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

[Rob Clark]

On Fri, Aug 4, 2017 at 9:20 AM, Tom Rini <trini at konsulko.com> wrote:
> 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!
>

It looks like probably gcc 4.9[1].. maybe 4.7 or even v4.6[2] is
complete enough for what we need.. that seems plenty old enough.  I'm
less familiar with clang but wikipedia says 3.1[2].

If some board/arch was stuck on something older, I guess we could make
it a kconfig option that EFI_LOADER depends on.

[1] https://gcc.gnu.org/wiki/C11Status
[2] https://en.wikipedia.org/wiki/C11_(C_standard_revision)

BR,
-R