1  /*
       2   * Copyright (c) 2003 Russell King <rmk@arm.linux.org.uk>
       3   * Copyright (c) 2011-2013 Denys Vlasenko <vda.linux@googlemail.com>
       4   * Copyright (c) 2011-2015 Dmitry V. Levin <ldv@strace.io>
       5   * Copyright (c) 2015-2021 The strace developers.
       6   * All rights reserved.
       7   *
       8   * SPDX-License-Identifier: LGPL-2.1-or-later
       9   */
      10  
      11  /* Return codes: 1 - ok, 0 - ignore, other - error. */
      12  static int
      13  arch_get_scno(struct tcb *tcp)
      14  {
      15  	kernel_ulong_t scno = 0;
      16  
      17  	/* Note: we support only 32-bit CPUs, not 26-bit */
      18  
      19  #if !defined(__ARM_EABI__) || ENABLE_ARM_OABI
      20  	if (arm_regs.ARM_cpsr & 0x20) {
      21  		/* Thumb mode */
      22  		goto scno_in_r7;
      23  	}
      24  	/* ARM mode */
      25  	/* Check EABI/OABI by examining SVC insn's low 24 bits */
      26  	errno = 0;
      27  	scno = ptrace(PTRACE_PEEKTEXT, tcp->pid, (void *)(arm_regs.ARM_pc - 4), NULL);
      28  	if (errno)
      29  		return -1;
      30  	/* EABI syscall convention? */
      31  	if (scno != 0xef000000) {
      32  		/* No, it's OABI */
      33  		if ((scno & 0x0ff00000) != 0x0f900000) {
      34  			error_msg("pid %d unknown syscall trap 0x%08lx",
      35  				tcp->pid, scno);
      36  			return -1;
      37  		}
      38  		/* Fixup the syscall number */
      39  		scno &= 0x000fffff;
      40  	} else {
      41  scno_in_r7:
      42  		scno = arm_regs.ARM_r7;
      43  	}
      44  #else /* __ARM_EABI__ || !ENABLE_ARM_OABI */
      45  
      46  	scno = arm_regs.ARM_r7;
      47  
      48  #endif
      49  
      50  	/*
      51  	 * Do some sanity checks to figure out
      52  	 * whether it's really a syscall entry.
      53  	 */
      54  	if (arm_regs.ARM_ip && !scno_in_range(scno)) {
      55  		debug_msg("pid %d stray syscall exit: ARM_ip = %ld, scno = %ld",
      56  			  tcp->pid, arm_regs.ARM_ip, scno);
      57  		return 0;
      58  	}
      59  
      60  	tcp->scno = scno;
      61  	return 1;
      62  }