github.com/mh-cbon/go@v0.0.0-20160603070303-9e112a3fe4c0/src/runtime/sys_s390x.go (about)

     1  // Copyright 2016 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package runtime
     6  
     7  import "unsafe"
     8  
     9  // adjust Gobuf as if it executed a call to fn with context ctxt
    10  // and then did an immediate Gosave.
    11  func gostartcall(buf *gobuf, fn, ctxt unsafe.Pointer) {
    12  	if buf.lr != 0 {
    13  		throw("invalid use of gostartcall")
    14  	}
    15  	buf.lr = buf.pc
    16  	buf.pc = uintptr(fn)
    17  	buf.ctxt = ctxt
    18  }
    19  
    20  // Called to rewind context saved during morestack back to beginning of function.
    21  // To help us, the linker emits a jmp back to the beginning right after the
    22  // call to morestack. We just have to decode and apply that jump.
    23  func rewindmorestack(buf *gobuf) {
    24  	var inst uint64
    25  	if buf.pc&1 == 0 && buf.pc != 0 {
    26  		inst = *(*uint64)(unsafe.Pointer(buf.pc))
    27  		switch inst >> 48 {
    28  		case 0xa7f4: // BRC (branch relative on condition) instruction.
    29  			inst >>= 32
    30  			inst &= 0xFFFF
    31  			offset := int64(int16(inst))
    32  			offset <<= 1
    33  			buf.pc += uintptr(offset)
    34  			return
    35  		case 0xc0f4: // BRCL (branch relative on condition long) instruction.
    36  			inst >>= 16
    37  			inst = inst & 0xFFFFFFFF
    38  			inst = (inst << 1) & 0xFFFFFFFF
    39  			buf.pc += uintptr(int32(inst))
    40  			return
    41  		}
    42  	}
    43  	print("runtime: pc=", hex(buf.pc), " ", hex(inst), "\n")
    44  	throw("runtime: misuse of rewindmorestack")
    45  }