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// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package runtime
import "unsafe"
// adjust Gobuf as if it executed a call to fn with context ctxt
// and then did an immediate Gosave.
func gostartcall(buf *gobuf, fn, ctxt unsafe.Pointer) {
if buf.lr != 0 {
throw("invalid use of gostartcall")
}
buf.lr = buf.pc
buf.pc = uintptr(fn)
buf.ctxt = ctxt
}
// Called to rewind context saved during morestack back to beginning of function.
// To help us, the linker emits a jmp back to the beginning right after the
// call to morestack. We just have to decode and apply that jump.
func rewindmorestack(buf *gobuf) {
var inst uint64
if buf.pc&1 == 0 && buf.pc != 0 {
inst = *(*uint64)(unsafe.Pointer(buf.pc))
switch inst >> 48 {
case 0xa7f4: // BRC (branch relative on condition) instruction.
inst >>= 32
inst &= 0xFFFF
offset := int64(int16(inst))
offset <<= 1
buf.pc += uintptr(offset)
return
case 0xc0f4: // BRCL (branch relative on condition long) instruction.
inst >>= 16
inst = inst & 0xFFFFFFFF
inst = (inst << 1) & 0xFFFFFFFF
buf.pc += uintptr(int32(inst))
return
}
}
print("runtime: pc=", hex(buf.pc), " ", hex(inst), "\n")
throw("runtime: misuse of rewindmorestack")
}
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