Re: linux uml segfault

[Johannes Berg <johannes@sipsolutions.net>]

On 5 March 2021 18:39:42 CET, Anton Ivanov <anton.ivanov@kot-begemot.co.uk> wrote:
>
>
>On 04/03/2021 07:47, Johannes Berg wrote:
>> On Thu, 2021-03-04 at 14:38 +0900, Hajime Tazaki wrote:
>> 
>>>> Now, I don't know how to fix it (short of changing your nsswitch
>>>> configuration) - maybe we could somehow rename sem_init()? Or maybe
>we
>>>> can somehow give the kernel binary a lower symbol resolution than
>the
>>>> libc/libpthread.
>>>
>>> objcopy (from binutils) can localize symbols (i.e., objcopy -L
>>> sem_init $orig_file $new_file).  It also does renaming symbols.  But
>>> not sure this is the ideal solution.
>> 
>> Yes, we started thinking about it but it was too late at night when I
>> replied ...
>> 
>> I think there's basically a way to have an external list of symbols
>to
>> export, for symbol versioning, that we could/should use to basically
>not
>> export any of the kernel symbols out to libs.
>> 
>>> How does UML handle symbol conflicts between userspace code and
>Linux
>>> kernel (like this case sem_init) ?  AFAIK, libnl has a same symbol
>as
>>> Linux kernel (genlmsg_put) and others can possibly do as well.
>> 
>> I fear it doesn't?
>
>Let's assume it does not, and try to fix this by de-conflicting the
>symbol.
>For the time being, also, let's aim for a Debian specific patch just to
>go into their "patches" dir for build so that UML is not dropped out of
>the release.
>
>This should make all internal uses of sem_init be um_sem_init in the
>actual object files. I will chase the issue of it picking up glibc
>memcpy separately.
>Upon close inspection it looks like a different issue - it is in the
>other direction (picking a dynamic symbol instead of the one from the
>tree). I spent all day chasing it today and I cannot reproduce it. At
>the same time it was reproducible yesterday without any problems :(

>+#ifdef CONFIG_UML
>+void __init um_sem_init(void)
>+#else
>  void __init sem_init(void)
>+#endif

Might be easier to just

#define sem_init um_sem_init

in an appropriate header file, perhaps even in arch/um/? 


johannes
-- 
Sent from my phone. 

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