1 // Copyright 2013 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 // +build amd64 amd64p32 386 6 7 package runtime 8 9 import "unsafe" 10 11 // adjust Gobuf as it if executed a call to fn with context ctxt 12 // and then did an immediate gosave. 13 func gostartcall(buf *gobuf, fn, ctxt unsafe.Pointer) { 14 sp := buf.sp 15 if regSize > ptrSize { 16 sp -= ptrSize 17 *(*uintptr)(unsafe.Pointer(sp)) = 0 18 } 19 sp -= ptrSize 20 *(*uintptr)(unsafe.Pointer(sp)) = buf.pc 21 buf.sp = sp 22 buf.pc = uintptr(fn) 23 buf.ctxt = ctxt 24 } 25 26 // Called to rewind context saved during morestack back to beginning of function. 27 // To help us, the linker emits a jmp back to the beginning right after the 28 // call to morestack. We just have to decode and apply that jump. 29 func rewindmorestack(buf *gobuf) { 30 pc := (*[8]byte)(unsafe.Pointer(buf.pc)) 31 if pc[0] == 0xe9 { // jmp 4-byte offset 32 buf.pc = buf.pc + 5 + uintptr(int64(*(*int32)(unsafe.Pointer(&pc[1])))) 33 return 34 } 35 if pc[0] == 0xeb { // jmp 1-byte offset 36 buf.pc = buf.pc + 2 + uintptr(int64(*(*int8)(unsafe.Pointer(&pc[1])))) 37 return 38 } 39 if pc[0] == 0xcc { 40 // This is a breakpoint inserted by gdb. We could use 41 // runtimefindfunc to find the function. But if we 42 // do that, then we will continue execution at the 43 // function entry point, and we will not hit the gdb 44 // breakpoint. So for this case we don't change 45 // buf.pc, so that when we return we will execute 46 // the jump instruction and carry on. This means that 47 // stack unwinding may not work entirely correctly 48 // (https://golang.org/issue/5723) but the user is 49 // running under gdb anyhow. 50 return 51 } 52 print("runtime: pc=", pc, " ", hex(pc[0]), " ", hex(pc[1]), " ", hex(pc[2]), " ", hex(pc[3]), " ", hex(pc[4]), "\n") 53 throw("runtime: misuse of rewindmorestack") 54 } 55
