common-user: Move safe-syscall.* from linux-user

Move linux-user safe-syscall.S and safe-syscall-error.c to common-user
so that bsd-user can also use it.  Also move safe-syscall.h to
include/user/.  Since there is nothing here that is related to the guest,
as opposed to the host, build it once.

Reviewed-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

common-user/host/ppc64/safe-syscall.inc.S

@@ -0,0 +1,94 @@
+/*
+ * 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
+
+        .text
+
+        /* 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').
+         */
+#if _CALL_ELF == 2
+safe_syscall_base:
+        .cfi_startproc
+        .localentry safe_syscall_base,0
+#else
+        .section ".opd","aw"
+        .align  3
+safe_syscall_base:
+        .quad   .L.safe_syscall_base,.TOC.@tocbase,0
+        .previous
+.L.safe_syscall_base:
+        .cfi_startproc
+#endif
+        /* We enter with r3 == &signal_pending
+         *               r4 == syscall number
+         *               r5 ... r10 == syscall arguments
+         *               and return the result in r3
+         * and the syscall instruction needs
+         *               r0 == syscall number
+         *               r3 ... r8 == syscall arguments
+         *               and returns the result in r3
+         * Shuffle everything around appropriately.
+         */
+        std     14, 16(1) /* Preserve r14 in SP+16 */
+        .cfi_offset 14, 16
+        mr      14, 3   /* signal_pending */
+        mr      0, 4    /* syscall number */
+        mr      3, 5    /* syscall arguments */
+        mr      4, 6
+        mr      5, 7
+        mr      6, 8
+        mr      7, 9
+        mr      8, 10
+
+        /* 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 */
+        lwz     12, 0(14)
+        cmpwi   0, 12, 0
+        bne-    2f
+        sc
+safe_syscall_end:
+        /* code path when we did execute the syscall */
+        ld      14, 16(1) /* restore r14 */
+        bso-    1f
+        blr
+
+        /* code path when we didn't execute the syscall */
+2:      ld      14, 16(1) /* restore r14 */
+        addi    3, 0, QEMU_ERESTARTSYS
+
+        /* code path setting errno */
+1:      b       safe_syscall_set_errno_tail
+        nop     /* per abi, for the linker to modify */
+
+        .cfi_endproc
+
+#if _CALL_ELF == 2
+        .size   safe_syscall_base, .-safe_syscall_base
+#else
+        .size   safe_syscall_base, .-.L.safe_syscall_base
+        .size   .L.safe_syscall_base, .-.L.safe_syscall_base
+#endif