Re: [PATCH v11 18/19] module: fix types of device tables aliases

From: Andrey Ryabinin
Date: Mon Feb 16 2015 - 09:01:33 EST

On 02/16/2015 05:44 AM, Rusty Russell wrote:
> Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx> writes:
>> MODULE_DEVICE_TABLE() macro used to create aliases to device tables.
>> Normally alias should have the same type as aliased symbol.
>> Device tables are arrays, so they have 'struct type##_device_id[x]'
>> types. Alias created by MODULE_DEVICE_TABLE() will have non-array type -
>> 'struct type##_device_id'.
>> This inconsistency confuses compiler, it could make a wrong
>> assumption about variable's size which leads KASan to
>> produce a false positive report about out of bounds access.
> Hmm, as Andrew Morton points out, this breaks some usage; if we just
> fix the type (struct type##_device_id[]) will that work instead?
> I'm guessing not, since typeof(x) will presumably preserve sizing
> information?

Yes, this won't work.
In this particular case 'struct type##_device_id[]' would be equivalent
to 'struct type##_device_id[1]'

$ cat test.c
struct d {
int a;
int b;
struct d arr[] = {
{1, 2}, {3, 4}, {}
extern struct d arr_alias[] __attribute__((alias("arr")));

$ gcc -c test.c
test.c:8:17: warning: array âarr_aliasâ assumed to have one element
extern struct d arr_alias[] __attribute__((alias("arr")));

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