Re: [PATCH 1/1] Makefile: only use compiler flags when supported

[Simon Glass <sjg@chromium.org>]

Hi Markus,

On Tue, 8 Oct 2024 at 15:42, Markus Mayer <mmayer@broadcom.com> wrote:
>
> We need to check if some compiler flags are supported as not all
> compilers may do so. For instance, "-Wsuggest-attribute=format" is
> supported by gcc but not by clang.
>
> Using a compiler option that is not supported will most likely cause the
> build to fail, since we are building with "-Werror" and the compiler will
> issue a warning about the unknown option.
>
> As a result, we only use the option if the compiler understands it.
>
> Signed-off-by: Markus Mayer <mmayer@broadcom.com>
> ---
>  Makefile | 25 ++++++++++++++++++++++++-
>  1 file changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/Makefile b/Makefile
> index f1f0ab368cd3..febdca5742c5 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -3,6 +3,26 @@
>  # Device Tree Compiler
>  #
>
> +# try-run and cc-option were stolen from the Linux kernel
> +TMPOUT = .tmp_$$$$
> +# try-run
> +# Usage: option = $(call try-run, $(CC)...-o "$$TMP",option-ok,otherwise)
> +# Exit code chooses option. "$$TMP" serves as a temporary file and is
> +# automatically cleaned up.
> +try-run = $(shell set -e;              \
> +       TMP=$(TMPOUT)/tmp;              \
> +       mkdir -p $(TMPOUT);             \
> +       trap "rm -rf $(TMPOUT)" EXIT;   \
> +       if ($(1)) >/dev/null 2>&1;      \
> +       then echo "$(2)";               \
> +       else echo "$(3)";               \
> +       fi)
> +
> +# cc-option
> +# Usage: cflags-y += $(call cc-option,-march=winchip-c6,-march=i586)
> +cc-option = $(call try-run, \
> +       $(CC) -Werror $(1) -c -x c /dev/null -o "$$TMP",$(1),$(2))
> +
>  #
>  # Version information will be constructed in this order:
>  # DTC_VERSION release version as MAJOR.MINOR.PATCH
> @@ -18,9 +38,12 @@ CONFIG_LOCALVERSION =
>  ASSUME_MASK ?= 0
>
>  CPPFLAGS = -I libfdt -I . -DFDT_ASSUME_MASK=$(ASSUME_MASK)
> +# Warnings where we need to check they are supported
> +OPT_WARNINGS = $(call cc-option,-Wsuggest-attribute=format)

This is fine, but you should be able to use the existing cc-option in U-Boot

> +# Regular warnings
>  WARNINGS = -Wall -Wpointer-arith -Wcast-qual -Wnested-externs -Wsign-compare \
>         -Wstrict-prototypes -Wmissing-prototypes -Wredundant-decls -Wshadow \
> -       -Wsuggest-attribute=format -Wwrite-strings
> +       -Wwrite-strings $(OPT_WARNINGS)
>  CFLAGS = -g -Os $(SHAREDLIB_CFLAGS) -Werror $(WARNINGS) $(EXTRA_CFLAGS)
>
>  BISON = bison
> --
> 2.46.0
>
>

Regards,
Simon