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

[Eric Blake]

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.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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