Re: [RFC] Use custom hash function with bcache

[sami wagiaalla <swagiaal at redhat dot com>]

> This patch means that a given bcache could include two objects of the
> same size that have different hash and comparison functions.  So, it
> seems like some kind of clash could (in theory) result.  This is very
> bad if one object is mutable and the other is not.
>
> I think it would be safer to either:

I will take door number 1 since I am already working on it :)

> 1. Make the hash and comparison functions part of the bcache itself, set
>     only when the bcache is allocated,

This is what Doug suggested. Making the functions part of the bcache 
struct and assigning them when bcache_xmalloc is called.

 then audit all uses of this
>     particular bcache to make sure that only psymtabs are added to it
>     (this could be done by introducing a new type, so that invalid uses
>     are compile-time errors),

with the above change the bcaches will be initialized like this:

objfile->psymbol_cache = bcache_xmalloc (psymbol_hash, psymbol_compare);
objfile->macro_cache = bcache_xmalloc (NULL, NULL);
objfile->filename_cache = bcache_xmalloc (NULL, NULL);

So only objects added to the psymbol_cache would be subjected to the new 
hash and compare functions. Although, you are right, there is no strict 
type checking. Are you suggesting we make psymbol_cache a new type ?

> I think you can make the psym hash and comparison functions a bit
> simpler by just skipping the pointer-sized lang-specific hole.  This is
> maybe more future-proof as well.

This patch already does that :)