util: Add a semihosting implementation to the aarch64 m5 utility.

This will allow it to work on CPUs that only support semihosting like
ARM's fastmodels.

Change-Id: I74e536d79d0f77b864e1e4b9d73e265b6d0b1fcb
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/27245
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

util/m5/src/aarch64/SConsopts

@@ -30,3 +30,4 @@ get_variant_opt('CROSS_COMPILE', 'aarch64-linux-gnu-')
 
 env['CALL_TYPE']['inst'].impl('m5op.S', default=True)
 env['CALL_TYPE']['addr'].impl('m5op_addr.S')
+env['CALL_TYPE']['semi'].impl('m5op_semi.S')

util/m5/src/aarch64/m5op_semi.S

@@ -0,0 +1,91 @@
+/*
+ * Copyright (c) 2010-2013, 2016-2017 ARM Limited
+ * All rights reserved
+ *
+ * The license below extends only to copyright in the software and shall
+ * not be construed as granting a license to any other intellectual
+ * property including but not limited to intellectual property relating
+ * to a hardware implementation of the functionality of the software
+ * licensed hereunder.  You may use the software subject to the license
+ * terms below provided that you ensure that this notice is replicated
+ * unmodified and in its entirety in all distributions of the software,
+ * modified or unmodified, in source code or in binary form.
+ *
+ * Copyright (c) 2003-2006 The Regents of The University of Michigan
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <gem5/asm/generic/m5ops.h>
+
+.macro	m5op_func, name, func
+        .globl \name
+        \name:
+        // Put the m5 op number in x16.
+        mov x16, #(\func << 8)
+        // Branch into the common handler for the rest.
+        b 1f
+.endm
+
+.text
+#define M5OP(name, func) m5op_func M5OP_MERGE_TOKENS(name, _semi), func;
+        M5OP_FOREACH
+#undef M5OP
+
+        1:
+        // Get the address of the argument block.
+        ldr x17, =m5_semi_argument_block
+        // Store the m5 op number in the first slot.
+        str x16, [ x17 ], #8
+        // Store all 8 possible arguments in the subsequent slots. We don't
+        // know how many we need, so just store them all.
+        str x0, [ x17 ], #8
+        str x1, [ x17 ], #8
+        str x2, [ x17 ], #8
+        str x3, [ x17 ], #8
+        str x4, [ x17 ], #8
+        str x5, [ x17 ], #8
+        str x6, [ x17 ], #8
+        str x7, [ x17 ], #8
+        // Set x0 to the m5 op semi-hosting call number.
+        mov x0, #0x100
+        // Set x1 to the address of the argument blob.
+        ldr x1, =m5_semi_argument_block
+        // Trigger the semihosting call with the gem5 specific immediate.
+        hlt #0x5d57
+        ret
+
+.data
+        .globl m5_semi_argument_block
+        m5_semi_argument_block:
+        .quad 0 // function
+        .quad 0 // argument 0
+        .quad 0 // argument 1
+        .quad 0 // argument 2
+        .quad 0 // argument 3
+        .quad 0 // argument 4
+        .quad 0 // argument 5
+        .quad 0 // argument 6
+        .quad 0 // argument 7