xref: /kvm-unit-tests/s390x/snippets/c/cstart.S (revision 2c96b77ec9d3b1fcec7525174e23a6240ee05949)
1/* SPDX-License-Identifier: GPL-2.0-only */
2/*
3 * Start assembly for snippets
4 *
5 * Copyright (c) 2021 IBM Corp.
6 *
7 * Authors:
8 *  Janosch Frank <frankja@linux.ibm.com>
9 */
10#include <asm/sigp.h>
11
12.section .init
13	.globl start
14start:
15	/* XOR all registers with themselves to clear them fully. */
16	.irp i, 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
17	xgr \i,\i
18	.endr
19	/* 0x3000 is the stack page for now */
20	lghi	%r15, stackptr
21	sam64
22	brasl	%r14, main
23	/*
24	 * If main() returns, we stop the CPU with the code below. We also
25	 * route some functions that are required by the libc (but not usable
26	 * from snippets) to the CPU stop code below, so that snippets can
27	 * still be linked against the libc code (to use non-related functions
28	 * like memset() etc.)
29	 */
30.global puts
31.global exit
32puts:
33exit:
34	/* For now let's only use cpu 0 in snippets so this will always work. */
35	xgr	%r0, %r0
36	sigp    %r2, %r0, SIGP_STOP
37