On Mon, 21 Jan 2002, Kevin D. Kissell wrote: > If anything, assuming that k0 or k1 are sane in > compiler-generated code is more of a violation > of the ABI than imposing an optional use of s7. > Sony's use in libraries is somewhat less intrusive. Hmm, it's a glibc/kernel internal implementation detail. I don't think this is an ABI violation, as from a program's point of view k0/k1 are still "undefined -- do not use". > It's a common technique to bind a static register > to a global variable. Linking to libraries with no > knowledge of this variable breaks nothing, since > by the ABI, all use of "s" registers requires that > they be preserved and returned intact to the caller. > It seems to me to be quite straightforward to apply > this technique to the thread register. The *only* > issue I see is that of performance, and it is by > no means clear how severe this would be. The k0/k1 approach is a performance hit as well. Possibly a worse one, as you lose a few cycles unconditionally every exception, while having one static register less in the code can be dealt with by a compiler in a more flexible way. > In the compiled code that I have examined > for compiler efficiency in the past, it's pretty > rare that *all* static registers are actually used. Even with one register less there are still eight remaining, indeed. -- + Maciej W. Rozycki, Technical University of Gdansk, Poland + +--------------------------------------------------------------+ + e-mail: macro@ds2.pg.gda.pl, PGP key available +
