gas/hash.c: add interface for looking up non-NUL-terminated strings
Zack Weinberg
zack@codesourcery.com
Mon Apr 4 05:33:00 GMT 2005
Alan Modra <amodra@bigpond.net.au> writes:
> On Tue, Mar 29, 2005 at 12:00:37PM -0800, Zack Weinberg wrote:
>>
>> The appended patch adds a new interface to gas/hash.c, hash_find_n,
>> with exactly the same semantics as hash_find except that the length of
>> the key is passed in as an argument, and the key is not assumed to be
>> NUL-terminated. This is more convenient when parsing an assembly
>> instruction: one does not need to write a NUL into the line buffer so
>> that hash_find knows where to stop.
>
> Hmm, seems to me that writing a NUL into the line buffer isn't that
> onerous.
I suppose to some extent it's a matter of taste, but having this
interface available allows me to make dramatic simplifications in
tc-arm.c. I should have something to show y'all sometime this week on
that score.
> I'd like to see more justification for this patch, particularly
> since we have too many hash table implementations already in
> binutils. At some stage I'd like to move bfd and gas over to use
> libiberty's hashtab.c, and another interface difference will make
> that task harder.
For what GAS uses hash tables for, I don't think that's a good idea.
libiberty's hashtab.c is extremely generic; you'd have to write
nontrivial amounts of wrapper code, and you'd take a nasty performance
hit. (multiple indirect function calls on every lookup).
cpplib's symtab.c might be a better fit (it can be used independently
from the rest of cpplib) -- and it already has this interface. :)
>> - if (strcmp (p->string, key) == 0)
>> + if (p->string[len] == '\0' && strncmp (p->string, key, len) == 0)
>
> Potential access past the end of p->string. The strncmp must come
> first.
Good point, will correct in my copy.
zw
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