@@ -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.arm_pc;
+
+ 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
+
+ .cfi_sections .debug_frame
+
+ .text
+ .syntax unified
+ .arm
+ .align 2
+
+ /* 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:
+ .fnstart
+ .cfi_startproc
+ mov r12, sp /* save entry stack */
+ push { r4, r5, r6, r7, r8, lr }
+ .save { r4, r5, r6, r7, r8, lr }
+ .cfi_adjust_cfa_offset 24
+ .cfi_rel_offset r4, 0
+ .cfi_rel_offset r5, 4
+ .cfi_rel_offset r6, 8
+ .cfi_rel_offset r7, 12
+ .cfi_rel_offset r8, 16
+ .cfi_rel_offset lr, 20
+
+ /* The syscall calling convention isn't the same as the C one:
+ * we enter with r0 == *signal_pending
+ * r1 == syscall number
+ * r2, r3, [sp+0] ... [sp+12] == syscall arguments
+ * and return the result in r0
+ * and the syscall instruction needs
+ * r7 == syscall number
+ * r0 ... r6 == syscall arguments
+ * and returns the result in r0
+ * Shuffle everything around appropriately.
+ * Note the 16 bytes that we pushed to save registers.
+ */
+ mov r8, r0 /* copy signal_pending */
+ mov r7, r1 /* syscall number */
+ mov r0, r2 /* syscall args */
+ mov r1, r3
+ ldm r12, { r2, r3, r4, r5, r6 }
+
+ /* 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 */
+ ldr r12, [r8] /* signal_pending */
+ tst r12, r12
+ bne 1f
+ swi 0
+safe_syscall_end:
+ /* code path for having successfully executed the syscall */
+ pop { r4, r5, r6, r7, r8, pc }
+
+1:
+ /* code path when we didn't execute the syscall */
+ ldr r0, =-TARGET_ERESTARTSYS
+ pop { r4, r5, r6, r7, r8, pc }
+ .fnend
+ .cfi_endproc
+
+ .size safe_syscall_base, .-safe_syscall_base