safe-syscall.inc.S (3543B)
1 /* 2 * safe-syscall.inc.S : host-specific assembly fragment 3 * to handle signals occurring at the same time as system calls. 4 * This is intended to be included by common-user/safe-syscall.S 5 * 6 * Ported to LoongArch by WANG Xuerui <git@xen0n.name> 7 * 8 * Based on safe-syscall.inc.S code for RISC-V, 9 * originally written by Richard Henderson <rth@twiddle.net> 10 * Copyright (C) 2018 Linaro, Inc. 11 * 12 * This work is licensed under the terms of the GNU GPL, version 2 or later. 13 * See the COPYING file in the top-level directory. 14 */ 15 16 .global safe_syscall_base 17 .global safe_syscall_start 18 .global safe_syscall_end 19 .type safe_syscall_base, @function 20 .type safe_syscall_start, @function 21 .type safe_syscall_end, @function 22 23 /* 24 * This is the entry point for making a system call. The calling 25 * convention here is that of a C varargs function with the 26 * first argument an 'int *' to the signal_pending flag, the 27 * second one the system call number (as a 'long'), and all further 28 * arguments being syscall arguments (also 'long'). 29 */ 30 safe_syscall_base: 31 .cfi_startproc 32 /* 33 * The syscall calling convention is nearly the same as C: 34 * we enter with a0 == &signal_pending 35 * a1 == syscall number 36 * a2 ... a7 == syscall arguments 37 * and return the result in a0 38 * and the syscall instruction needs 39 * a7 == syscall number 40 * a0 ... a5 == syscall arguments 41 * and returns the result in a0 42 * Shuffle everything around appropriately. 43 */ 44 move $t0, $a0 /* signal_pending pointer */ 45 move $t1, $a1 /* syscall number */ 46 move $a0, $a2 /* syscall arguments */ 47 move $a1, $a3 48 move $a2, $a4 49 move $a3, $a5 50 move $a4, $a6 51 move $a5, $a7 52 move $a7, $t1 53 54 /* 55 * We need to preserve the signal_pending pointer but t0 is 56 * clobbered by syscalls on LoongArch, so we need to move it 57 * somewhere else, ideally both preserved across syscalls and 58 * clobbered by procedure calls so we don't have to allocate a 59 * stack frame; a6 is just the register we want here. 60 */ 61 move $a6, $t0 62 63 /* 64 * This next sequence of code works in conjunction with the 65 * rewind_if_safe_syscall_function(). If a signal is taken 66 * and the interrupted PC is anywhere between 'safe_syscall_start' 67 * and 'safe_syscall_end' then we rewind it to 'safe_syscall_start'. 68 * The code sequence must therefore be able to cope with this, and 69 * the syscall instruction must be the final one in the sequence. 70 */ 71 safe_syscall_start: 72 /* If signal_pending is non-zero, don't do the call */ 73 ld.w $t1, $a6, 0 74 bnez $t1, 2f 75 syscall 0 76 safe_syscall_end: 77 /* code path for having successfully executed the syscall */ 78 li.w $t2, -4096 79 bgtu $a0, $t2, 0f 80 jr $ra 81 82 /* code path setting errno */ 83 0: sub.d $a0, $zero, $a0 84 b safe_syscall_set_errno_tail 85 86 /* code path when we didn't execute the syscall */ 87 2: li.w $a0, QEMU_ERESTARTSYS 88 b safe_syscall_set_errno_tail 89 .cfi_endproc 90 .size safe_syscall_base, .-safe_syscall_base