Callling clib from assembly language

• Subject: Callling clib from assembly language
• From: "David N. Williams" <email@hidden>
• Date: Fri, 14 Apr 2006 15:53:29 -0400
• Delivered-to: email@hidden
• Delivered-to: email@hidden
• Organization: University of Michigan
• User-agent: Thunderbird 1.5 (Macintosh/20051201)

I'm porting the assembly language part of a Forth compiler
(kForth) to OS X ppc.  This is my first serious attempt at ppc
assembly language programming.  I've been using a "simplified"
linkage to clib functions, which is contrasted with the normal
linkage below.

My question is, what are the disadvantages of my approach?  I'm
wondering whether I'm going to regret not having done it the
normal way, somewhere down the line!

-- David W.

Here's the gcc 4.0.1 assembly language output for a C call to
sqrt():

----------------------
        ...
        bl L_sqrt$stub
        ...

        .section __TEXT,__picsymbolstub1,symbol_stubs,pure_instructions,32
        .align 5
L_sqrt$stub:
        .indirect_symbol _sqrt
        mflr r0
        bcl 20,31,"L00000000001$spb"
"L00000000001$spb":
        mflr r11
        addis r11,r11,ha16(L_sqrt$lazy_ptr-"L00000000001$spb")
        mtlr r0
        lwzu r12,lo16(L_sqrt$lazy_ptr-"L00000000001$spb")(r11)
        mtctr r12
        bctr
        .lazy_symbol_pointer
L_sqrt$lazy_ptr:
        .indirect_symbol _sqrt
        .long   dyld_stub_binding_helper
----------------------

Here's what I'm using:

---------------------
                .data
kf_sqrt:        .long _sqrt

                .text
        ...
        addis   r2,0,ha16(kf_sqrt)
        lwz     r0,lo16(kf_sqrt)(r2)
        mtctr   r0
        bctrl
        ...
---------------------

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