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

[Heinrich Schuchardt]

On 08/04/2017 03:53 PM, Rob Clark wrote:
> 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
> 

Since gcc 4.7 the option -std=c11 is available.
Since gcc 6.1 the default is -std=gnu11 (C2011 + gnu extensions)
Cygwin provides gcc 6.3.

Clang 2.9 has C11 suppport selected by -std=c11.
Since Clang 3.6 switch to C11 by default.

If it is compatible with the code base I think the best would be to
explicitly set -std=c11.

I will prepare a patch and test with Travis CI.

Best regards

Heinrich