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Since commit 031dbb1224 ("AArch32: Add essential Arch helpers"),
it is difficult to use consistent format strings for printf() family
between aarch32 and aarch64.
For example, uint64_t is defined as 'unsigned long long' for aarch32
and as 'unsigned long' for aarch64. Likewise, uintptr_t is defined
as 'unsigned int' for aarch32, and as 'unsigned long' for aarch64.
A problem typically arises when you use printf() in common code.
One solution could be, to cast the arguments to a type long enough
for both architectures. For example, if 'val' is uint64_t type,
like this:
printf("val = %llx\n", (unsigned long long)val);
Or, somebody may suggest to use a macro provided by <inttypes.h>,
like this:
printf("val = %" PRIx64 "\n", val);
But, both would make the code ugly.
The solution adopted in Linux kernel is to use the same typedefs for
all architectures. The fixed integer types in the kernel-space have
been unified into int-ll64, like follows:
typedef signed char int8_t;
typedef unsigned char uint8_t;
typedef signed short int16_t;
typedef unsigned short uint16_t;
typedef signed int int32_t;
typedef unsigned int uint32_t;
typedef signed long long int64_t;
typedef unsigned long long uint64_t;
[ Linux commit: 0c79a8e29b5fcbcbfd611daf9d500cfad8370fcf ]
This gets along with the codebase shared between 32 bit and 64 bit,
with the data model called ILP32, LP64, respectively.
The width for primitive types is defined as follows:
ILP32 LP64
int 32 32
long 32 64
long long 64 64
pointer 32 64
'long long' is 64 bit for both, so it is used for defining uint64_t.
'long' has the same width as pointer, so for uintptr_t.
We still need an ifdef conditional for (s)size_t.
All 64 bit architectures use "unsigned long" size_t, and most 32 bit
architectures use "unsigned int" size_t. H8/300, S/390 are known as
exceptions; they use "unsigned long" size_t despite their architecture
is 32 bit.
One idea for simplification might be to define size_t as 'unsigned long'
across architectures, then forbid the use of "%z" string format.
However, this would cause a distortion between size_t and sizeof()
operator. We have unknowledge about the native type of sizeof(), so
we need a guess of it anyway. I want the following formula to always
return 1:
__builtin_types_compatible_p(size_t, typeof(sizeof(int)))
Fortunately, ARM is probably a majority case. As far as I know, all
32 bit ARM compilers use "unsigned int" size_t.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
pull/1255/head
Masahiro Yamada
7 years ago
9 changed files with 36 additions and 55 deletions
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