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authorPeter Maydell <peter.maydell@linaro.org>2016-06-13 13:34:56 +0100
committerPeter Maydell <peter.maydell@linaro.org>2016-06-13 17:27:23 +0100
commit51495272972424e3d388c9fcf2a75412ac883664 (patch)
tree900bd987a8ba8db9707f75ab28c7c2dbe0cba598
parenta9f979ba0a4d7db3062f78fc545d2400fcfce9d6 (diff)
downloadqemu-arm-51495272972424e3d388c9fcf2a75412ac883664.tar.gz
linux-user: Implement safe_syscall for 64-bit ARM
Implement the host assembly fragment needed for safe_syscall for 64-bit ARM. Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
-rw-r--r--linux-user/host/aarch64/hostdep.h23
-rw-r--r--linux-user/host/aarch64/safe-syscall.inc.S78
2 files changed, 101 insertions, 0 deletions
diff --git a/linux-user/host/aarch64/hostdep.h b/linux-user/host/aarch64/hostdep.h
index 7609bf5cd7..e2c28e6ea6 100644
--- a/linux-user/host/aarch64/hostdep.h
+++ b/linux-user/host/aarch64/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 long *pcreg = &uc->uc_mcontext.pc;
+
+ 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/aarch64/safe-syscall.inc.S b/linux-user/host/aarch64/safe-syscall.inc.S
new file mode 100644
index 0000000000..2c21489e66
--- /dev/null
+++ b/linux-user/host/aarch64/safe-syscall.inc.S
@@ -0,0 +1,78 @@
+/*
+ * 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 Peter Maydell <peter.maydell@linaro.org>
+ *
+ * Copyright (C) 2016 Linaro Limited
+ *
+ * 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
+ .align 4
+
+ /* 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
+
+ /* The syscall calling convention isn't the same as the
+ * C one:
+ * we enter with x0 == *signal_pending
+ * x1 == syscall number
+ * x2, x3, x4, x5, x6, x7 == syscall arguments
+ * and return the result in x0
+ * and the syscall instruction needs
+ * x8 == syscall number
+ * x0, x1, x2, x3, x4, x5 == syscall arguments
+ * and returns the result in r0
+ * Shuffle everything around appropriately.
+ */
+ mov x9, x0 /* signal-pending pointer */
+ mov x8, x1 /* syscall number */
+ /* and the syscall arguments */
+ mov x0, x2
+ mov x1, x3
+ mov x2, x4
+ mov x3, x5
+ mov x4, x6
+ mov x5, x7
+
+ /* 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 w10, [x9]
+ cmp w10, #0
+ b.ne return_ERESTARTSYS
+ svc 0x0
+safe_syscall_end:
+ /* code path for having successfully executed the syscall */
+ /* NB: we assume we're not trying to do old ARMv4T interworking */
+ ret
+
+return_ERESTARTSYS:
+ /* code path when we didn't execute the syscall */
+ mov x0, #-TARGET_ERESTARTSYS
+ ret
+ .cfi_endproc
+
+ .size safe_syscall_base, .-safe_syscall_base