| /* |
| * safe-syscall.inc.S : host-specific assembly fragment |
| * to handle signals occurring at the same time as system calls. |
| * This is intended to be included by common-user/safe-syscall.S |
| * |
| * Written by Richard Henderson <rth@twiddle.net> |
| * Copyright (C) 2018 Linaro, Inc. |
| * |
| * This work is licensed under the terms of the GNU GPL, version 2 or later. |
| * See the COPYING file in the top-level directory. |
| */ |
| |
| .global safe_syscall_base |
| .global safe_syscall_start |
| .global safe_syscall_end |
| .type safe_syscall_base, @function |
| .type safe_syscall_start, @function |
| .type safe_syscall_end, @function |
| |
| /* |
| * This is the entry point for making a system call. The calling |
| * convention here is that of a C varargs function with the |
| * first argument an 'int *' to the signal_pending flag, the |
| * second one the system call number (as a 'long'), and all further |
| * arguments being syscall arguments (also 'long'). |
| */ |
| safe_syscall_base: |
| .cfi_startproc |
| /* |
| * The syscall calling convention is nearly the same as C: |
| * we enter with a0 == &signal_pending |
| * a1 == syscall number |
| * a2 ... a7 == syscall arguments |
| * and return the result in a0 |
| * and the syscall instruction needs |
| * a7 == syscall number |
| * a0 ... a5 == syscall arguments |
| * and returns the result in a0 |
| * Shuffle everything around appropriately. |
| */ |
| mv t0, a0 /* signal_pending pointer */ |
| mv t1, a1 /* syscall number */ |
| mv a0, a2 /* syscall arguments */ |
| mv a1, a3 |
| mv a2, a4 |
| mv a3, a5 |
| mv a4, a6 |
| mv a5, a7 |
| mv a7, t1 |
| |
| /* |
| * This next sequence of code works in conjunction with the |
| * rewind_if_safe_syscall_function(). If a signal is taken |
| * and the interrupted PC is anywhere between 'safe_syscall_start' |
| * and 'safe_syscall_end' then we rewind it to 'safe_syscall_start'. |
| * The code sequence must therefore be able to cope with this, and |
| * the syscall instruction must be the final one in the sequence. |
| */ |
| safe_syscall_start: |
| /* If signal_pending is non-zero, don't do the call */ |
| lw t1, 0(t0) |
| bnez t1, 2f |
| scall |
| safe_syscall_end: |
| /* code path for having successfully executed the syscall */ |
| li t2, -4096 |
| bgtu a0, t2, 0f |
| ret |
| |
| /* code path setting errno */ |
| 0: neg a0, a0 |
| j safe_syscall_set_errno_tail |
| |
| /* code path when we didn't execute the syscall */ |
| 2: li a0, QEMU_ERESTARTSYS |
| j safe_syscall_set_errno_tail |
| |
| .cfi_endproc |
| .size safe_syscall_base, .-safe_syscall_base |