Re: [Qemu-devel] [PATCH v2 3/4] trace: forbid use of %m in trace event format strings

[Thomas Huth]

On 22/01/2019 19.10, Eric Blake wrote:
> On 1/22/19 11:23 AM, Daniel P. Berrangé wrote:
> 
>>
>>>> On this point though, does anyone know of any platforms we support[1],
>>>> or are likely to support in future, where 'strerror' is *not* thread
>>>> safe ?
>>>
>>> I'm not coming up with one, and I think the problem is independent of
>>> this series (if we DO have a problem, it's a series all its own to
>>> eradicate the use of strerror() in favor of something safer, either
>>> picking strerror_l() or dealing with the glibc vs. BSD differences in
>>> strerror_r()).
>>
>> Agree that its not really something for this series - this just
>> made me think of it again.
> 
> Shoot - FreeBSD strerror() is not threadsafe:
> https://github.com/freebsd/freebsd/blob/master/lib/libc/string/strerror.c#L119
> 
> char *
> strerror(int num)
> {
>       static char ebuf[NL_TEXTMAX];
> 
>       if (strerror_r(num, ebuf, sizeof(ebuf)) != 0)
>               errno = EINVAL;
>       return (ebuf);
> }
> 
>>
>> We went through the scrubbing in libvirt to use the sane, but still
>> tedious to call, variant of strerror_r() many years ago. With luck
>> though it is a worry that can be confined the dustbin of ancient
>> UNIX history....unless someone can point to evidence to the contrary ?
> 
> libvirt has it easy - they let gnulib do all the work of futzing around
> with getting a working strerror() despite platform bugs and despite
> glibc's insistence on a non-POSIX signature if _GNU_SOURCE is defined.
> We'll have to do a bit more legwork.
> 
> That said, I've added it to:
> https://wiki.qemu.org/Contribute/BiteSizedTasks#Error_checking
> 
> if someone wants to do the grunt work.

I think we should change that task to switch to g_strerror() from glib
instead ... as far as I can see, this is a proper wrapper around
strerror_r(), so we don't have to deal with the implementation oddities
of strerror_r() in QEMU.

 Thomas

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