Re: [RFC] Avoiding _divsi3 call during ld.so bootstrap

[Bob Wilson <bwilson at tensilica dot com>]

John Reiser wrote:
> Implement a subroutine _divsi3 which checks the divisor for being 12
> (which is sizeof(RELA)), then takes advantage of 1/12 = 0.010101... in binary
> to perform the division by 12 using the strategy of umulsi3_highpart
> (multiply by a binary fraction, take the high part) as Richard suggests.

Ah but you missed the point -- the existing _divsi3 function works just fine. 
The problem is that function calls don't work until ld.so is relocated. 
Whatever code GCC generates for this division would have to be done entirely 
in-line.  Obviously that's not desirable for general-purpose code, so it would 
mean adding a special option to GCC that would only be used in this one place. 
Yuck.

An alternative is yet another special GCC option to generate a PC-relative call 
that does not require any relocation (assuming we can arrange for the _divsi3 
routine to be located within the limited range of Xtensa's PC-relative call 
instruction).  That seems somewhat better, but it would still be a 
special-purpose option with no other intended use (at least for now).

Thanks for your suggestion, though.  I'm not going to decide on any course of 
action right now.

--Bob