On Thu, Sep 7, 2017 at 3:29 AM, Ingo Molnar <[email protected]> wrote:
>
> not the best of kernels, 32-bit allyesconfig doesn't even appear to build:
>
> net/netfilter/xt_hashlimit.o: In function `hashlimit_mt_common.isra.6':
> xt_hashlimit.c:(.text+0x1146): undefined reference to `__udivdi3'
I think this is due to commit bea74641e378 ("netfilter: xt_hashlimit:
add rate match mode").
It adds a 64-bit divide in user2rate_bytes() afaik, and to make things
worse it seems to be a really stupid one too.
Although I guess "worse" is not bad when the stupidity of it should
mean that it's easy to avoid the 64-bit issue.
Oddly, user2rate() that actually *does* need a 64-bit divide, seems to
do it right and use "div64_u64()" to do so.
But user2rate_bytes() could easily avoid any 64-bit issues, since it
divides the max 32-bit (unsigned) number with a 64-bit unsigned
number.
It would be easy to just say
- "if high 32 bits are set, result is 0"
- else do a 32-bit divide
or just use "div64_u64()" in that code too.
But honestly, that math is odd in other ways too (is that "r-1"
_supposed_ to underflow to -1 for large 'user' counts?), so somebody
needs to look at that logic.
And there might be some other 64-bit divide I missed, so please,
netfilter people, check the 32-bit build.
Linus
