csg@pyramid.pyramid.com (Carl S. Gutekunst) (01/06/88)
In a recent battle to port gcc to a Pyramid 98x, I cobbled up my own version of the alloca(3) function. Since it doesn't work very well, I decided to post it to the net. :-) See the caveats in the comments; it is not possible to make alloca() work like it does on a VAX or a 680x0, but this works pretty well in large programs that declare lots of automatic arrays and structs. The difference between my version and the one provided with GNU Emacs is that mine tries to prevent objects from straddling the Pyramid's cache boundaries; this is a big win when allocating large numbers of small blocks (8 to 32 bytes). DISCLAIMER: I am posting this as a Pyramid user, and NOT as a representative of Pyramid Technology Corp. This code *will* fail in many applications that work just fine on a VAX or 680x0, and is intended only as a stopgap measure to get code running until it can be modified to not use alloca(), or someone defines a way for C to dynamically declare automatic arrays. (Hope! :-)) Problems -> csg@pyramid.com, NOT to pyramid!bugs. <csg> _______________________________________________________________________________ .text 1 _RCSid: .ascii "@(#) alloca.s $Revision: 1.1 $ $Date: 88/01/04 13:53:05 $" # # alloca.s -- a crude implementation of alloca() for the Pyramid 90x # # This function performs the basic function of the VAX alloca(3) call: # allocate a requested block of memory on the data stack, and return # the starting address to the caller. The assumption is that the space # requested will be released upon function exit. # # The Pyramid CLE code generator does not normally save and restore the # data stack frame on C functions (that is, a plain "ret" is done instead # of an "adsf" and "retd"), so this space might *not* go away on exit. # Fortunately, a "retd" instruction executed by a parent of the calling # function will release the space, and the code generator always produces # addresses relative to CFP, not SP. Hence the worst consequence of this # function is stack overflow. # # In general, this function can be used successfully if: # # - The calling function or its parent declares local structures or # arrays, which forces generation of "adsf" and "retd"; # # - The calling function is not called recursively or inside a loop; # # - The calling function is not running inside a signal handler. # # NOTE: To improve performance, this function attempts to keep objects # from straddling 32-byte cache boundaries. This means that there may be # "holes" between consecutively allocated objects. # # NOTE: This function may leave the SP on a non-32-byte boundary. The # CLE code generator, for optimization purposes, assumes that the SP is # always kept 32-byte aligned. This may affect performance of functions # called by the parent function of alloca(). .text 0 .globl _alloca _alloca: addw $3,pr0 # Round the request to an int boundary andw $-4,pr0 # / cmpw $32,pr0 # Is the request >= 32? bge alloca_big # Yes, return SP 32-byte aligned movw sp,lr0 # Truncate SP to cache boundary andw $-32,lr0 # / movw sp,lr1 # Calculate distance to boundary subw lr0,lr1 # / subw pr0,sp # Subtract the request from the SP cmpw lr0,sp # Cross a boundary? bge alloca_ret # Nope, so we're done. subw lr1,sp # Yes, move down the minimum distance alloca_ret: movw sp,pr0 # Return the new SP ret alloca_big: subw pr0,sp # Allocate requested space on Stack andw $-32,sp # Truncate to 32-byte boundary movw sp,pr0 # Return the new SP ret
karl@triceratops.cis.ohio-state.edu (Karl Kleinpaste) (03/21/89)
pete@sun360.Online.Nixdorf.De (pete delany) writes:
Could someone send a copy of alloca() for OSX 4.1;
You've already got it:
[78] [8:09am] tut:/n/dinosaur/0/karl> nm /usr/.attlib/libPW.a | grep alloca
U _alloca
U _alloca
alloca.o:
00000000 T _alloca
--Karlzap@nada.kth.se (Svante Lindahl) (03/22/89)
In article <KARL.89Mar21080920@triceratops.cis.ohio-state.edu> karl@triceratops.cis.ohio-state.edu (Karl Kleinpaste) writes: >pete@sun360.Online.Nixdorf.De (pete delany) writes: > Could someone send a copy of alloca() for OSX 4.1; > >You've already got it: >[78] [8:09am] tut:/n/dinosaur/0/karl> nm /usr/.attlib/libPW.a | grep alloca That version differs slightly from the one that is distributed with Gnu Emacs (in file src/alloca.s). From that file: .globl _alloca _alloca: addw $3,pr0 # add 3 (dec) to first argument bicw $3,pr0 # then clear its last 2 bits subw pr0,sp # subtract from SP the val in PR0 andw $-32,sp # keep sp aligned on multiple of 32. movw sp,pr0 # ret. current SP ret Svante