Re: [Qemu-devel] [PATCH 23/25] fdc: Move floppy geometry guessing back from block.c

[Kevin Wolf <kwolf@redhat.com>]

Am 09.07.2012 17:01, schrieb Anthony Liguori:
> On 07/09/2012 09:16 AM, Kevin Wolf wrote:
>> From: Markus Armbruster<armbru@redhat.com>
>>
>> Commit 5bbdbb46 moved it to block.c because "other geometry guessing
>> functions already reside in block.c".  Device-specific functionality
>> should be kept in device code, not the block layer.  Move it back.
>>
>> Disk geometry guessing is still in block.c.  To be moved out in a
>> later patch series.
>>
>> Bonus: the floppy type used in pc_cmos_init() now obviously matches
>> the one in the FDrive.  Before, we relied on
>> bdrv_get_floppy_geometry_hint() picking the same type both in
>> fd_revalidate() and in pc_cmos_init().
>>
>> Signed-off-by: Markus Armbruster<armbru@redhat.com>
>> Signed-off-by: Kevin Wolf<kwolf@redhat.com>

>> diff --git a/hw/pc.c b/hw/pc.c
>> index c7e9ab3..e5e7647 100644
>> --- a/hw/pc.c
>> +++ b/hw/pc.c
>> @@ -335,10 +335,8 @@ void pc_cmos_init(ram_addr_t ram_size, ram_addr_t above_4g_mem_size,
>>                     ISADevice *floppy, BusState *idebus0, BusState *idebus1,
>>                     ISADevice *s)
>>   {
>> -    int val, nb, nb_heads, max_track, last_sect, i;
>> -    FDriveType fd_type[2] = { FDRIVE_DRV_NONE, FDRIVE_DRV_NONE };
>> -    FDriveRate rate;
>> -    BlockDriverState *fd[MAX_FD];
>> +    int val, nb, i;
>> +    FDriveType fd_type[2];
> 
> This results in:
> 
>    CC    i386-softmmu/hw/i386/../pc.o
> /home/anthony/git/qemu/hw/i386/../pc.c: In function ‘pc_cmos_init’:
> /home/anthony/git/qemu/hw/i386/../pc.c:339:16: error: ‘fd_type[1]’ may be used 
> uninitialized in this function [-Werror=uninitialized]
> /home/anthony/git/qemu/hw/i386/../pc.c:339:16: error: ‘fd_type[0]’ may be used 
> uninitialized in this function [-Werror=uninitialized]
> cc1: all warnings being treated as errors
> 
> And GCC is right as:
> 
>>       static pc_cmos_init_late_arg arg;
>>
>>       /* various important CMOS locations needed by PC/Bochs bios */
>> @@ -381,13 +379,8 @@ void pc_cmos_init(ram_addr_t ram_size, ram_addr_t above_4g_mem_size,
>>
>>       /* floppy type */
>>       if (floppy) {
>> -        fdc_get_bs(fd, floppy);
>>           for (i = 0; i<  2; i++) {
>> -            if (fd[i]) {
>> -                bdrv_get_floppy_geometry_hint(fd[i],&nb_heads,&max_track,
>> -&last_sect, FDRIVE_DRV_NONE,
>> -&fd_type[i],&rate);
>> -            }
>> +            fd_type[i] = isa_fdc_get_drive_type(floppy, i);
>>           }
>>       }
>>       val = (cmos_get_fd_drive_type(fd_type[0])<<  4) |
> 
> This is an unconditional use of fd_type[0].  If floppy == NULL, this is 
> dereferencing an uninitialized value.
> 
> I'm not sure why the explicit initialization was removed...

Looks broken indeed. I just wonder why my gcc (or the buildbots) didn't
complain.

I dropped this patch from for-anthony, so you can give the pull request
another try.

Kevin