[U-Boot] [RFC] C2011 standard for building U-Boot
xypron.glpk at gmx.de
Fri Aug 4 15:58:53 UTC 2017
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 ($(HOSTOS),cygwin)
>>> HOSTCFLAGS += -ansi
>>> # Xtensa linker script cannot be preprocessed with -ansi because of
>>> # preprocessor operations on strings that don't make C identifiers.
>>> ifeq ($(CONFIG_XTENSA),)
>>> LDPPFLAGS += -ansi
>>> # Create a file containing the configuration options the image was built
>>> 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
>>> 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
>>> 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.. maybe 4.7 or even v4.6 is
> complete enough for what we need.. that seems plenty old enough. I'm
> less familiar with clang but wikipedia says 3.1.
> If some board/arch was stuck on something older, I guess we could make
> it a kconfig option that EFI_LOADER depends on.
>  https://gcc.gnu.org/wiki/C11Status
>  https://en.wikipedia.org/wiki/C11_(C_standard_revision)
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.
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