// Copyright 2015 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.

#include "textflag.h"

// xx_cgo_panicmem is the entrypoint for SIGSEGV as intercepted via a

// mach thread port as EXC_BAD_ACCESS. As the segfault may have happened

// in C code, we first need to load_g then call xx_cgo_panicmem.

//

// R1 - LR at moment of fault

// R2 - PC at moment of fault

TEXT xx_cgo_panicmem(SB),NOSPLIT|NOFRAME,$0

// If in external C code, we need to load the g register.

BL runtime·load_g(SB)

CMP $0, g

BNE ongothread

// On a foreign thread.

// TODO(crawshaw): call badsignal

MOVD.W $0, -16(RSP)

MOVW $139, R1

MOVW R1, 8(RSP)

B runtime·exit(SB)

ongothread:

// Trigger a SIGSEGV panic.

//

// The goal is to arrange the stack so it looks like the runtime

// function sigpanic was called from the PC that faulted. It has

// to be sigpanic, as the stack unwinding code in traceback.go

// looks explicitly for it.

//

// To do this we call into runtime·setsigsegv, which sets the

// appropriate state inside the g object. We give it the faulting

// PC on the stack, then put it in the LR before calling sigpanic.

// Build a 32-byte stack frame for us for this call.

// Saved LR (none available) is at the bottom,

// then the PC argument for setsigsegv,

// then a copy of the LR for us to restore.

MOVD.W $0, -32(RSP)

MOVD R1, 8(RSP)

MOVD R2, 16(RSP)

BL runtime·setsigsegv(SB)

MOVD 8(RSP), R1

MOVD 16(RSP), R2

// Build a 16-byte stack frame for the simulated

// call to sigpanic, by taking 16 bytes away from the

// 32-byte stack frame above.

// The saved LR in this frame is the LR at time of fault,

// and the LR on entry to sigpanic is the PC at time of fault.

MOVD.W R1, 16(RSP)

MOVD R2, R30

B runtime·sigpanic(SB)