fallthrough question

fallthrough question

[Randy Dunlap]

Hi,

I expected this to produce a fallthrough warning, but it doesn't
(with gcc 11.1.0):

from sound/oss/dmasound/dmasound_core.c:#1481, when falling from case 1
into case 0: (in arch/m68k/ selected builds only)

	case 1:
		if ((size = ints[2]) < 256) /* check for small buffer specs */
			size <<= 10 ;
                if (size < MIN_BUFSIZE || size > MAX_BUFSIZE)
                        printk("dmasound_setup: invalid write buffer size, using default = %d\n", writeBufSize);
                else
                        writeBufSize = size;
	case 0:
		break;
	default:

Can you tell me what is going on here?

thanks.
-- 
~Randy

Re: fallthrough question

[Gustavo A. R. Silva]

Hi there,

On Fri, Feb 18, 2022 at 01:57:58PM -0800, Randy Dunlap wrote:
> Hi,
> 
> I expected this to produce a fallthrough warning, but it doesn't
> (with gcc 11.1.0):
> 
> from sound/oss/dmasound/dmasound_core.c:#1481, when falling from case 1
> into case 0: (in arch/m68k/ selected builds only)
> 
> 	case 1:
> 		if ((size = ints[2]) < 256) /* check for small buffer specs */
> 			size <<= 10 ;
>                 if (size < MIN_BUFSIZE || size > MAX_BUFSIZE)
>                         printk("dmasound_setup: invalid write buffer size, using default = %d\n", writeBufSize);
>                 else
>                         writeBufSize = size;
> 	case 0:
> 		break;
> 	default:
> 
> Can you tell me what is going on here?

As you can see the warning is suppressed when a case label falls through to
a case that merely breaks... or returns, or continues (continue statement)
or that goes to (goto statement) some other place.

However, Clang disagrees with this. See below for more:

https://github.com/ClangBuiltLinux/linux/issues/636
https://godbolt.org/z/xgkvIh

--
Gustavo

Re: fallthrough question

[Randy Dunlap]

On 2/18/22 15:15, Gustavo A. R. Silva wrote:
> Hi there,
> 
> On Fri, Feb 18, 2022 at 01:57:58PM -0800, Randy Dunlap wrote:
>> Hi,
>>
>> I expected this to produce a fallthrough warning, but it doesn't
>> (with gcc 11.1.0):
>>
>> from sound/oss/dmasound/dmasound_core.c:#1481, when falling from case 1
>> into case 0: (in arch/m68k/ selected builds only)
>>
>> 	case 1:
>> 		if ((size = ints[2]) < 256) /* check for small buffer specs */
>> 			size <<= 10 ;
>>                 if (size < MIN_BUFSIZE || size > MAX_BUFSIZE)
>>                         printk("dmasound_setup: invalid write buffer size, using default = %d\n", writeBufSize);
>>                 else
>>                         writeBufSize = size;
>> 	case 0:
>> 		break;
>> 	default:
>>
>> Can you tell me what is going on here?
> 
> As you can see the warning is suppressed when a case label falls through to
> a case that merely breaks... or returns, or continues (continue statement)
> or that goes to (goto statement) some other place.
> 
> However, Clang disagrees with this. See below for more:
> 
> https://github.com/ClangBuiltLinux/linux/issues/636
> https://godbolt.org/z/xgkvIh

I see. Thank you.

-- 
~Randy

Re: fallthrough question

[Joe Perches]

On Fri, 2022-02-18 at 13:57 -0800, Randy Dunlap wrote:
> Hi,
> 
> I expected this to produce a fallthrough warning, but it doesn't
> (with gcc 11.1.0):
> 
> from sound/oss/dmasound/dmasound_core.c:#1481, when falling from case 1
> into case 0: (in arch/m68k/ selected builds only)
> 
> 	case 1:
> 		if ((size = ints[2]) < 256) /* check for small buffer specs */
> 			size <<= 10 ;
>                 if (size < MIN_BUFSIZE || size > MAX_BUFSIZE)
>                         printk("dmasound_setup: invalid write buffer size, using default = %d\n", writeBufSize);
>                 else
>                         writeBufSize = size;
> 	case 0:
> 		break;
> 	default:
> 
> Can you tell me what is going on here?

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91432