m68k: Verify the offsets in struct siginfo never change.

A change to the generic struct siginfo accidentally changed the offset
of si_offset.  Add build time checks to ensure the offsets of all known
fields in struct siginfo never change.  This copies the form of similar
changes on x86.
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

arch/m68k/kernel/signal.c

@@ -574,6 +574,66 @@ static inline int rt_save_fpu_state(struct ucontext __user *uc, struct pt_regs *
 
 #endif /* CONFIG_FPU */
 
+static inline void siginfo_build_tests(void)
+{
+	/* This needs to be tested on m68k as it has a lesser
+	 * alignment requirment than x86 and that can cause surprises.
+	 */
+
+	/* This is part of the ABI and can never change in size: */
+	BUILD_BUG_ON(sizeof(siginfo_t) != 128);
+
+	/* Ensure the know fields never change in location */
+	BUILD_BUG_ON(offsetof(siginfo_t, si_signo) != 0);
+	BUILD_BUG_ON(offsetof(siginfo_t, si_errno) != 4);
+	BUILD_BUG_ON(offsetof(siginfo_t, si_code)  != 8);
+
+	/* _kill */
+	BUILD_BUG_ON(offsetof(siginfo_t, si_pid) != 0x0C);
+	BUILD_BUG_ON(offsetof(siginfo_t, si_uid) != 0x10);
+
+	/* _timer */
+	BUILD_BUG_ON(offsetof(siginfo_t, si_tid)     != 0x0C);
+	BUILD_BUG_ON(offsetof(siginfo_t, si_overrun) != 0x10);
+	BUILD_BUG_ON(offsetof(siginfo_t, si_value)   != 0x14);
+
+	/* _rt */
+	BUILD_BUG_ON(offsetof(siginfo_t, si_pid)   != 0x0C);
+	BUILD_BUG_ON(offsetof(siginfo_t, si_uid)   != 0x10);
+	BUILD_BUG_ON(offsetof(siginfo_t, si_value) != 0x14);
+
+	/* _sigchld */
+	BUILD_BUG_ON(offsetof(siginfo_t, si_pid)    != 0x0C);
+	BUILD_BUG_ON(offsetof(siginfo_t, si_uid)    != 0x10);
+	BUILD_BUG_ON(offsetof(siginfo_t, si_status) != 0x14);
+	BUILD_BUG_ON(offsetof(siginfo_t, si_utime)  != 0x18);
+	BUILD_BUG_ON(offsetof(siginfo_t, si_stime)  != 0x1C);
+
+	/* _sigfault */
+	BUILD_BUG_ON(offsetof(siginfo_t, si_addr) != 0x0C);
+
+	/* _sigfault._mcerr */
+	BUILD_BUG_ON(offsetof(siginfo_t, si_addr_lsb) != 0x10);
+
+	/* _sigfault._addr_bnd */
+	BUILD_BUG_ON(offsetof(siginfo_t, si_lower) != 0x12);
+	BUILD_BUG_ON(offsetof(siginfo_t, si_upper) != 0x16);
+
+	/* _sigfault._addr_pkey */
+	BUILD_BUG_ON(offsetof(siginfo_t, si_pkey) != 0x12);
+
+	/* _sigpoll */
+	BUILD_BUG_ON(offsetof(siginfo_t, si_band)   != 0x0C);
+	BUILD_BUG_ON(offsetof(siginfo_t, si_fd)     != 0x10);
+
+	/* _sigsys */
+	BUILD_BUG_ON(offsetof(siginfo_t, si_call_addr) != 0x0C);
+	BUILD_BUG_ON(offsetof(siginfo_t, si_syscall)   != 0x10);
+	BUILD_BUG_ON(offsetof(siginfo_t, si_arch)      != 0x14);
+
+	/* any new si_fields should be added here */
+}
+
 static int mangle_kernel_stack(struct pt_regs *regs, int formatvec,
 			       void __user *fp)
 {
@@ -635,6 +695,8 @@ restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *usc, void __u
 	struct sigcontext context;
 	int err = 0;
 
+	siginfo_build_tests();
+
 	/* Always make any pending restarted system calls return -EINTR */
 	current->restart_block.fn = do_no_restart_syscall;