What to do when size of the struct differs on 32 and 64 bit?

[Anssi Hannula]

Marcus Meissner wrote:
> On Tue, Aug 12, 2008 at 11:44:20PM -0600, Vitaliy Margolen wrote:
>> While debugging some force-feedback issues ran into an interesting problem. 
>> The size of one struct from include/linux differs between 32-bit and 64-bit. 
>> That wouldn't be a major problem except that size is the part of the ioctl() 
>> request. Which results in EINVAL.
>>
>> In more details:
>> input.h:
>> #define EVIOCSFF _IOC(_IOC_WRITE, 'E', 0x80, sizeof(struct ff_effect))
>>
>> The simple test program:
>>
>> #include <linux/input.h>
>> #include <stdio.h>
>> int main(int argc, char * argv[])
>> {
>>      printf("sizeof(struct ff_effect) = %d EVIOCSFF=%#x\n", sizeof(struct 
>> ff_effect), EVIOCSFF);
>>
>>      return 0;
>> }
>>
>>
>> $ gcc test_size.c -o test_size && ./test_size
>> sizeof(struct ff_effect) = 48 EVIOCSFF=0x40304580
>> $ gcc -m32 test_size.c -o test_size32 && ./test_size32
>> sizeof(struct ff_effect) = 44 EVIOCSFF=0x402c4580
>>
>> The question is what do we do about it? I'm sure there are might be more 
>> cases like that.
> 
> The kernel is supposed to handle this transparently.
> 
> I would report this to the kernel developers, mention "32bit compatibility"
> or so.

Just for the record, it has been fixed for 2.6.27:
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=f2278f31d6feb9036eaa79f2e8abcce850420abd

-- 
Anssi Hannula