1*bbf15aafSRichard Henderson/* 2*bbf15aafSRichard Henderson * safe-syscall.inc.S : host-specific assembly fragment 3*bbf15aafSRichard Henderson * to handle signals occurring at the same time as system calls. 4*bbf15aafSRichard Henderson * This is intended to be included by common-user/safe-syscall.S 5*bbf15aafSRichard Henderson * 6*bbf15aafSRichard Henderson * Copyright (C) 2015 Timothy Edward Baldwin <T.E.Baldwin99@members.leeds.ac.uk> 7*bbf15aafSRichard Henderson * 8*bbf15aafSRichard Henderson * This work is licensed under the terms of the GNU GPL, version 2 or later. 9*bbf15aafSRichard Henderson * See the COPYING file in the top-level directory. 10*bbf15aafSRichard Henderson */ 11*bbf15aafSRichard Henderson 12*bbf15aafSRichard Henderson .global safe_syscall_base 13*bbf15aafSRichard Henderson .global safe_syscall_start 14*bbf15aafSRichard Henderson .global safe_syscall_end 15*bbf15aafSRichard Henderson .type safe_syscall_base, @function 16*bbf15aafSRichard Henderson 17*bbf15aafSRichard Henderson /* This is the entry point for making a system call. The calling 18*bbf15aafSRichard Henderson * convention here is that of a C varargs function with the 19*bbf15aafSRichard Henderson * first argument an 'int *' to the signal_pending flag, the 20*bbf15aafSRichard Henderson * second one the system call number (as a 'long'), and all further 21*bbf15aafSRichard Henderson * arguments being syscall arguments (also 'long'). 22*bbf15aafSRichard Henderson */ 23*bbf15aafSRichard Hendersonsafe_syscall_base: 24*bbf15aafSRichard Henderson .cfi_startproc 25*bbf15aafSRichard Henderson /* This saves a frame pointer and aligns the stack for the syscall. 26*bbf15aafSRichard Henderson * (It's unclear if the syscall ABI has the same stack alignment 27*bbf15aafSRichard Henderson * requirements as the userspace function call ABI, but better safe than 28*bbf15aafSRichard Henderson * sorry. Appendix A2 of http://www.x86-64.org/documentation/abi.pdf 29*bbf15aafSRichard Henderson * does not list any ABI differences regarding stack alignment.) 30*bbf15aafSRichard Henderson */ 31*bbf15aafSRichard Henderson push %rbp 32*bbf15aafSRichard Henderson .cfi_adjust_cfa_offset 8 33*bbf15aafSRichard Henderson .cfi_rel_offset rbp, 0 34*bbf15aafSRichard Henderson 35*bbf15aafSRichard Henderson /* 36*bbf15aafSRichard Henderson * The syscall calling convention isn't the same as the C one: 37*bbf15aafSRichard Henderson * we enter with rdi == &signal_pending 38*bbf15aafSRichard Henderson * rsi == syscall number 39*bbf15aafSRichard Henderson * rdx, rcx, r8, r9, (stack), (stack) == syscall arguments 40*bbf15aafSRichard Henderson * and return the result in rax 41*bbf15aafSRichard Henderson * and the syscall instruction needs 42*bbf15aafSRichard Henderson * rax == syscall number 43*bbf15aafSRichard Henderson * rdi, rsi, rdx, r10, r8, r9 == syscall arguments 44*bbf15aafSRichard Henderson * and returns the result in rax 45*bbf15aafSRichard Henderson * Shuffle everything around appropriately. 46*bbf15aafSRichard Henderson * Note that syscall will trash rcx and r11. 47*bbf15aafSRichard Henderson */ 48*bbf15aafSRichard Henderson mov %rsi, %rax /* syscall number */ 49*bbf15aafSRichard Henderson mov %rdi, %rbp /* signal_pending pointer */ 50*bbf15aafSRichard Henderson /* and the syscall arguments */ 51*bbf15aafSRichard Henderson mov %rdx, %rdi 52*bbf15aafSRichard Henderson mov %rcx, %rsi 53*bbf15aafSRichard Henderson mov %r8, %rdx 54*bbf15aafSRichard Henderson mov %r9, %r10 55*bbf15aafSRichard Henderson mov 16(%rsp), %r8 56*bbf15aafSRichard Henderson mov 24(%rsp), %r9 57*bbf15aafSRichard Henderson 58*bbf15aafSRichard Henderson /* This next sequence of code works in conjunction with the 59*bbf15aafSRichard Henderson * rewind_if_safe_syscall_function(). If a signal is taken 60*bbf15aafSRichard Henderson * and the interrupted PC is anywhere between 'safe_syscall_start' 61*bbf15aafSRichard Henderson * and 'safe_syscall_end' then we rewind it to 'safe_syscall_start'. 62*bbf15aafSRichard Henderson * The code sequence must therefore be able to cope with this, and 63*bbf15aafSRichard Henderson * the syscall instruction must be the final one in the sequence. 64*bbf15aafSRichard Henderson */ 65*bbf15aafSRichard Hendersonsafe_syscall_start: 66*bbf15aafSRichard Henderson /* if signal_pending is non-zero, don't do the call */ 67*bbf15aafSRichard Henderson cmpl $0, (%rbp) 68*bbf15aafSRichard Henderson jnz 2f 69*bbf15aafSRichard Henderson syscall 70*bbf15aafSRichard Hendersonsafe_syscall_end: 71*bbf15aafSRichard Henderson /* code path for having successfully executed the syscall */ 72*bbf15aafSRichard Henderson cmp $-4095, %rax 73*bbf15aafSRichard Henderson jae 0f 74*bbf15aafSRichard Henderson pop %rbp 75*bbf15aafSRichard Henderson .cfi_remember_state 76*bbf15aafSRichard Henderson .cfi_def_cfa_offset 8 77*bbf15aafSRichard Henderson .cfi_restore rbp 78*bbf15aafSRichard Henderson ret 79*bbf15aafSRichard Henderson .cfi_restore_state 80*bbf15aafSRichard Henderson 81*bbf15aafSRichard Henderson0: neg %eax 82*bbf15aafSRichard Henderson jmp 1f 83*bbf15aafSRichard Henderson 84*bbf15aafSRichard Henderson /* code path when we didn't execute the syscall */ 85*bbf15aafSRichard Henderson2: mov $QEMU_ERESTARTSYS, %eax 86*bbf15aafSRichard Henderson 87*bbf15aafSRichard Henderson /* code path setting errno */ 88*bbf15aafSRichard Henderson1: pop %rbp 89*bbf15aafSRichard Henderson .cfi_def_cfa_offset 8 90*bbf15aafSRichard Henderson .cfi_restore rbp 91*bbf15aafSRichard Henderson jmp safe_syscall_set_errno_tail 92*bbf15aafSRichard Henderson .cfi_endproc 93*bbf15aafSRichard Henderson 94*bbf15aafSRichard Henderson .size safe_syscall_base, .-safe_syscall_base 95