[PATCH v4 6/9] common-user/host/sparc64: Add safe-syscall.inc.S

[Richard Henderson]

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 common-user/host/sparc64/hostdep.h          |  2 +
 common-user/host/sparc64/safe-syscall.inc.S | 91 +++++++++++++++++++++
 2 files changed, 93 insertions(+)
 create mode 100644 common-user/host/sparc64/hostdep.h
 create mode 100644 common-user/host/sparc64/safe-syscall.inc.S

diff --git a/common-user/host/sparc64/hostdep.h 
b/common-user/host/sparc64/hostdep.h
new file mode 100644
index 0000000000..b18aca1deb
--- /dev/null
+++ b/common-user/host/sparc64/hostdep.h
@@ -0,0 +1,2 @@
+/* We have a safe-syscall.inc.S */
+#define HAVE_SAFE_SYSCALL
diff --git a/common-user/host/sparc64/safe-syscall.inc.S 
b/common-user/host/sparc64/safe-syscall.inc.S
new file mode 100644
index 0000000000..2492fcbd9e
--- /dev/null
+++ b/common-user/host/sparc64/safe-syscall.inc.S
@@ -0,0 +1,91 @@
+/*
+ * 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 <rth@twiddle.net>
+ * Copyright (C) 2021 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.
+ */
+
+       .text
+       .balign 4
+
+       .global safe_syscall_base
+       .global safe_syscall_start
+       .global safe_syscall_end
+       .type   safe_syscall_base, @function
+       .type   safe_syscall_start, @object
+       .type   safe_syscall_end, @object
+
+#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 == errno
+        *               o2 == syscall number
+        *               o3 ... 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 */
+       stx     %o1, [%sp + PARAM(1)]   /* save errno pointer */
+       mov     %o2, %g1                /* syscall number */
+       mov     %o3, %o0                /* syscall arguments */
+       mov     %o4, %o1
+       mov     %o5, %o2
+       ldx     [%sp + PARAM(6)], %o3
+       ldx     [%sp + PARAM(7)], %o4
+       ldx     [%sp + PARAM(8)], %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 */
+       bcc,pt  %xcc, 9f
+        nop
+
+       /* code path setting errno */
+1:     ldx     [%sp + PARAM(1)], %g2
+       stw     %o0, [%g2]              /* store errno */
+       set     -1, %o0
+
+9:     ret
+        nop
+
+       /* code path when we didn't execute the syscall */
+2:     ba,pt   %xcc, 1b
+        set    TARGET_ERESTARTSYS, %o0
+
+       .cfi_endproc
+       .size   safe_syscall_base, .-safe_syscall_base
-- 
2.25.1