safe-syscall.inc.S (2998B)
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 * Written by Richard Henderson <rth@twiddle.net> 7 * Copyright (C) 2018 Linaro, Inc. 8 * 9 * This work is licensed under the terms of the GNU GPL, version 2 or later. 10 * See the COPYING file in the top-level directory. 11 */ 12 13 .global safe_syscall_base 14 .global safe_syscall_start 15 .global safe_syscall_end 16 .type safe_syscall_base, @function 17 .type safe_syscall_start, @function 18 .type safe_syscall_end, @function 19 20 /* 21 * This is the entry point for making a system call. The calling 22 * convention here is that of a C varargs function with the 23 * first argument an 'int *' to the signal_pending flag, the 24 * second one the system call number (as a 'long'), and all further 25 * arguments being syscall arguments (also 'long'). 26 */ 27 safe_syscall_base: 28 .cfi_startproc 29 /* 30 * The syscall calling convention is nearly the same as C: 31 * we enter with a0 == &signal_pending 32 * a1 == syscall number 33 * a2 ... a7 == syscall arguments 34 * and return the result in a0 35 * and the syscall instruction needs 36 * a7 == syscall number 37 * a0 ... a5 == syscall arguments 38 * and returns the result in a0 39 * Shuffle everything around appropriately. 40 */ 41 mv t0, a0 /* signal_pending pointer */ 42 mv t1, a1 /* syscall number */ 43 mv a0, a2 /* syscall arguments */ 44 mv a1, a3 45 mv a2, a4 46 mv a3, a5 47 mv a4, a6 48 mv a5, a7 49 mv a7, t1 50 51 /* 52 * This next sequence of code works in conjunction with the 53 * rewind_if_safe_syscall_function(). If a signal is taken 54 * and the interrupted PC is anywhere between 'safe_syscall_start' 55 * and 'safe_syscall_end' then we rewind it to 'safe_syscall_start'. 56 * The code sequence must therefore be able to cope with this, and 57 * the syscall instruction must be the final one in the sequence. 58 */ 59 safe_syscall_start: 60 /* If signal_pending is non-zero, don't do the call */ 61 lw t1, 0(t0) 62 bnez t1, 2f 63 scall 64 safe_syscall_end: 65 /* code path for having successfully executed the syscall */ 66 li t2, -4096 67 bgtu a0, t2, 0f 68 ret 69 70 /* code path setting errno */ 71 0: neg a0, a0 72 j safe_syscall_set_errno_tail 73 74 /* code path when we didn't execute the syscall */ 75 2: li a0, QEMU_ERESTARTSYS 76 j safe_syscall_set_errno_tail 77 78 .cfi_endproc 79 .size safe_syscall_base, .-safe_syscall_base