allows subsystem selftests to more accurately control
+# clang-specific behavior, such as compiler options. If CC is an invocation of
+# clang in any form, then SELFTESTS_CC_IS_CLANG will be non-empty. Notes:
+#
+# 1) CC could have been set above, by inferring it from LLVM==1, or externally,
+# from the CC shell environment variable.
+#
+# 2) SELFTESTS_CC_IS_CLANG does not specify which linker is being used. However,
+#    it can still help with linker options, if clang or gcc is used for the
+#    linker front end.
+SELFTESTS_CC_IS_CLANG :=
+ifeq ($(findstring clang,$(CC)),clang)
+    SELFTESTS_CC_IS_CLANG := 1
+endif
+
 ifeq (0,$(MAKELEVEL))
     ifeq ($(OUTPUT),)
 	OUTPUT := $(shell pwd)
diff --git a/tools/testing/selftests/openat2/Makefile b/tools/testing/selftests/openat2/Makefile
index 185dc76ebb5f..7acb85a8f2ac 100644
--- a/tools/testing/selftests/openat2/Makefile
+++ b/tools/testing/selftests/openat2/Makefile
@@ -3,16 +3,18 @@
 CFLAGS += -Wall -O2 -g -fsanitize=address -fsanitize=undefined
 TEST_GEN_PROGS := openat2_test resolve_test rename_attack_test
 
+LOCAL_HDRS += helpers.h
+
+include ../lib.mk
+
+$(TEST_GEN_PROGS): helpers.c
+
 # gcc requires -static-libasan in order to ensure that Address Sanitizer's
 # library is the first one loaded. However, clang already statically links the
 # Address Sanitizer if -fsanitize is specified. Therefore, simply omit
 # -static-libasan for clang builds.
-ifeq ($(LLVM),)
+# This check must be done after including ../lib.mk, in order to pick up the
+# correct value of SELFTESTS_CC_IS_CLANG.
+ifeq ($(SELFTESTS_CC_IS_CLANG),)
     CFLAGS += -static-libasan
 endif
-
-LOCAL_HDRS += helpers.h
-
-include ../lib.mk
-
-$(TEST_GEN_PROGS): helpers.c

base-commit: 9a5cd459be8a425d70cda1fa1c89af7875a35d17
-- 
2.45.2