signal_ios_arm64.s

     1  // Copyright 2015 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  #include "textflag.h"
     6  
     7  // xx_cgo_panicmem is the entrypoint for SIGSEGV as intercepted via a
     8  // mach thread port as EXC_BAD_ACCESS. As the segfault may have happened
     9  // in C code, we first need to load_g then call xx_cgo_panicmem.
    10  //
    11  //	R1 - LR at moment of fault
    12  //	R2 - PC at moment of fault
    13  TEXT xx_cgo_panicmem(SB),NOSPLIT|NOFRAME,$0
    14  	// If in external C code, we need to load the g register.
    15  	BL  runtime·load_g(SB)
    16  	CMP $0, g
    17  	BNE ongothread
    18  
    19  	// On a foreign thread.
    20  	// TODO(crawshaw): call badsignal
    21  	MOVD.W $0, -16(RSP)
    22  	MOVW $139, R1
    23  	MOVW R1, 8(RSP)
    24  	B    runtime·exit(SB)
    25  
    26  ongothread:
    27  	// Trigger a SIGSEGV panic.
    28  	//
    29  	// The goal is to arrange the stack so it looks like the runtime
    30  	// function sigpanic was called from the PC that faulted. It has
    31  	// to be sigpanic, as the stack unwinding code in traceback.go
    32  	// looks explicitly for it.
    33  	//
    34  	// To do this we call into runtime·setsigsegv, which sets the
    35  	// appropriate state inside the g object. We give it the faulting
    36  	// PC on the stack, then put it in the LR before calling sigpanic.
    37  
    38  	// Build a 32-byte stack frame for us for this call.
    39  	// Saved LR (none available) is at the bottom,
    40  	// then the PC argument for setsigsegv,
    41  	// then a copy of the LR for us to restore.
    42  	MOVD.W $0, -32(RSP)
    43  	MOVD R1, 8(RSP)
    44  	MOVD R2, 16(RSP)
    45  	BL runtime·setsigsegv(SB)
    46  	MOVD 8(RSP), R1
    47  	MOVD 16(RSP), R2
    48  
    49  	// Build a 16-byte stack frame for the simulated
    50  	// call to sigpanic, by taking 16 bytes away from the
    51  	// 32-byte stack frame above.
    52  	// The saved LR in this frame is the LR at time of fault,
    53  	// and the LR on entry to sigpanic is the PC at time of fault.
    54  	MOVD.W R1, 16(RSP)
    55  	MOVD R2, R30
    56  	B runtime·sigpanic(SB)
    57
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