go/src/pkg/runtime/rt0_linux_arm.s

// Copyright 2009 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.

TEXT _rt0_arm_linux(SB),7,$-4
	// We first need to detect the kernel ABI, and warn the user
	// if the system only supports OABI
	// The strategy here is to call some EABI syscall to see if
	// SIGILL is received.
	// To catch SIGILL, we have to first setup sigaction, this is
	// a chicken-and-egg problem, because we can't do syscall if
	// we don't know the kernel ABI... Oh, not really, we can do
	// syscall in Thumb mode.

	// set up sa_handler
	MOVW	$bad_abi<>(SB), R0 // sa_handler
	MOVW	$0, R1 // sa_flags
	MOVW	$0, R2 // sa_restorer
	MOVW	$0, R3 // sa_mask
	MOVM.DB.W [R0-R3], (R13)
	MOVW	$4, R0 // SIGILL
	MOVW	R13, R1 // sa
	SUB	$16, R13
	MOVW	R13, R2 // old_sa
	MOVW	$8, R3 // c
	MOVW	$174, R7 // sys_sigaction
	BL	oabi_syscall<>(SB)

	// do an EABI syscall
	MOVW	$20, R7 // sys_getpid
	SWI	$0 // this will trigger SIGILL on OABI systems
	
	MOVW	$4, R0  // SIGILL
	MOVW	R13, R1 // sa
	MOVW	$0, R2 // old_sa
	MOVW	$8, R3 // c
	MOVW	$174, R7 // sys_sigaction
	SWI	$0 // restore signal handler
	ADD	$32, R13
	B	_rt0_arm(SB)

TEXT bad_abi<>(SB),7,$-4
	// give diagnosis and exit
	MOVW	$2, R0 // stderr
	MOVW	$bad_abi_msg(SB), R1 // data
	MOVW	$45, R2 // len
	MOVW	$4, R7 // sys_write
	BL	oabi_syscall<>(SB)
	MOVW	$1, R0
	MOVW	$1, R7 // sys_exit
	BL	oabi_syscall<>(SB)
	B  	0(PC)

DATA bad_abi_msg+0x00(SB)/8, $"This pro"
DATA bad_abi_msg+0x08(SB)/8, $"gram can"
DATA bad_abi_msg+0x10(SB)/8, $" only be"
DATA bad_abi_msg+0x18(SB)/8, $" run on "
DATA bad_abi_msg+0x20(SB)/8, $"EABI ker"
DATA bad_abi_msg+0x28(SB)/4, $"nels"
DATA bad_abi_msg+0x2c(SB)/1, $0xa
GLOBL bad_abi_msg(SB), $45

TEXT oabi_syscall<>(SB),7,$-4
	ADD $1, PC, R4
	WORD $0xe12fff14 //BX	(R4) // enter thumb mode
	// TODO(minux): only supports little-endian CPUs
	WORD $0x4770df01 // swi $1; bx lr