diff options
Diffstat (limited to 'common-user/host/aarch64/safe-syscall.inc.S')
| -rw-r--r-- | common-user/host/aarch64/safe-syscall.inc.S | 88 |
1 files changed, 88 insertions, 0 deletions
diff --git a/common-user/host/aarch64/safe-syscall.inc.S b/common-user/host/aarch64/safe-syscall.inc.S new file mode 100644 index 0000000000..b8fd5b553e --- /dev/null +++ b/common-user/host/aarch64/safe-syscall.inc.S @@ -0,0 +1,88 @@ +/* + * safe-syscall.inc.S : host-specific assembly fragment + * to handle signals occurring at the same time as system calls. + * This is intended to be included by common-user/safe-syscall.S + * + * Written by Richard Henderson <rth@twiddle.net> + * Copyright (C) 2016 Red Hat, Inc. + * + * This work is licensed under the terms of the GNU GPL, version 2 or later. + * See the COPYING file in the top-level directory. + */ + + .global safe_syscall_base + .global safe_syscall_start + .global safe_syscall_end + .type safe_syscall_base, #function + .type safe_syscall_start, #function + .type safe_syscall_end, #function + + /* This is the entry point for making a system call. The calling + * convention here is that of a C varargs function with the + * first argument an 'int *' to the signal_pending flag, the + * second one the system call number (as a 'long'), and all further + * arguments being syscall arguments (also 'long'). + */ +safe_syscall_base: + .cfi_startproc + /* The syscall calling convention isn't the same as the + * C one: + * we enter with x0 == &signal_pending + * x1 == syscall number + * x2 ... x7, (stack) == syscall arguments + * and return the result in x0 + * and the syscall instruction needs + * x8 == syscall number + * x0 ... x6 == syscall arguments + * and returns the result in x0 + * Shuffle everything around appropriately. + */ + mov x9, x0 /* signal_pending pointer */ + mov x8, x1 /* syscall number */ + mov x0, x2 /* syscall arguments */ + mov x1, x3 + mov x2, x4 + mov x3, x5 + mov x4, x6 + mov x5, x7 + ldr x6, [sp] + + /* This next sequence of code works in conjunction with the + * rewind_if_safe_syscall_function(). If a signal is taken + * and the interrupted PC is anywhere between 'safe_syscall_start' + * and 'safe_syscall_end' then we rewind it to 'safe_syscall_start'. + * The code sequence must therefore be able to cope with this, and + * the syscall instruction must be the final one in the sequence. + */ +safe_syscall_start: + /* if signal_pending is non-zero, don't do the call */ + ldr w10, [x9] + cbnz w10, 2f + svc 0x0 +safe_syscall_end: + + /* code path for having successfully executed the syscall */ +#if defined(__linux__) + /* Linux kernel returns (small) negative errno. */ + cmp x0, #-4096 + b.hi 0f +#elif defined(__FreeBSD__) + /* FreeBSD kernel returns positive errno and C bit set. */ + b.cs 1f +#else +#error "unsupported os" +#endif + ret + +#if defined(__linux__) + /* code path setting errno */ +0: neg w0, w0 + b safe_syscall_set_errno_tail +#endif + + /* code path when we didn't execute the syscall */ +2: mov w0, #QEMU_ERESTARTSYS +1: b safe_syscall_set_errno_tail + + .cfi_endproc + .size safe_syscall_base, .-safe_syscall_base |