From: Linus Torvalds <torvalds@linux-foundation.org>
To: Ingo Molnar <mingo@kernel.org>,
Igor Lubashev <ilubashe@akamai.com>,
Josh Hunt <johunt@akamai.com>, Vishwanath Pai <vpai@akamai.com>,
Pablo Neira Ayuso <pablo@netfilter.org>
Cc: Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>,
"the arch/x86 maintainers" <x86@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Brian Gerst <brgerst@gmail.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Juergen Gross <jgross@suse.com>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Kees Cook <keescook@chromium.org>,
Andrew Morton <akpm@linux-foundation.org>,
"David S. Miller" <davem@davemloft.net>
Subject: xt_hashlimig build error (was Re: [RFC 01/17] x86/asm/64: Remove the restore_c_regs_and_iret label)
Date: Thu, 7 Sep 2017 10:51:21 -0700 [thread overview]
Message-ID: <CA+55aFznorYJd8OyV09eHt4zrRrrv2aEq_D=Q8k2w+CmgJ=+cw@mail.gmail.com> (raw)
On Thu, Sep 7, 2017 at 3:29 AM, Ingo Molnar <mingo@kernel.org> 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
next reply other threads:[~2017-09-07 17:51 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-07 17:51 Linus Torvalds [this message]
2017-09-07 18:25 ` xt_hashlimig build error (was Re: [RFC 01/17] x86/asm/64: Remove the restore_c_regs_and_iret label) Vishwanath Pai
2017-09-07 18:43 ` Linus Torvalds
2017-09-07 20:16 ` Vishwanath Pai
2017-09-07 20:41 ` Lubashev, Igor
2017-09-07 20:45 ` Linus Torvalds
2017-09-07 21:21 ` Vishwanath Pai
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