[U-Boot] [OpenQuestion] stdint.h and inttypes.h in U-Boot ?
Masahiro YAMADA
yamada.m at jp.panasonic.com
Tue Dec 16 02:47:48 CET 2014
Simon,
2014-12-02 5:06 GMT+09:00 Simon Glass <sjg at chromium.org>:
> Hi Masahiro,
>
> On 26 November 2014 at 00:45, Masahiro Yamada <yamada.m at jp.panasonic.com> wrote:
>> Hi Tom, Simon, other developers,
>>
>>
>>
>> Since commit 0d296cc2d3b8 (Provide option to avoid defining a custom version of uintptr_t)
>> and commit 4166ecb247a1 (Add some standard headers external code might need),
>> I have been wondering if they were right decisions.
>>
>>
>>
>> As arch/arm/include/asm/types.h of Linux Kernel says,
>> using 'stdint.h' is not feasible.
>>
>> -------------------------------------->8-------------------------------------
>> /*
>> * The C99 types uintXX_t that are usually defined in 'stdint.h' are not as
>> * unambiguous on ARM as you would expect. For the types below, there is a
>> * difference on ARM between GCC built for bare metal ARM, GCC built for glibc
>> * and the kernel itself, which results in build errors if you try to build with
>> * -ffreestanding and include 'stdint.h' (such as when you include 'arm_neon.h'
>> * in order to use NEON intrinsics)
>> *
>> * As the typedefs for these types in 'stdint.h' are based on builtin defines
>> * supplied by GCC, we can tweak these to align with the kernel's idea of those
>> * types, so 'linux/types.h' and 'stdint.h' can be safely included from the same
>> * source file (provided that -ffreestanding is used).
>> *
>> * int32_t uint32_t uintptr_t
>> * bare metal GCC long unsigned long unsigned int
>> * glibc GCC int unsigned int unsigned int
>> * kernel int unsigned int unsigned long
>> */
>> --------------------------------------8<----------------------------------------
>>
>
> To me this doesn't matter. I feel that int32_t should probably be int
> on 32-bit ARM, but actually so long as it is consistent then it is
> fine if it is long. In fact so long as these types are defined
> consistently, everything works.
Gabe Black and you broke the consistency.
See my explanation below.
>>
>> Actually, the kernel never includes <stdint.h> except host programs.
>>
>>
>> Commit 0d296cc2d3b8 introduced "USE_STDINT", but it causes type conflicts
>> depending on which GCC is used.
>>
>>
>> With ARM bare metal GCC,
>>
>> yamada at beagle:~/workspace/u-boot$ make omap3_beagle_defconfig all CROSS_COMPILE=arm-none-eabi- USE_STDINT=1
>> #
>> # configuration written to .config
>> #
>> #
>> # configuration written to spl/.config
>> #
>> scripts/kconfig/conf --silentoldconfig Kconfig
>> scripts/kconfig/conf --silentoldconfig Kconfig
>> CHK include/config.h
>> GEN include/autoconf.mk
>> GEN include/autoconf.mk.dep
>> GEN spl/include/autoconf.mk
>> CHK include/config/uboot.release
>> CHK include/generated/version_autogenerated.h
>> CHK include/generated/timestamp_autogenerated.h
>> UPD include/generated/timestamp_autogenerated.h
>> CC lib/asm-offsets.s
>> In file included from /opt/arm-2011.03/bin/../lib/gcc/arm-none-eabi/4.5.2/include/stdint.h:5:0,
>> from include/compiler.h:117,
>> from include/image.h:19,
>> from include/common.h:85,
>> from lib/asm-offsets.c:15:
>> /opt/arm-2011.03/bin/../lib/gcc/arm-none-eabi/4.5.2/include/stdint-gcc.h:40:24: error: conflicting types for 'int32_t'
>> include/linux/types.h:99:17: note: previous declaration of 'int32_t' was here
>> /opt/arm-2011.03/bin/../lib/gcc/arm-none-eabi/4.5.2/include/stdint-gcc.h:52:25: error: conflicting types for 'uint32_t'
>> include/linux/types.h:105:17: note: previous declaration of 'uint32_t' was here
>> make[2]: *** [lib/asm-offsets.s] Error 1
>> make[1]: *** [prepare0] Error 2
>> make: *** [__build_one_by_one] Error 2
>>
>>
>
> While toolchain is this? I don't see this problem - it seems broken.
Not broken at all.
I downloaded it from Mentor Graphics
http://www.mentor.com/embedded-software/codesourcery
This is a bare-metal compiler.
If you do not understand, you should read arch/arm/include/asm/types.h
of Linux Kernel once again.
Until commit 0d296cc2d, U-Boot has used the hard-coded defines like Linux.
In my understaing, we should only use ILP32 and LP64 compilers.
short int long longlong pointer
ILP32 (32bit system) 16 32 32 64 32
LP64 (64bit Unix-like system) 16 32 64 64 64
Whether it is 32bit or 64bit system, we can hard-code
u32/uint32_t as unsigned int
u64/uint64_t as unsigned long long
uintptr_t as unsigned long
We do not need to refer to compiler-provided headers.
Moreover, we __should not__ refer to compiler-provided <stdint.h>.
Including <stdint.h> means that we use uint32_t defined by the compiler.
It is "unsigned int" on some compilers, and "unsigned long" on
some compilers.
We still have the hard-coded uint32_t define in <linux/types.h>
This causes the type conflict error I showed above.
OK, we can fix it, but horrible problems still remain.
If we depends on <stdint.h>, we do not know if uint32_t is defined
as "unsigned int" or "unsigned long".
To print out 32bit variables, we would always have to use PRId32.
Do you want to modify all the printf() printing 32bit variables
just to make them unreadable?
>> OK, we can fix "int32_t" and "uint32_t", but it still seems strange to see that
>> "uint32_t" is defined as "unsigned long", whereas "u32" is defined as "unsigned int".
>>
>> If so, must we fix "u32", "s32", ... all the fixed-width typedefs ?
>>
>> I notice including <linux/types.h> in the U-Boot source tree and
>> <stdint.h> provided by your compiler at the same time is a nightmare.
>>
>> If we lean toward <stdint.h>, we must ban <linux/types.h>,
>> but <stdint.h> is not available all the time.
>> For example, kernel.org tool-chains do not provide <stdint.h>.
>>
>> Maybe we can drastically re-write <linux/types.h> and friends
>> to resolve the type conflicts, but I do not think we should not drift apart from the kernel
>> because we have borrowed many source files from Linux.
>
> So far I don't see a big problem.
Horrible problem!
> I feel that, were stdint.h available
> earlier, then types.h might not have been written and we would just
> use stdint.h. Presumably stdint.h has been created to fix these sorts
> of problems, and in fact for new projects, they would not define their
> own types.
What is missing is how to pass the variable width nicely to printf()/scanf().
printf("foo =" PRId32 "\n", foo_32);
printf("bar =" PRId64 "\n", bar_64);
This is ridiculous. Extremely unreadable.
I want something like this:
printf("foo = %32x \n", foo_32);
printf("bar =" %64x \n", bar_64);
If this had been provided, Linux and U-Boot might have adopted <stdint.h>,
but in fact, PRI* is an awful workaround.
> IMO in time the kernel and U-Boot might move to stdint.h, and having
> it as an option at the moment helps us understand the issues. It does
> not break any builds.
I double it.
Using <stdint.h> is a misjudge. It will mess up printf() everywhere.
Linux Kernel has guideline how to print each variable type.
Documentation/printk-formats.txt
> I could be wrong though, time will tell. We should keep an eye on it.
If we keep wrong code in the code base, someone might continue development
base on it, which is also wrong.
In order not to lose our time, wrong code should be immediately removed.
--
Best Regards
Masahiro Yamada
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