runtime: add padding to Linux kernel structures

Go exchanges siginfo and sigevent structures with the kernel. They
contain unions, but Go's use is limited to the first few fields. Pad out
the rest so the size Go sees is the same as what the Linux kernel sees.

This is a follow-up to CL 342052 which added the sigevent struct without
padding. It updates the siginfo struct as well so there are no bad
examples in the defs_linux_*.go files.

Change-Id: Id991d4a57826677dd7e6cc30ad113fa3b321cddf
Reviewed-on: https://go-review.googlesource.com/c/go/+/353136
Run-TryBot: Rhys Hiltner <rhys@justin.tv>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
Trust: Michael Knyszek <mknyszek@google.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/src/runtime/os_linux.go b/src/runtime/os_linux.go
index 06773c2193..d5a5ff763b 100644
--- a/src/runtime/os_linux.go
+++ b/src/runtime/os_linux.go
@@ -440,6 +440,18 @@ func pipe() (r, w int32, errno int32)
 func pipe2(flags int32) (r, w int32, errno int32)
 func setNonblock(fd int32)
 
+const (
+	_si_max_size    = 128
+	_sigev_max_size = 64
+)
+
+// Assert that the Go definitions of structures exchanged with the kernel are
+// the same size as what the kernel defines.
+var (
+	_ [_si_max_size]struct{}    = [unsafe.Sizeof(siginfo{})]struct{}{}
+	_ [_sigev_max_size]struct{} = [unsafe.Sizeof(sigevent{})]struct{}{}
+)
+
 //go:nosplit
 //go:nowritebarrierrec
 func setsig(i uint32, fn uintptr) {