sparc64: Add compile-time asserts for siginfo_t offsets

To help catch ABI breaks at compile-time, add compile-time assertions to
verify the siginfo_t layout. Unlike other architectures, sparc64 is
special, because it is one of few architectures requiring si_trapno.
ABI breaks around that field would only be caught here.

Link: https://lkml.kernel.org/r/m11rat9f85.fsf@fess.ebiederm.org
Link: https://lkml.kernel.org/r/20210429190734.624918-1-elver@google.com
Link: https://lkml.kernel.org/r/20210505141101.11519-1-ebiederm@xmission.com
Link: https://lkml.kernel.org/r/874kcvzbuu.fsf_-_@disp2133Suggested-by: Eric W. Biederman <ebiederm@xmission.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

arch/sparc/kernel/signal32.c

@@ -745,3 +745,38 @@ asmlinkage int do_sys32_sigstack(u32 u_ssptr, u32 u_ossptr, unsigned long sp)
 out:
 	return ret;
 }
+
+/*
+ * Compile-time assertions for siginfo_t offsets. Check NSIG* as well, as
+ * changes likely come with new fields that should be added below.
+ */
+static_assert(NSIGILL	== 11);
+static_assert(NSIGFPE	== 15);
+static_assert(NSIGSEGV	== 9);
+static_assert(NSIGBUS	== 5);
+static_assert(NSIGTRAP	== 6);
+static_assert(NSIGCHLD	== 6);
+static_assert(NSIGSYS	== 2);
+static_assert(offsetof(compat_siginfo_t, si_signo)	== 0x00);
+static_assert(offsetof(compat_siginfo_t, si_errno)	== 0x04);
+static_assert(offsetof(compat_siginfo_t, si_code)	== 0x08);
+static_assert(offsetof(compat_siginfo_t, si_pid)	== 0x0c);
+static_assert(offsetof(compat_siginfo_t, si_uid)	== 0x10);
+static_assert(offsetof(compat_siginfo_t, si_tid)	== 0x0c);
+static_assert(offsetof(compat_siginfo_t, si_overrun)	== 0x10);
+static_assert(offsetof(compat_siginfo_t, si_status)	== 0x14);
+static_assert(offsetof(compat_siginfo_t, si_utime)	== 0x18);
+static_assert(offsetof(compat_siginfo_t, si_stime)	== 0x1c);
+static_assert(offsetof(compat_siginfo_t, si_value)	== 0x14);
+static_assert(offsetof(compat_siginfo_t, si_int)	== 0x14);
+static_assert(offsetof(compat_siginfo_t, si_ptr)	== 0x14);
+static_assert(offsetof(compat_siginfo_t, si_addr)	== 0x0c);
+static_assert(offsetof(compat_siginfo_t, si_trapno)	== 0x10);
+static_assert(offsetof(compat_siginfo_t, si_addr_lsb)	== 0x10);
+static_assert(offsetof(compat_siginfo_t, si_lower)	== 0x14);
+static_assert(offsetof(compat_siginfo_t, si_upper)	== 0x18);
+static_assert(offsetof(compat_siginfo_t, si_pkey)	== 0x14);
+static_assert(offsetof(compat_siginfo_t, si_perf_data)	== 0x10);
+static_assert(offsetof(compat_siginfo_t, si_perf_type)	== 0x14);
+static_assert(offsetof(compat_siginfo_t, si_band)	== 0x0c);
+static_assert(offsetof(compat_siginfo_t, si_fd)		== 0x10);

arch/sparc/kernel/signal_64.c

@@ -556,3 +556,37 @@ void do_notify_resume(struct pt_regs *regs, unsigned long orig_i0, unsigned long
 	user_enter();
 }
 
+/*
+ * Compile-time assertions for siginfo_t offsets. Check NSIG* as well, as
+ * changes likely come with new fields that should be added below.
+ */
+static_assert(NSIGILL	== 11);
+static_assert(NSIGFPE	== 15);
+static_assert(NSIGSEGV	== 9);
+static_assert(NSIGBUS	== 5);
+static_assert(NSIGTRAP	== 6);
+static_assert(NSIGCHLD	== 6);
+static_assert(NSIGSYS	== 2);
+static_assert(offsetof(siginfo_t, si_signo)	== 0x00);
+static_assert(offsetof(siginfo_t, si_errno)	== 0x04);
+static_assert(offsetof(siginfo_t, si_code)	== 0x08);
+static_assert(offsetof(siginfo_t, si_pid)	== 0x10);
+static_assert(offsetof(siginfo_t, si_uid)	== 0x14);
+static_assert(offsetof(siginfo_t, si_tid)	== 0x10);
+static_assert(offsetof(siginfo_t, si_overrun)	== 0x14);
+static_assert(offsetof(siginfo_t, si_status)	== 0x18);
+static_assert(offsetof(siginfo_t, si_utime)	== 0x20);
+static_assert(offsetof(siginfo_t, si_stime)	== 0x28);
+static_assert(offsetof(siginfo_t, si_value)	== 0x18);
+static_assert(offsetof(siginfo_t, si_int)	== 0x18);
+static_assert(offsetof(siginfo_t, si_ptr)	== 0x18);
+static_assert(offsetof(siginfo_t, si_addr)	== 0x10);
+static_assert(offsetof(siginfo_t, si_trapno)	== 0x18);
+static_assert(offsetof(siginfo_t, si_addr_lsb)	== 0x18);
+static_assert(offsetof(siginfo_t, si_lower)	== 0x20);
+static_assert(offsetof(siginfo_t, si_upper)	== 0x28);
+static_assert(offsetof(siginfo_t, si_pkey)	== 0x20);
+static_assert(offsetof(siginfo_t, si_perf_data)	== 0x18);
+static_assert(offsetof(siginfo_t, si_perf_type)	== 0x20);
+static_assert(offsetof(siginfo_t, si_band)	== 0x10);
+static_assert(offsetof(siginfo_t, si_fd)	== 0x14);