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Subject: Re: [BlueZ PATCH] lib: fix variable-length array declarations in hci
 structures
To:     Marcel Holtmann <marcel@holtmann.org>
Cc:     linux-bluetooth@vger.kernel.org
References: <20210831163545.3646157-1-pab@pabigot.com>
 <3CBFA8E8-ABA1-495F-BFD4-A4E3CBC1E21B@holtmann.org>
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On 8/31/21 2:23 PM, Marcel Holtmann wrote:
> Hi Peter,
>
>> Use of zero as the size for arrays as the last element of a structure
>> is a GNU C extension, which as of GCC 10 produces diagnostics when
>> values in the extended array are referenced.  Switch to the C99
>> standard idiom for flexible array members, already in use in a few
>> other headers.
>>
>> Signed-off-by: Peter A. Bigot <pab@pabigot.com>
>> ---
>>
>> No changes from previous submission except the BlueZ subject prefix
>> that I hope will get this into bluez.
>>
>> lib/hci.h | 16 ++++++++--------
>> 1 file changed, 8 insertions(+), 8 deletions(-)
>>
>> diff --git a/lib/hci.h b/lib/hci.h
>> index 3382b87bf..a61568bce 100644
>> --- a/lib/hci.h
>> +++ b/lib/hci.h
>> @@ -729,7 +729,7 @@ typedef struct {
>> typedef struct {
>> 	uint8_t		flt_type;
>> 	uint8_t		cond_type;
>> -	uint8_t		condition[0];
>> +	uint8_t		condition[];
>> } __attribute__ ((packed)) set_event_flt_cp;
>> #define SET_EVENT_FLT_CP_SIZE 2
> does this break any API assumptions? Since as long as libbluetooth exists these headers are API.

The size of the structure remains the same; there should be no API
changes.  I've done this sort of change multiple times over the years
and nobody's reported any problems.

Peter