1*b8c92c6dSRichard Henderson/* 2*b8c92c6dSRichard Henderson * safe-syscall.inc.S : host-specific assembly fragment 3*b8c92c6dSRichard Henderson * to handle signals occurring at the same time as system calls. 4*b8c92c6dSRichard Henderson * This is intended to be included by linux-user/safe-syscall.S 5*b8c92c6dSRichard Henderson * 6*b8c92c6dSRichard Henderson * Written by Richard Henderson <rth@twiddle.net> 7*b8c92c6dSRichard Henderson * Copyright (C) 2018 Linaro, Inc. 8*b8c92c6dSRichard Henderson * 9*b8c92c6dSRichard Henderson * This work is licensed under the terms of the GNU GPL, version 2 or later. 10*b8c92c6dSRichard Henderson * See the COPYING file in the top-level directory. 11*b8c92c6dSRichard Henderson */ 12*b8c92c6dSRichard Henderson 13*b8c92c6dSRichard Henderson .global safe_syscall_base 14*b8c92c6dSRichard Henderson .global safe_syscall_start 15*b8c92c6dSRichard Henderson .global safe_syscall_end 16*b8c92c6dSRichard Henderson .type safe_syscall_base, @function 17*b8c92c6dSRichard Henderson .type safe_syscall_start, @function 18*b8c92c6dSRichard Henderson .type safe_syscall_end, @function 19*b8c92c6dSRichard Henderson 20*b8c92c6dSRichard Henderson /* 21*b8c92c6dSRichard Henderson * This is the entry point for making a system call. The calling 22*b8c92c6dSRichard Henderson * convention here is that of a C varargs function with the 23*b8c92c6dSRichard Henderson * first argument an 'int *' to the signal_pending flag, the 24*b8c92c6dSRichard Henderson * second one the system call number (as a 'long'), and all further 25*b8c92c6dSRichard Henderson * arguments being syscall arguments (also 'long'). 26*b8c92c6dSRichard Henderson * We return a long which is the syscall's return value, which 27*b8c92c6dSRichard Henderson * may be negative-errno on failure. Conversion to the 28*b8c92c6dSRichard Henderson * -1-and-errno-set convention is done by the calling wrapper. 29*b8c92c6dSRichard Henderson */ 30*b8c92c6dSRichard Hendersonsafe_syscall_base: 31*b8c92c6dSRichard Henderson .cfi_startproc 32*b8c92c6dSRichard Henderson /* 33*b8c92c6dSRichard Henderson * The syscall calling convention is nearly the same as C: 34*b8c92c6dSRichard Henderson * we enter with a0 == *signal_pending 35*b8c92c6dSRichard Henderson * a1 == syscall number 36*b8c92c6dSRichard Henderson * a2 ... a7 == syscall arguments 37*b8c92c6dSRichard Henderson * and return the result in a0 38*b8c92c6dSRichard Henderson * and the syscall instruction needs 39*b8c92c6dSRichard Henderson * a7 == syscall number 40*b8c92c6dSRichard Henderson * a0 ... a5 == syscall arguments 41*b8c92c6dSRichard Henderson * and returns the result in a0 42*b8c92c6dSRichard Henderson * Shuffle everything around appropriately. 43*b8c92c6dSRichard Henderson */ 44*b8c92c6dSRichard Henderson mv t0, a0 /* signal_pending pointer */ 45*b8c92c6dSRichard Henderson mv t1, a1 /* syscall number */ 46*b8c92c6dSRichard Henderson mv a0, a2 /* syscall arguments */ 47*b8c92c6dSRichard Henderson mv a1, a3 48*b8c92c6dSRichard Henderson mv a2, a4 49*b8c92c6dSRichard Henderson mv a3, a5 50*b8c92c6dSRichard Henderson mv a4, a6 51*b8c92c6dSRichard Henderson mv a5, a7 52*b8c92c6dSRichard Henderson mv a7, t1 53*b8c92c6dSRichard Henderson 54*b8c92c6dSRichard Henderson /* 55*b8c92c6dSRichard Henderson * This next sequence of code works in conjunction with the 56*b8c92c6dSRichard Henderson * rewind_if_safe_syscall_function(). If a signal is taken 57*b8c92c6dSRichard Henderson * and the interrupted PC is anywhere between 'safe_syscall_start' 58*b8c92c6dSRichard Henderson * and 'safe_syscall_end' then we rewind it to 'safe_syscall_start'. 59*b8c92c6dSRichard Henderson * The code sequence must therefore be able to cope with this, and 60*b8c92c6dSRichard Henderson * the syscall instruction must be the final one in the sequence. 61*b8c92c6dSRichard Henderson */ 62*b8c92c6dSRichard Hendersonsafe_syscall_start: 63*b8c92c6dSRichard Henderson /* If signal_pending is non-zero, don't do the call */ 64*b8c92c6dSRichard Henderson lw t1, 0(t0) 65*b8c92c6dSRichard Henderson bnez t1, 0f 66*b8c92c6dSRichard Henderson scall 67*b8c92c6dSRichard Hendersonsafe_syscall_end: 68*b8c92c6dSRichard Henderson /* code path for having successfully executed the syscall */ 69*b8c92c6dSRichard Henderson ret 70*b8c92c6dSRichard Henderson 71*b8c92c6dSRichard Henderson0: 72*b8c92c6dSRichard Henderson /* code path when we didn't execute the syscall */ 73*b8c92c6dSRichard Henderson li a0, -TARGET_ERESTARTSYS 74*b8c92c6dSRichard Henderson ret 75*b8c92c6dSRichard Henderson .cfi_endproc 76*b8c92c6dSRichard Henderson 77*b8c92c6dSRichard Henderson .size safe_syscall_base, .-safe_syscall_base 78