Re: [Qemu-devel] [PATCH] tpm_tis: fix format for 64bit variable

[Eric Blake <eblake@redhat.com>]

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On 03/31/2015 08:09 AM, Eric Blake wrote:
> On 03/31/2015 07:27 AM, Stefan Berger wrote:
>> Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
>> ---
>>  hw/tpm/tpm_tis.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/hw/tpm/tpm_tis.c b/hw/tpm/tpm_tis.c
>> index 815c8ea..52e0148 100644
>> --- a/hw/tpm/tpm_tis.c
>> +++ b/hw/tpm/tpm_tis.c
>> @@ -814,7 +814,7 @@ static void tpm_tis_mmio_write_intern(void *opaque, hwaddr addr,
>>              tis->loc[locty].state == TPM_TIS_STATE_COMPLETION) {
>>              /* drop the byte */
>>          } else {
>> -            DPRINTF("tpm_tis: Data to send to TPM: %08x (size=%d)\n",
>> +            DPRINTF("tpm_tis: Data to send to TPM: %08lx (size=%d)\n",
> 
> NACK.  When printing uint64_t val, you HAVE to use PRIx64, not lx, for
> the sake of 32-bit platforms.

Furthermore, you could have caught this much sooner if you fix the
definition of DPRINTF.  This file used:

#ifdef DEBUG_TIS
#define DPRINTF(fmt, ...) \
    do { fprintf(stderr, fmt, ## __VA_ARGS__); } while (0)
#else
#define DPRINTF(fmt, ...) \
    do { } while (0)
#endif

which is bad, because the compiler CAN'T see the type mismatch unless
you turn debugging on (alas, we have a LOT of files in the code base
with similar bad patterns).  A better example is hw/display/cg3.c:

/* Change to 1 to enable debugging */
#define DEBUG_CG3 0
...
#define DPRINTF(fmt, ...) do { \
    if (DEBUG_CG3) { \
        printf("CG3: " fmt , ## __VA_ARGS__); \
    } \
} while (0);

where now the compiler can unconditionally do -Wformat checking and
avoid bit-rot, even if debug printing is never turned on, and without
penalizing code size when debugging is off.


-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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