Re: [PATCH v1] uml: remove support for CONFIG_STATIC_LINK

From: Anton Ivanov <anton.ivanov@cambridgegreys.com>
To: Richard Weinberger <richard@nod.at>,
	Brendan Higgins <brendanhiggins@google.com>
Cc: Johannes Berg <johannes.berg@intel.com>,
	Jeff Dike <jdike@addtoit.com>,
	linux-um <linux-um@lists.infradead.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	davidgow@google.com
Subject: Re: [PATCH v1] uml: remove support for CONFIG_STATIC_LINK
Date: Tue, 10 Dec 2019 07:34:35 +0000	[thread overview]
Message-ID: <346757c8-c111-f6cf-21d2-b0bffd41b8a8@cambridgegreys.com> (raw)
In-Reply-To: <2eecf4dc-eb96-859a-a015-1a4f388b57a2@cambridgegreys.com>

On 10/12/2019 07:20, Anton Ivanov wrote:
> On 09/12/2019 23:15, Richard Weinberger wrote:
>> ----- Ursprüngliche Mail -----
>>> Von: "Brendan Higgins" <brendanhiggins@google.com>
>>> An: "Jeff Dike" <jdike@addtoit.com>, "richard" <richard@nod.at>, 
>>> "anton ivanov" <anton.ivanov@cambridgegreys.com>
>>> CC: "Johannes Berg" <johannes.berg@intel.com>, "linux-um" 
>>> <linux-um@lists.infradead.org>, "linux-kernel"
>>> <linux-kernel@vger.kernel.org>, davidgow@google.com, "Brendan 
>>> Higgins" <brendanhiggins@google.com>
>>> Gesendet: Dienstag, 10. Dezember 2019 00:02:48
>>> Betreff: [PATCH v1] uml: remove support for CONFIG_STATIC_LINK
>>
>>> CONFIG_STATIC_LINK appears to have been broken since before v4.20. It
>>> doesn't play nice with CONFIG_UML_NET_VECTOR=y:
>>>
>>> /usr/bin/ld: arch/um/drivers/vector_user.o: in function
>>> `user_init_socket_fds': vector_user.c:(.text+0x430): warning: Using
>>> 'getaddrinfo' in statically linked applications requires at runtime the
>>> shared libraries from the glibc version used for linking
>>
>> This is nothing serious.
>>
>>> And it seems to break the ptrace check:
>>>
>>> Checking that ptrace can change system call numbers...check_ptrace :
>>> child exited with exitcode 6, while expecting 0; status 0x67f
>>> [1]    126822 abort      ./linux mem=256M
>>
>> Didn't we fix that already?
> 
> Yes we did - I commented on this.
> 
>>
>>> (Apparently, a patch was recently discussed that fixes this - around
>>> v5.5-rc1[1] - but the fact that this was broken for over a year
>>> remains.)
>>>
>>> According to Anton, PCAP throws even more warnings, and the resulting
>>> binary isn't really even static anyway, so there is really no point in
>>> keeping this config around[2].
>>
>> What?
>> Anton, please explain. Why is it not static when build with 
>> CONFIG_STATIC_LINK?
> 
> 
> LIBC itself tries to dynamic load stuff internally.
> 
> It is beyond our control and it claims that it will work only on EXACTLY 
> the same version of libc library as the one used for static link.
> 
> So you get a not-exactly static binary which is not properly moveable 
> between systems.
> 
> This is specifically in the name resolution, etc parts of libc which all 
> of: pcap, vector, vde, etc rely on.
> 
> Another alternative is to turn off static specifically for those.
> 
> Further to this - any properly written piece of networking code which 
> uses the newer functions for name/service resolution will have the same 
> problem. You can be static only if you do everything "manually" the old 
> way.

The offending piece of code is the glibc implementation of getaddrinfo().

If you use it and link static the resulting binary is not really static.

> 
>>
>> Thanks,
>> //richard
>>
>> _______________________________________________
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>> http://lists.infradead.org/mailman/listinfo/linux-um
>>
> 
> 

-- 
Anton R. Ivanov
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https://www.cambridgegreys.com/