safe-syscall.inc.S (2552B)
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 linux-user/safe-syscall.S 5 * 6 * Written by Richard Henderson <rth@twiddle.net> 7 * Copyright (C) 2016 Red Hat, 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 /* This is the entry point for making a system call. The calling 21 * convention here is that of a C varargs function with the 22 * first argument an 'int *' to the signal_pending flag, the 23 * second one the system call number (as a 'long'), and all further 24 * arguments being syscall arguments (also 'long'). 25 * We return a long which is the syscall's return value, which 26 * may be negative-errno on failure. Conversion to the 27 * -1-and-errno-set convention is done by the calling wrapper. 28 */ 29safe_syscall_base: 30 .cfi_startproc 31 /* The syscall calling convention isn't the same as the 32 * C one: 33 * we enter with x0 == *signal_pending 34 * x1 == syscall number 35 * x2 ... x7, (stack) == syscall arguments 36 * and return the result in x0 37 * and the syscall instruction needs 38 * x8 == syscall number 39 * x0 ... x6 == syscall arguments 40 * and returns the result in x0 41 * Shuffle everything around appropriately. 42 */ 43 mov x9, x0 /* signal_pending pointer */ 44 mov x8, x1 /* syscall number */ 45 mov x0, x2 /* syscall arguments */ 46 mov x1, x3 47 mov x2, x4 48 mov x3, x5 49 mov x4, x6 50 mov x5, x7 51 ldr x6, [sp] 52 53 /* This next sequence of code works in conjunction with the 54 * rewind_if_safe_syscall_function(). If a signal is taken 55 * and the interrupted PC is anywhere between 'safe_syscall_start' 56 * and 'safe_syscall_end' then we rewind it to 'safe_syscall_start'. 57 * The code sequence must therefore be able to cope with this, and 58 * the syscall instruction must be the final one in the sequence. 59 */ 60safe_syscall_start: 61 /* if signal_pending is non-zero, don't do the call */ 62 ldr w10, [x9] 63 cbnz w10, 0f 64 svc 0x0 65safe_syscall_end: 66 /* code path for having successfully executed the syscall */ 67 ret 68 690: 70 /* code path when we didn't execute the syscall */ 71 mov x0, #-TARGET_ERESTARTSYS 72 ret 73 .cfi_endproc 74 75 .size safe_syscall_base, .-safe_syscall_base