Re: [musl] [PATCH 1/1] IN6_IS_ADDR_LOOPBACK() and similar macros warn on -Wcast-qual

[Brad House <brad@brad-house.com>]

Any update on maybe merging the updated patch from this chain?

Thanks.

-Brad

On 8/14/24 5:24 PM, enh wrote:
> not quite the question you asked, but the new implementation is what
> bionic has shipped since 2016, and had the historical castful
> implementation before that. (citation needed?
> https://android-review.googlesource.com/c/platform/bionic/+/250098)
>
> On Wed, Aug 14, 2024 at 5:16 PM Rich Felker <dalias@libc.org> wrote:
>> On Fri, Aug 02, 2024 at 08:02:16PM -0400, Brad House wrote:
>>> On 8/2/24 7:38 PM, Rich Felker wrote:
>>>
>>>> On Fri, Aug 02, 2024 at 05:27:26PM -0400, Brad House wrote:
>>>>> I'm the maintainer of c-ares (https://c-ares.org) and have been
>>>>> scanning the CI build logs for various systems to catch warnings,
>>>>> and on Alpine Linux (which obviously uses musl c) we get these
>>>>> warnings, specifically when using clang (but not oddly not on gcc):
>>>>>
>>>>> /__w/c-ares/c-ares/src/lib/ares__sortaddrinfo.c:93:9: warning: cast
>>>> >from 'const struct in6_addr *' to 'unsigned char *' drops const
>>>>> qualifier [-Wcast-qual]
>>>>>     93 |     if (IN6_IS_ADDR_MULTICAST(&addr6->sin6_addr)) {
>>>>>        |         ^
>>>>> /usr/include/netinet/in.h:120:48: note: expanded from macro
>>>>> 'IN6_IS_ADDR_MULTICAST'
>>>>>    120 | #define IN6_IS_ADDR_MULTICAST(a) (((uint8_t *) (a))[0] == 0xff)
>>>>>        |                                                ^
>>>>> ...       ^
>>>>>
>>>>> Full build output: https://github.com/c-ares/c-ares/actions/runs/10219723015/job/28278549865
>>>>>
>>>>> I've attached a patch that will silence this warning by always
>>>>> casting to the comparison to const, but otherwise not impact the
>>>>> behavior.
>>>>>
>>>>> -Brad
>>>>> diff --git a/include/netinet/in.h b/include/netinet/in.h
>>>>> index fb628b61..f04657f3 100644
>>>>> --- a/include/netinet/in.h
>>>>> +++ b/include/netinet/in.h
>>>>> @@ -108,46 +108,63 @@ uint16_t ntohs(uint16_t);
>>>>>   #define IPPROTO_MAX      263
>>>>> ...
>>>>>   #define IN6_IS_ADDR_LOOPBACK(a) \
>>>>> -        (((uint32_t *) (a))[0] == 0 && ((uint32_t *) (a))[1] == 0 && \
>>>>> -         ((uint32_t *) (a))[2] == 0 && \
>>>>> -         ((uint8_t *) (a))[12] == 0 && ((uint8_t *) (a))[13] == 0 && \
>>>>> -         ((uint8_t *) (a))[14] == 0 && ((uint8_t *) (a))[15] == 1 )
>>>>> +        (((const uint32_t *) (a))[0] == 0 && \
>>>>> +         ((const uint32_t *) (a))[1] == 0 && \
>>>>> +         ((const uint32_t *) (a))[2] == 0 && \
>>>>> +         ((const uint8_t *) (a))[12] == 0 && \
>>>>> +         ((const uint8_t *) (a))[13] == 0 && \
>>>>> +         ((const uint8_t *) (a))[14] == 0 && \
>>>>> +         ((const uint8_t *) (a))[15] == 1 )
>>>>> ...
>>>> It looks like there's a lot wrong with these macros. They should not
>>>> be doing random pointer casts like they are. Per the standard, they
>>>> take an argument of type const struct in6_addr *, so they should
>>>> almost surely be operating on that type directly. That would make them
>>>> actually type-safe (diagnostic if called with wrong argument type).
>>>>
>>>> I guess we should look at whether there's any good reason they were
>>>> written the way they were..
>>>>
>>>> Rich
>>> Yep, I see what you mean.  There are already accessors for 8, 16,
>>> and 32bit into struct in6_addr so its odd not to use those.  I've
>>> attached a v2 patch that uses those instead which also cleans up the
>>> warnings.
>>>
>>> -Brad
>>> diff --git a/include/netinet/in.h b/include/netinet/in.h
>>> index fb628b61..c6afeed8 100644
>>> --- a/include/netinet/in.h
>>> +++ b/include/netinet/in.h
>>> @@ -108,51 +108,68 @@ uint16_t ntohs(uint16_t);
>>>   #define IPPROTO_MAX      263
>>>
>>>   #define IN6_IS_ADDR_UNSPECIFIED(a) \
>>> -        (((uint32_t *) (a))[0] == 0 && ((uint32_t *) (a))[1] == 0 && \
>>> -         ((uint32_t *) (a))[2] == 0 && ((uint32_t *) (a))[3] == 0)
>>> +        (((a)->s6_addr32)[0] == 0 && \
>>> +         ((a)->s6_addr32)[1] == 0 && \
>>> +         ((a)->s6_addr32)[2] == 0 && \
>>> +         ((a)->s6_addr32)[3] == 0)
>>>
>>>   #define IN6_IS_ADDR_LOOPBACK(a) \
>>> -        (((uint32_t *) (a))[0] == 0 && ((uint32_t *) (a))[1] == 0 && \
>>> -         ((uint32_t *) (a))[2] == 0 && \
>>> -         ((uint8_t *) (a))[12] == 0 && ((uint8_t *) (a))[13] == 0 && \
>>> -         ((uint8_t *) (a))[14] == 0 && ((uint8_t *) (a))[15] == 1 )
>>> +        (((a)->s6_addr32)[0] == 0 && \
>>> +         ((a)->s6_addr32)[1] == 0 && \
>>> +         ((a)->s6_addr32)[2] == 0 && \
>>> +         ((a)->s6_addr)[12] == 0 && \
>>> +         ((a)->s6_addr)[13] == 0 && \
>>> +         ((a)->s6_addr)[14] == 0 && \
>>> +         ((a)->s6_addr)[15] == 1 )
>>>
>>> -#define IN6_IS_ADDR_MULTICAST(a) (((uint8_t *) (a))[0] == 0xff)
>>> +#define IN6_IS_ADDR_MULTICAST(a) (((a)->s6_addr)[0] == 0xff)
>>>
>>>   #define IN6_IS_ADDR_LINKLOCAL(a) \
>>> -        ((((uint8_t *) (a))[0]) == 0xfe && (((uint8_t *) (a))[1] & 0xc0) == 0x80)
>>> +        ((((a)->s6_addr)[0]) == 0xfe && \
>>> +         (((a)->s6_addr)[1] & 0xc0) == 0x80)
>>>
>>>   #define IN6_IS_ADDR_SITELOCAL(a) \
>>> -        ((((uint8_t *) (a))[0]) == 0xfe && (((uint8_t *) (a))[1] & 0xc0) == 0xc0)
>>> +        ((((a)->s6_addr)[0]) == 0xfe && \
>>> +         (((a)->s6_addr)[1] & 0xc0) == 0xc0)
>>>
>>>   #define IN6_IS_ADDR_V4MAPPED(a) \
>>> -        (((uint32_t *) (a))[0] == 0 && ((uint32_t *) (a))[1] == 0 && \
>>> -         ((uint8_t *) (a))[8] == 0 && ((uint8_t *) (a))[9] == 0 && \
>>> -         ((uint8_t *) (a))[10] == 0xff && ((uint8_t *) (a))[11] == 0xff)
>>> +        (((a)->s6_addr32)[0] == 0 && \
>>> +         ((a)->s6_addr32)[1] == 0 && \
>>> +         ((a)->s6_addr)[8] == 0 && \
>>> +         ((a)->s6_addr)[9] == 0 && \
>>> +         ((a)->s6_addr)[10] == 0xff && \
>>> +         ((a)->s6_addr)[11] == 0xff)
>>>
>>>   #define IN6_IS_ADDR_V4COMPAT(a) \
>>> -        (((uint32_t *) (a))[0] == 0 && ((uint32_t *) (a))[1] == 0 && \
>>> -         ((uint32_t *) (a))[2] == 0 && ((uint8_t *) (a))[15] > 1)
>>> +        (((a)->s6_addr32)[0] == 0 && \
>>> +         ((a)->s6_addr32)[1] == 0 && \
>>> +         ((a)->s6_addr32)[2] == 0 && \
>>> +         ((a)->s6_addr)[15] > 1)
>>>
>>>   #define IN6_IS_ADDR_MC_NODELOCAL(a) \
>>> -        (IN6_IS_ADDR_MULTICAST(a) && ((((uint8_t *) (a))[1] & 0xf) == 0x1))
>>> +        (IN6_IS_ADDR_MULTICAST(a) && \
>>> +         ((((a)->s6_addr)[1] & 0xf) == 0x1))
>>>
>>>   #define IN6_IS_ADDR_MC_LINKLOCAL(a) \
>>> -        (IN6_IS_ADDR_MULTICAST(a) && ((((uint8_t *) (a))[1] & 0xf) == 0x2))
>>> +        (IN6_IS_ADDR_MULTICAST(a) && \
>>> +         ((((a)->s6_addr)[1] & 0xf) == 0x2))
>>>
>>>   #define IN6_IS_ADDR_MC_SITELOCAL(a) \
>>> -        (IN6_IS_ADDR_MULTICAST(a) && ((((uint8_t *) (a))[1] & 0xf) == 0x5))
>>> +        (IN6_IS_ADDR_MULTICAST(a) && \
>>> +         ((((a)->s6_addr)[1] & 0xf) == 0x5))
>>>
>>>   #define IN6_IS_ADDR_MC_ORGLOCAL(a) \
>>> -        (IN6_IS_ADDR_MULTICAST(a) && ((((uint8_t *) (a))[1] & 0xf) == 0x8))
>>> +        (IN6_IS_ADDR_MULTICAST(a) && \
>>> +         ((((a)->s6_addr)[1] & 0xf) == 0x8))
>>>
>>>   #define IN6_IS_ADDR_MC_GLOBAL(a) \
>>> -        (IN6_IS_ADDR_MULTICAST(a) && ((((uint8_t *) (a))[1] & 0xf) == 0xe))
>>> +        (IN6_IS_ADDR_MULTICAST(a) && \
>>> +         ((((a)->s6_addr)[1] & 0xf) == 0xe))
>>>
>>>   #define __ARE_4_EQUAL(a,b) \
>>>        (!( (0[a]-0[b]) | (1[a]-1[b]) | (2[a]-2[b]) | (3[a]-3[b]) ))
>>>   #define IN6_ARE_ADDR_EQUAL(a,b) \
>>> -     __ARE_4_EQUAL((const uint32_t *)(a), (const uint32_t *)(b))
>>> +     __ARE_4_EQUAL((a)->s6_addr32, (b)->s6_addr32)
>>>
>>>   #define      IN_CLASSA(a)            ((((in_addr_t)(a)) & 0x80000000) == 0)
>>>   #define      IN_CLASSA_NET           0xff000000
>> I think this looks fine. Anyone willing to point a second set of eyes
>> at it (or maybe write a test to check whether codegen is same before
>> and after) and make sure before I merge it?
>>
>> Rich