[PATCH v4 5/9] common-user/host/mips: Add safe-syscall.inc.S

[Richard Henderson <richard.henderson@linaro.org>]

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 common-user/host/mips/hostdep.h          |   2 +
 common-user/host/mips/safe-syscall.inc.S | 135 +++++++++++++++++++++++
 2 files changed, 137 insertions(+)
 create mode 100644 common-user/host/mips/hostdep.h
 create mode 100644 common-user/host/mips/safe-syscall.inc.S

diff --git a/common-user/host/mips/hostdep.h b/common-user/host/mips/hostdep.h
new file mode 100644
index 0000000000..b18aca1deb
--- /dev/null
+++ b/common-user/host/mips/hostdep.h
@@ -0,0 +1,2 @@
+/* We have a safe-syscall.inc.S */
+#define HAVE_SAFE_SYSCALL
diff --git a/common-user/host/mips/safe-syscall.inc.S b/common-user/host/mips/safe-syscall.inc.S
new file mode 100644
index 0000000000..1e2f5a079c
--- /dev/null
+++ b/common-user/host/mips/safe-syscall.inc.S
@@ -0,0 +1,135 @@
+/*
+ * 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 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.
+ */
+
+#include "sys/regdef.h"
+#include "sys/asm.h"
+
+	.text
+	.set	nomips16
+	.set	noreorder
+
+	.global safe_syscall_start
+	.global safe_syscall_end
+	.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').
+	 */
+
+#if _MIPS_SIM == _ABIO32
+/* Do not allocate a stack frame and store into the parameter space. */
+#define FRAME   0
+#define ERRNOP  4
+#else
+/* Allocate a stack frame and store into the first allocated slot. */
+#define FRAME   16
+#define ERRNOP  0
+#endif
+
+NESTED(safe_syscall_base, FRAME, ra)
+	.cfi_startproc
+#if _MIPS_SIM == _ABIO32
+	/*
+	 * The syscall calling convention is nearly the same as C:
+	 * we enter with a0 == &signal_pending
+	 *               a1 == &errno
+	 *               a2 == syscall number
+	 *               a3, stack == syscall arguments
+	 *               and return the result in a0
+	 * and the syscall instruction needs
+	 *               v0 == syscall number
+	 *               a0 ... a3, stack == syscall arguments
+	 *               and returns the result in v0
+	 * Shuffle everything around appropriately.
+	 */
+	move	t0, a0		/* signal_pending pointer */
+	sw	a1, ERRNOP(sp)	/* errno pointer */
+	move	v0, a2		/* syscall number */
+	move	a0, a3		/* syscall arguments */
+	lw	a1, 16(sp)
+	lw	a2, 20(sp)
+	lw	a3, 24(sp)
+	lw	t4, 28(sp)
+	lw	t5, 32(sp)
+	lw	t6, 40(sp)
+	lw	t7, 44(sp)
+	sw	t4, 16(sp)
+	sw	t5, 20(sp)
+	sw	t6, 24(sp)
+	sw	t7, 28(sp)
+#else
+	PTR_ADDIU sp, sp, -FRAME
+	.cfi_adjust_cfa_offset FRAME
+
+	/*
+	 * The syscall calling convention is nearly the same as C:
+	 * we enter with a0 == &signal_pending
+	 *               a1 == &errno
+	 *               a2 == syscall number
+	 *               a3 ... a7, stack == syscall arguments
+	 *               and return the result in a0
+	 * and the syscall instruction needs
+	 *               v0 == syscall number
+	 *               a0 ... a5 == syscall arguments
+	 *               and returns the result in v0
+	 * Shuffle everything around appropriately.
+	 */
+	move	t0, a0		/* signal_pending pointer */
+	PTR_S	a1, ERRNOP(sp)	/* save errno pointer */
+	move	v0, a2		/* syscall number */
+	move	a0, a3		/* syscall arguments */
+	move	a1, a4
+	move	a2, a5
+	move	a3, a6
+	move	a4, a7
+	ld	a5, 16(sp)
+#endif
+
+	/*
+	 * 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 */
+	lw	t1, 0(t0)
+	bnez	t1, 0f
+	 nop
+	syscall
+safe_syscall_end:
+
+	/* code path for having successfully executed the syscall */
+	bnez	a3, 1f
+	 nop
+	jr	ra
+	 PTR_ADDIU sp, sp, FRAME
+
+	/* code path when we didn't execute the syscall */
+0:	li	v0, TARGET_ERESTARTSYS
+
+	/* code path setting errno */
+1:	PTR_L	t0, ERRNOP(sp)
+	sw	v0, 0(t0)		/* store errno */
+	li	v0, -1
+	jr	ra
+	 PTR_ADDIU sp, sp, FRAME
+
+	.cfi_endproc
+END(safe_syscall_base)
-- 
2.25.1