[Qemu-devel] [PULL v2 24/24] linux-user: Provide safe_syscall for ppc64

[riku.voipio@linaro.org]

From: Richard Henderson <rth@twiddle.net>

Signed-off-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
---
 linux-user/host/ppc64/hostdep.h          | 23 ++++++++
 linux-user/host/ppc64/safe-syscall.inc.S | 92 ++++++++++++++++++++++++++++++++
 2 files changed, 115 insertions(+)
 create mode 100644 linux-user/host/ppc64/safe-syscall.inc.S

diff --git a/linux-user/host/ppc64/hostdep.h b/linux-user/host/ppc64/hostdep.h
index 7609bf5..310e7d1 100644
--- a/linux-user/host/ppc64/hostdep.h
+++ b/linux-user/host/ppc64/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.gp_regs[PT_NIP];
+
+    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/ppc64/safe-syscall.inc.S b/linux-user/host/ppc64/safe-syscall.inc.S
new file mode 100644
index 0000000..d30050a
--- /dev/null
+++ b/linux-user/host/ppc64/safe-syscall.inc.S
@@ -0,0 +1,92 @@
+/*
+ * 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
+
+	.text
+
+	/* 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.
+	 */
+#if _CALL_ELF == 2
+safe_syscall_base:
+	.cfi_startproc
+	.localentry safe_syscall_base,0
+#else
+	.section ".opd","aw"
+	.align	3
+safe_syscall_base:
+	.quad	.L.safe_syscall_base,.TOC.@tocbase,0
+	.previous
+.L.safe_syscall_base:
+	.cfi_startproc
+#endif
+	/* We enter with r3 == *signal_pending
+	 *               r4 == syscall number
+	 *               r5 ... r10 == syscall arguments
+	 *               and return the result in r3
+	 * and the syscall instruction needs
+	 *               r0 == syscall number
+	 *               r3 ... r8 == syscall arguments
+	 *               and returns the result in r3
+	 * Shuffle everything around appropriately.
+	 */
+	mr	11, 3	/* signal_pending */
+	mr	0, 4	/* syscall number */
+	mr	3, 5	/* syscall arguments */
+	mr	4, 6
+	mr	5, 7
+	mr	6, 8
+	mr	7, 9
+	mr	8, 10
+
+	/* 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 */
+	lwz	12, 0(11)
+	cmpwi	0, 12, 0
+	bne-	0f
+	sc
+safe_syscall_end:
+	/* code path when we did execute the syscall */
+	bnslr+
+
+	/* syscall failed; return negative errno */
+	neg	3, 3
+	blr
+
+	/* code path when we didn't execute the syscall */
+0:	addi	3, 0, -TARGET_ERESTARTSYS
+	blr
+	.cfi_endproc
+
+#if _CALL_ELF == 2
+	.size	safe_syscall_base, .-safe_syscall_base
+#else
+	.size	safe_syscall_base, .-.L.safe_syscall_base
+	.size	.L.safe_syscall_base, .-.L.safe_syscall_base
+#endif
-- 
2.1.4