[U-Boot] [RFC] C2011 standard for building U-Boot

[Tom Rini]

On Thu, Aug 03, 2017 at 06:27:02AM +0200, Heinrich Schuchardt wrote:
> Hello Tom,
> 
> for the UEFI implementation of U-Boot it would make defining string
> constants much easier using the following C 2011 notation:
> 
> u16 *foo = u"My lovely string";
> 
> Do you see any reason forcing us not to use features of C 2011?
> 
> In /Makefile I found the following:
> 
> ifeq ($(HOSTOS),cygwin)
> HOSTCFLAGS      += -ansi
> endif
> 
> #
> # Xtensa linker script cannot be preprocessed with -ansi because of
> # preprocessor operations on strings that don't make C identifiers.
> #
> ifeq ($(CONFIG_XTENSA),)
> LDPPFLAGS       += -ansi
> endif
> 
> # Create a file containing the configuration options the image was built
> with
> quiet_cmd_cpp_cfg = CFG     $@
> cmd_cpp_cfg = $(CPP) -Wp,-MD,$(depfile) $(cpp_flags) $(LDPPFLAGS) -ansi \
> -DDO_DEPS_ONLY -D__ASSEMBLY__ -x assembler-with-cpp -P -dM -E -o $@ $<
> 
> The GCC documentation teaches:
> -ansi: In C mode, this is equivalent to -std=c90. In C++ mode, it is
> equivalent to -std=c++98.
> 
> When I am building for arm64 I find these options actually used:
> 
>   aarch64-linux-gnu-gcc -Wp,-MD,common/.cli_hush.o.d  -nostdinc -isystem
> /usr/lib/gcc-cross/aarch64-linux-gnu/6/include -Iinclude
> -I./arch/arm/include -include ./include/linux/kconfig.h -D__KERNEL__
> -D__UBOOT__ -Wall -Wstrict-prototypes -Wno-format-security -fno-builtin
> -ffreestanding -Os -fno-stack-protector -fno-delete-null-pointer-checks
> -g -fstack-usage -Wno-format-nonliteral -Werror=date-time -D__ARM__
> -fno-pic -mstrict-align -ffunction-sections -fdata-sections -fno-common
> -ffixed-r9 -fno-common -ffixed-x18 -pipe -march=armv8-a
> -D__LINUX_ARM_ARCH__=8 -I./arch/arm/mach-meson/include
> -D"KBUILD_STR(s)=#s" -D"KBUILD_BASENAME=KBUILD_STR(cli_hush)"
> -D"KBUILD_MODNAME=KBUILD_STR(cli_hush)" -c -o common/cli_hush.o
> common/cli_hush.c
> 
> My impression is that:
> 
> We have variables in /Makefile that are not used for anything:
> LDPPFLAGS, cmd_cpp_cfg, cmd_cpp_lds.
> 
> All lines refering to these variables should be removed.
> Cf. https://lists.denx.de/pipermail/u-boot/2016-September/267177.html

OK.  Drop 'em, throw travis-ci at it and see what, if anything, blows
up.

> We force C90 on cygwin to compile the host code but not for the actual
> U-Boot code. Probably a remnant from a distant past.
> 
> So nothing should stop us from using C2011 in U-Boot.

What's the minimum gcc (and llvm) version we need to use here?  Thanks!

-- 
Tom
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