compiler-rt/lib/trampoline_setup.c

//===----- trampoline_setup.c - Implement __trampoline_setup -------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include <stdint.h>
#include <stdlib.h>

extern void __clear_cache(void* start, void* end);

//
// The ppc compiler generates calls to __trampoline_setup() when creating 
// trampoline functions on the stack for use with nested functions.
// This function creates a custom 40-byte trampoline function on the stack 
// which loads r11 with a pointer to the outer function's locals
// and then jumps to the target nested function.
//
#if __ppc__
void __trampoline_setup(uint32_t* trampOnStack, int trampSizeAllocated, 
                                const void* realFunc, void* localsPtr)
{
    // should never happen, but if compiler did not allocate
    // enough space on stack for the trampoline, abort
    if ( trampSizeAllocated < 40 )
        abort();
    
    // create trampoline
    trampOnStack[0] = 0x7c0802a6;    // mflr r0
    trampOnStack[1] = 0x4800000d;    // bl Lbase
    trampOnStack[2] = (uint32_t)realFunc;
    trampOnStack[3] = (uint32_t)localsPtr;
    trampOnStack[4] = 0x7d6802a6;    // Lbase: mflr r11
    trampOnStack[5] = 0x818b0000;    // lwz    r12,0(r11)
    trampOnStack[6] = 0x7c0803a6;    // mtlr r0
    trampOnStack[7] = 0x7d8903a6;    // mtctr r12
    trampOnStack[8] = 0x816b0004;    // lwz    r11,4(r11)
    trampOnStack[9] = 0x4e800420;    // bctr
    
    // clear instruction cache
    __clear_cache(trampOnStack, &trampOnStack[10]);
}
#endif // __ppc__