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

[John Hubbard <jhubbard@nvidia.com>]

On 7/3/24 8:04 PM, John Hubbard wrote:
> 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),)

It looks like I got the polarity of these checks wrong, after all. sigh :)

>   # 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

thanks,
-- 
John Hubbard
NVIDIA