[Qemu-devel] [PATCH v2 4/5] linux-user: Provide safe_syscall for s390x

[Richard Henderson <rth@twiddle.net>]

Signed-off-by: Richard Henderson <rth@twiddle.net>
---
 linux-user/host/s390x/hostdep.h          | 23 ++++++++
 linux-user/host/s390x/safe-syscall.inc.S | 90 ++++++++++++++++++++++++++++++++
 2 files changed, 113 insertions(+)
 create mode 100644 linux-user/host/s390x/safe-syscall.inc.S

diff --git a/linux-user/host/s390x/hostdep.h b/linux-user/host/s390x/hostdep.h
index 7609bf5..e95871c 100644
--- a/linux-user/host/s390x/hostdep.h
+++ b/linux-user/host/s390x/hostdep.h
@@ -12,4 +12,27 @@
 #ifndef QEMU_HOSTDEP_H
 #define QEMU_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)
+{
+    struct ucontext *uc = puc;
+    unsigned long *pcreg = &uc->uc_mcontext.psw.addr;
+
+    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/s390x/safe-syscall.inc.S b/linux-user/host/s390x/safe-syscall.inc.S
new file mode 100644
index 0000000..f1b446a
--- /dev/null
+++ b/linux-user/host/s390x/safe-syscall.inc.S
@@ -0,0 +1,90 @@
+/*
+ * 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) 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').
+	 * 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
+	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 */
+	lt	%r0,0(%r8)
+	jne	2f
+	svc	0
+safe_syscall_end:
+
+1:	lg	%r15,0(%r15)		/* load back chain */
+	.cfi_remember_state
+	.cfi_adjust_cfa_offset -160
+	lmg	%r6,%r15,48(%r15)	/* load saved registers */
+	br	%r14
+	.cfi_restore_state
+2:	lghi	%r2, -TARGET_ERESTARTSYS
+	j	1b
+	.cfi_endproc
+
+	.size	safe_syscall_base, .-safe_syscall_base
-- 
2.5.5