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>

1 files changed, 98 insertions, 0 deletions

diff --git a/common-user/host/s390x/safe-syscall.inc.S b/common-user/host/s390x/safe-syscall.inc.S
new file mode 100644
index 0000000000..2ccbaa2402
--- /dev/null
+++ b/common-user/host/s390x/safe-syscall.inc.S
@@ -0,0 +1,98 @@
+/*
+ * 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
+
+        /* 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
+        stmg    %r6,%r15,48(%r15)       /* save all call-saved registers */
+        .cfi_offset %r15,-40
+        .cfi_offset %r14,-48
+        .cfi_offset %r13,-56
+        .cfi_offset %r12,-64
+        .cfi_offset %r11,-72
+        .cfi_offset %r10,-80
+        .cfi_offset %r9,-88
+        .cfi_offset %r8,-96
+        .cfi_offset %r7,-104
+        .cfi_offset %r6,-112
+        lgr     %r1,%r15
+        lg      %r0,8(%r15)             /* load eos */
+        aghi    %r15,-160
+        .cfi_adjust_cfa_offset 160
+        stg     %r1,0(%r15)             /* store back chain */
+        stg     %r0,8(%r15)             /* store eos */
+
+        /*
+         * The syscall calling convention isn't the same as the C one:
+         * we enter with r2 == &signal_pending
+         *               r3 == syscall number
+         *               r4, r5, r6, (stack) == syscall arguments
+         *               and return the result in r2
+         * and the syscall instruction needs
+         *               r1 == syscall number
+         *               r2 ... r7 == syscall arguments
+         *               and returns the result in r2
+         * Shuffle everything around appropriately.
+         */
+        lgr     %r8,%r2                 /* signal_pending pointer */
+        lgr     %r1,%r3                 /* syscall number */
+        lgr     %r2,%r4                 /* syscall args */
+        lgr     %r3,%r5
+        lgr     %r4,%r6
+        lmg     %r5,%r7,320(%r15)
+
+        /* 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 */
+        icm     %r0,15,0(%r8)
+        jne     2f
+        svc     0
+safe_syscall_end:
+
+        /* code path for having successfully executed the syscall */
+        lg      %r15,0(%r15)            /* load back chain */
+        .cfi_remember_state
+        .cfi_adjust_cfa_offset -160
+        lmg     %r6,%r15,48(%r15)       /* load saved registers */
+
+        lghi    %r0, -4095              /* check for syscall error */
+        clgr    %r2, %r0
+        blr     %r14                    /* return on success */
+        lcr     %r2, %r2                /* create positive errno */
+        jg      safe_syscall_set_errno_tail
+        .cfi_restore_state
+
+        /* code path when we didn't execute the syscall */
+2:      lg      %r15,0(%r15)            /* load back chain */
+        .cfi_adjust_cfa_offset -160
+        lmg     %r6,%r15,48(%r15)       /* load saved registers */
+        lghi    %r2, QEMU_ERESTARTSYS
+        jg      safe_syscall_set_errno_tail
+
+        .cfi_endproc
+        .size   safe_syscall_base, .-safe_syscall_base