Re: gperf 3.1 changes the type of the hash 'len' parameter

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On Fri, Jan 27, 2017 at 09:09:14AM +0000, Richard W.M. Jones wrote:
> I pushed gperf 3.1 to Rawhide.
> 
> This changes the type of one of the parameters of the generated
> perfect hash function:
> 
> -char *in_word_set (register const char *str, register unsigned int len);
> +char *in_word_set (register const char *str, register size_t len);
> 
> If you have the function prototyped in another file, then you have to
> be careful that the prototype exactly matches the new type.  Otherwise
> on 64 bit architectures you'll end up passing an incorrectly sized
> 'len' argument (unsigned int == 32 bits vs size_t == 64 bits) which
> will subtly break in certain circumstances (but on little endian it'll
> still work most of the time, making this bug rather insidious).
> 
> Using the functions (third) section of the gperf file can avoid
> needing to prototype the function elsewhere, since you can drop a
> wrapper of your own choosing into the functions section.

There was a bit of fallout from this change.  Mainly it broke
systemd, although there was already a fix upstream.

If you're wondering how to fix this, here are two approaches you can
take.

Firstly the systemd fix which involves sensing the function signature
at ./configure time and adjusting the prototype:

https://github.com/systemd/systemd/commit/c9f7b4d356a453a01aa77a6bb74ca7ef49732c08

Alternately, this is the approach I took for libguestfs.  Move all
calls to the hash function into the functions (third) section of the
gperf source file, so no explicit prototype is needed:

https://github.com/libguestfs/libguestfs/commit/004de6cf45cfe66ca166cbdcb1c3125a2a81eb31
https://github.com/libguestfs/libguestfs/commit/48d4117789e92489b9a3c6f3456b0770b3fdb290

Hope that helps others who have gperf problems.  You can also follow
up here if you don't know how to fix it for a particular package and
I'll see if I can help.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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