@@ -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
new file mode 100644
@@ -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