1bbf15aafSRichard Henderson/* 2bbf15aafSRichard Henderson * safe-syscall.inc.S : host-specific assembly fragment 3bbf15aafSRichard Henderson * to handle signals occurring at the same time as system calls. 4bbf15aafSRichard Henderson * This is intended to be included by common-user/safe-syscall.S 5bbf15aafSRichard Henderson * 6bbf15aafSRichard Henderson * Copyright (C) 2015 Timothy Edward Baldwin <T.E.Baldwin99@members.leeds.ac.uk> 7bbf15aafSRichard Henderson * 8bbf15aafSRichard Henderson * This work is licensed under the terms of the GNU GPL, version 2 or later. 9bbf15aafSRichard Henderson * See the COPYING file in the top-level directory. 10bbf15aafSRichard Henderson */ 11bbf15aafSRichard Henderson 12bbf15aafSRichard Henderson .global safe_syscall_base 13bbf15aafSRichard Henderson .global safe_syscall_start 14bbf15aafSRichard Henderson .global safe_syscall_end 15bbf15aafSRichard Henderson .type safe_syscall_base, @function 16bbf15aafSRichard Henderson 17bbf15aafSRichard Henderson /* This is the entry point for making a system call. The calling 18bbf15aafSRichard Henderson * convention here is that of a C varargs function with the 19bbf15aafSRichard Henderson * first argument an 'int *' to the signal_pending flag, the 20bbf15aafSRichard Henderson * second one the system call number (as a 'long'), and all further 21bbf15aafSRichard Henderson * arguments being syscall arguments (also 'long'). 22bbf15aafSRichard Henderson */ 23bbf15aafSRichard Hendersonsafe_syscall_base: 24bbf15aafSRichard Henderson .cfi_startproc 25bbf15aafSRichard Henderson /* This saves a frame pointer and aligns the stack for the syscall. 26bbf15aafSRichard Henderson * (It's unclear if the syscall ABI has the same stack alignment 27bbf15aafSRichard Henderson * requirements as the userspace function call ABI, but better safe than 28bbf15aafSRichard Henderson * sorry. Appendix A2 of http://www.x86-64.org/documentation/abi.pdf 29bbf15aafSRichard Henderson * does not list any ABI differences regarding stack alignment.) 30bbf15aafSRichard Henderson */ 31bbf15aafSRichard Henderson push %rbp 32bbf15aafSRichard Henderson .cfi_adjust_cfa_offset 8 33bbf15aafSRichard Henderson .cfi_rel_offset rbp, 0 34bbf15aafSRichard Henderson 35bbf15aafSRichard Henderson /* 36bbf15aafSRichard Henderson * The syscall calling convention isn't the same as the C one: 37bbf15aafSRichard Henderson * we enter with rdi == &signal_pending 38bbf15aafSRichard Henderson * rsi == syscall number 39bbf15aafSRichard Henderson * rdx, rcx, r8, r9, (stack), (stack) == syscall arguments 40bbf15aafSRichard Henderson * and return the result in rax 41bbf15aafSRichard Henderson * and the syscall instruction needs 42bbf15aafSRichard Henderson * rax == syscall number 43bbf15aafSRichard Henderson * rdi, rsi, rdx, r10, r8, r9 == syscall arguments 44bbf15aafSRichard Henderson * and returns the result in rax 45bbf15aafSRichard Henderson * Shuffle everything around appropriately. 46bbf15aafSRichard Henderson * Note that syscall will trash rcx and r11. 47bbf15aafSRichard Henderson */ 48bbf15aafSRichard Henderson mov %rsi, %rax /* syscall number */ 49bbf15aafSRichard Henderson mov %rdi, %rbp /* signal_pending pointer */ 50bbf15aafSRichard Henderson /* and the syscall arguments */ 51bbf15aafSRichard Henderson mov %rdx, %rdi 52bbf15aafSRichard Henderson mov %rcx, %rsi 53bbf15aafSRichard Henderson mov %r8, %rdx 54bbf15aafSRichard Henderson mov %r9, %r10 55bbf15aafSRichard Henderson mov 16(%rsp), %r8 56bbf15aafSRichard Henderson mov 24(%rsp), %r9 57bbf15aafSRichard Henderson 58bbf15aafSRichard Henderson /* This next sequence of code works in conjunction with the 59bbf15aafSRichard Henderson * rewind_if_safe_syscall_function(). If a signal is taken 60bbf15aafSRichard Henderson * and the interrupted PC is anywhere between 'safe_syscall_start' 61bbf15aafSRichard Henderson * and 'safe_syscall_end' then we rewind it to 'safe_syscall_start'. 62bbf15aafSRichard Henderson * The code sequence must therefore be able to cope with this, and 63bbf15aafSRichard Henderson * the syscall instruction must be the final one in the sequence. 64bbf15aafSRichard Henderson */ 65bbf15aafSRichard Hendersonsafe_syscall_start: 66bbf15aafSRichard Henderson /* if signal_pending is non-zero, don't do the call */ 67bbf15aafSRichard Henderson cmpl $0, (%rbp) 68bbf15aafSRichard Henderson jnz 2f 69bbf15aafSRichard Henderson syscall 70bbf15aafSRichard Hendersonsafe_syscall_end: 71*5bfd125eSRichard Henderson 72bbf15aafSRichard Henderson /* code path for having successfully executed the syscall */ 73*5bfd125eSRichard Henderson#if defined(__linux__) 74*5bfd125eSRichard Henderson /* Linux kernel returns (small) negative errno. */ 75bbf15aafSRichard Henderson cmp $-4095, %rax 76bbf15aafSRichard Henderson jae 0f 77*5bfd125eSRichard Henderson#elif defined(__FreeBSD__) 78*5bfd125eSRichard Henderson /* FreeBSD kernel returns positive errno and C bit set. */ 79*5bfd125eSRichard Henderson jc 1f 80*5bfd125eSRichard Henderson#else 81*5bfd125eSRichard Henderson#error "unsupported os" 82*5bfd125eSRichard Henderson#endif 83bbf15aafSRichard Henderson pop %rbp 84bbf15aafSRichard Henderson .cfi_remember_state 85bbf15aafSRichard Henderson .cfi_def_cfa_offset 8 86bbf15aafSRichard Henderson .cfi_restore rbp 87bbf15aafSRichard Henderson ret 88bbf15aafSRichard Henderson .cfi_restore_state 89bbf15aafSRichard Henderson 90*5bfd125eSRichard Henderson#if defined(__linux__) 91bbf15aafSRichard Henderson0: neg %eax 92bbf15aafSRichard Henderson jmp 1f 93*5bfd125eSRichard Henderson#endif 94bbf15aafSRichard Henderson 95bbf15aafSRichard Henderson /* code path when we didn't execute the syscall */ 96bbf15aafSRichard Henderson2: mov $QEMU_ERESTARTSYS, %eax 97bbf15aafSRichard Henderson 98bbf15aafSRichard Henderson /* code path setting errno */ 99bbf15aafSRichard Henderson1: pop %rbp 100bbf15aafSRichard Henderson .cfi_def_cfa_offset 8 101bbf15aafSRichard Henderson .cfi_restore rbp 102bbf15aafSRichard Henderson jmp safe_syscall_set_errno_tail 103bbf15aafSRichard Henderson .cfi_endproc 104bbf15aafSRichard Henderson 105bbf15aafSRichard Henderson .size safe_syscall_base, .-safe_syscall_base 106