Re: [Qemu-devel] [PATCH 5/6] Remove warning in printf due to type mismatch

[Markus Armbruster]

Stefan Weil <address@hidden> writes:

> Am 27.05.2011 19:22, schrieb Alexandre Raymond:
>> ----8<----
>> qemu/target-lm32/translate.c: In function
>> ‘gen_intermediate_code_internal’:
>> qemu/target-lm32/translate.c:1135: warning: format ‘%zd’ expects
>> type ‘signed size_t’, but argument 4 has type ‘int’
>> ----8<----
>>
>> Both gen_opc_ptr and gen_opc_buf are "uint16_t *", so a simple '%d' should
>> be able to describe their relative difference.
>>
>> Signed-off-by: Alexandre Raymond <address@hidden>
>> ---
>> target-lm32/translate.c | 2 +-
>> 1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/target-lm32/translate.c b/target-lm32/translate.c
>> index eb21158..0f69f27 100644
>> --- a/target-lm32/translate.c
>> +++ b/target-lm32/translate.c
>> @@ -1132,7 +1132,7 @@ static void
>> gen_intermediate_code_internal(CPUState *env,
>> if (qemu_loglevel_mask(CPU_LOG_TB_IN_ASM)) {
>> qemu_log("\n");
>> log_target_disas(pc_start, dc->pc - pc_start, 0);
>> - qemu_log("\nisize=%d osize=%zd\n",
>> + qemu_log("\nisize=%d osize=%d\n",
>> dc->pc - pc_start, gen_opc_ptr - gen_opc_buf);
>> }
>> #endif
>
> Nack.
>
> The original code is correct, because the difference of two pointers
> is always of type ssize_t (well, obviously not with your compiler,
> but then I assume that your compiler is broken).

ISO/IEC 9899:1999 §6.5.6 on pointer subtraction:

    The size of the result is implementation-defined, and its type (a
    signed integer type) is ptrdiff_t defined in the <stddef.h> header.

The pedantically correct way to print a pointer difference is the 't'
type modifier.  Ibid. §7.19.6.1 on fprintf():

    t   Specifies  that a following d, i, o, u, x, or X conversion
        specifier applies to a ptrdiff_t or the corresponding unsigned
        integer type argument; or that a following n conversion
        specifier applies to a pointer to a ptrdiff_t argument.

ssize_t is POSIX, not ISO C.  It can differ from ptrdiff_t only if
ptrdiff_t has a different size than size_t, which would be kind of sick.
ISO C permits all kinds of sickness.  Whether tolerating a particular
sickness is worth our while is another question.

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