[RESEND PATCH v9 27/28] linux-user: Add safe syscall handling for loongarch64 hosts

[Song Gao <gaosong@loongson.cn>]

From: WANG Xuerui <git@xen0n.name>

Signed-off-by: WANG Xuerui <git@xen0n.name>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210925173032.2434906-29-git@xen0n.name>
Signed-off-by: Song Gao <gaosong@loongson.cn>
Signed-off-by: Xiaojuan Yang <yangxiaojuan@loongson.cn>
---
 linux-user/host/loongarch64/hostdep.h          | 32 +++++++++++
 linux-user/host/loongarch64/safe-syscall.inc.S | 78 ++++++++++++++++++++++++++
 2 files changed, 110 insertions(+)
 create mode 100644 linux-user/host/loongarch64/hostdep.h
 create mode 100644 linux-user/host/loongarch64/safe-syscall.inc.S

diff --git a/linux-user/host/loongarch64/hostdep.h b/linux-user/host/loongarch64/hostdep.h
new file mode 100644
index 0000000..e67ecad
--- /dev/null
+++ b/linux-user/host/loongarch64/hostdep.h
@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Things which are dependent on the host architecture
+ */
+
+#ifndef LOONGARCH64_HOSTDEP_H
+#define LOONGARCH64_HOSTDEP_H
+
+/* We have a safe-syscall.inc.S */
+#define HAVE_SAFE_SYSCALL
+
+#ifndef __ASSEMBLER__
+
+/* These are defined by the safe-syscall.inc.S file */
+extern char safe_syscall_start[];
+extern char safe_syscall_end[];
+
+/* Adjust the signal context to rewind out of safe-syscall if we're in it */
+static inline void rewind_if_in_safe_syscall(void *puc)
+{
+    ucontext_t *uc = puc;
+    unsigned long long *pcreg = &uc->uc_mcontext.__pc;
+
+    if (*pcreg > (uintptr_t)safe_syscall_start
+        && *pcreg < (uintptr_t)safe_syscall_end) {
+        *pcreg = (uintptr_t)safe_syscall_start;
+    }
+}
+
+#endif /* __ASSEMBLER__ */
+
+#endif
diff --git a/linux-user/host/loongarch64/safe-syscall.inc.S b/linux-user/host/loongarch64/safe-syscall.inc.S
new file mode 100644
index 0000000..6220dde
--- /dev/null
+++ b/linux-user/host/loongarch64/safe-syscall.inc.S
@@ -0,0 +1,78 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * 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
+ *
+ * Ported to LoongArch by WANG Xuerui <git@xen0n.name>
+ *
+ * Based on safe-syscall.inc.S code for every other architecture,
+ * originally written by Richard Henderson <rth@twiddle.net>
+ * Copyright (C) 2018 Linaro, Inc.
+ */
+
+	.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
+
+	/*
+	 * 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').
+	 * We return a long which is the syscall's return value, which
+	 * may be negative-errno on failure. Conversion to the
+	 * -1-and-errno-set convention is done by the calling wrapper.
+	 */
+safe_syscall_base:
+	.cfi_startproc
+	/*
+	 * The syscall calling convention is nearly the same as C:
+	 * we enter with a0 == *signal_pending
+	 *               a1 == syscall number
+	 *               a2 ... a7 == syscall arguments
+	 *               and return the result in a0
+	 * and the syscall instruction needs
+	 *               a7 == syscall number
+	 *               a0 ... a5 == syscall arguments
+	 *               and returns the result in a0
+	 * Shuffle everything around appropriately.
+	 */
+	move	$t0, $a0	/* signal_pending pointer */
+	move	$t1, $a1	/* syscall number */
+	move	$a0, $a2	/* syscall arguments */
+	move	$a1, $a3
+	move	$a2, $a4
+	move	$a3, $a5
+	move	$a4, $a6
+	move	$a5, $a7
+	move	$a7, $t1
+
+	/*
+	 * 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 */
+	ld.w	$t1, $t0, 0
+	bnez	$t1, 0f
+	syscall	0
+safe_syscall_end:
+	/* code path for having successfully executed the syscall */
+	jr	$ra
+
+0:
+	/* code path when we didn't execute the syscall */
+	li.w	$a0, -TARGET_ERESTARTSYS
+	jr	$ra
+	.cfi_endproc
+
+	.size	safe_syscall_base, .-safe_syscall_base
-- 
1.8.3.1