linux-user: Renumber TARGET_QEMU_ESIGRETURN, make it not arch-specific

Currently we define a QEMU-internal errno TARGET_QEMU_ESIGRETURN
only on the MIPS and PPC targets; move this to errno_defs.h
so it is available for all architectures, and renumber it to 513.
We pick 513 because this is safe from future use as a system call return
value: Linux uses it as ERESTART_NOINTR internally and never allows that
errno to escape to userspace.
Signed-off-by: NTimothy Edward Baldwin <T.E.Baldwin99@members.leeds.ac.uk>
Message-id: 1441497448-32489-4-git-send-email-T.E.Baldwin99@members.leeds.ac.uk
[PMM: TARGET_ERESTARTSYS split out into preceding patch, add comment]
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NLaurent Vivier <laurent@vivier.eu>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NRiku Voipio <riku.voipio@linaro.org>

linux-user/errno_defs.h

@@ -147,3 +147,12 @@
  * kernel uses for the same purpose.
  */
 #define TARGET_ERESTARTSYS     512     /* Restart system call (if SA_RESTART) */
+
+/* QEMU internal, not visible to the guest. This is returned by the
+ * do_sigreturn() code after a successful sigreturn syscall, to indicate
+ * that it has correctly set the guest registers and so the main loop
+ * should not touch them. We use the value the guest would use for
+ * ERESTART_NOINTR (which is kernel internal) to guarantee that we won't
+ * clash with a valid guest errno now or in the future.
+ */
+#define TARGET_QEMU_ESIGRETURN 513     /* Return from signal */

linux-user/mips/target_syscall.h

@@ -222,10 +222,6 @@ struct target_pt_regs {
 #define TARGET_ENOTRECOVERABLE 166     /* State not recoverable */
 
 
-
-/* Nasty hack: define a fake errno value for use by sigreturn.  */
-#define TARGET_QEMU_ESIGRETURN 255
-
 #define UNAME_MACHINE "mips"
 #define UNAME_MINIMUM_RELEASE "2.6.32"
 

linux-user/mips64/target_syscall.h

@@ -219,10 +219,6 @@ struct target_pt_regs {
 #define TARGET_ENOTRECOVERABLE 166     /* State not recoverable */
 
 
-
-/* Nasty hack: define a fake errno value for use by sigreturn. */
-#define TARGET_QEMU_ESIGRETURN 255
-
 #define UNAME_MACHINE "mips64"
 #define UNAME_MINIMUM_RELEASE "2.6.32"
 

linux-user/ppc/target_syscall.h

@@ -53,8 +53,6 @@ struct target_revectored_struct {
 	abi_ulong __map[8];			/* 256 bits */
 };
 
-/* Nasty hack: define a fake errno value for use by sigreturn.  */
-#define TARGET_QEMU_ESIGRETURN 255
 
 /*
  * flags masks