linux-user/host/sparc64: Add safe-syscall.inc.S

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

linux-user/host/sparc64/hostdep.h

@@ -12,4 +12,7 @@
 #ifndef SPARC64_HOSTDEP_H
 #define SPARC64_HOSTDEP_H
 
+/* We have a safe-syscall.inc.S */
+#define HAVE_SAFE_SYSCALL
+
 #endif

linux-user/host/sparc64/safe-syscall.inc.S

+/*
+ * 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 linux-user/safe-syscall.S
+ *
+ * Written by Richard Henderson <richard.henderson@linaro.org>
+ * Copyright (C) 2021 Linaro, 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.
+ */
+
+        .text
+        .balign 4
+
+        .register %g2, #scratch
+        .register %g3, #scratch
+
+        .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
+
+#define STACK_BIAS  2047
+#define PARAM(N)    STACK_BIAS + N*8
+
+        /*
+         * 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 o0 == &signal_pending
+         *               o1 == syscall number
+         *               o2 ... o5, (stack) == syscall arguments
+         *               and return the result in x0
+         * and the syscall instruction needs
+         *               g1 == syscall number
+         *               o0 ... o5 == syscall arguments
+         *               and returns the result in o0
+         * Shuffle everything around appropriately.
+         */
+        mov     %o0, %g2                /* signal_pending pointer */
+        mov     %o1, %g1                /* syscall number */
+        mov     %o2, %o0                /* syscall arguments */
+        mov     %o3, %o1
+        mov     %o4, %o2
+        mov     %o5, %o3
+        ldx     [%sp + PARAM(6)], %o4
+        ldx     [%sp + PARAM(7)], %o5
+
+        /*
+         * 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 */
+        lduw    [%g2], %g3
+        brnz,pn %g3, 2f
+         nop
+        ta      0x6d
+safe_syscall_end:
+        /* code path for having successfully executed the syscall */
+        bcs,pn  %xcc, 1f
+         nop
+        ret
+         nop
+
+        /* code path when we didn't execute the syscall */
+2:      set     TARGET_ERESTARTSYS, %o0
+
+        /* code path setting errno */
+1:      mov     %o7, %g1
+        call    safe_syscall_set_errno_tail
+         mov    %g1, %o7
+
+        .cfi_endproc
+        .size   safe_syscall_base, .-safe_syscall_base