@@ -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
new file mode 100644
@@ -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