cmd/cgo, runtime/cgo: avoid GCC/clang conversion warnings

Add explicit conversions to avoid warnings from -Wsign-conversion and
-Wshorten-64-to-32. Also avoid runtime errors from -fsanitize=undefined.

Fixes #48121

Change-Id: I29dc8d976884fc42826392c10f1e1759bb1a3989
Reviewed-on: https://go-review.googlesource.com/c/go/+/348739
Trust: Ian Lance Taylor <[email protected]>
Run-TryBot: Ian Lance Taylor <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>

Author: ianlancetaylor

src/cmd/cgo/out.go

@@ -1458,10 +1458,10 @@ const gccProlog = `
   (have a negative array count) and an inscrutable error will come
   out of the compiler and hopefully mention "name".
 */
-#define __cgo_compile_assert_eq(x, y, name) typedef char name[(x-y)*(x-y)*-2+1];
+#define __cgo_compile_assert_eq(x, y, name) typedef char name[(x-y)*(x-y)*-2UL+1UL];
 
 /* Check at compile time that the sizes we use match our expectations. */
-#define __cgo_size_assert(t, n) __cgo_compile_assert_eq(sizeof(t), n, _cgo_sizeof_##t##_is_not_##n)
+#define __cgo_size_assert(t, n) __cgo_compile_assert_eq(sizeof(t), (size_t)n, _cgo_sizeof_##t##_is_not_##n)
 
 __cgo_size_assert(char, 1)
 __cgo_size_assert(short, 2)

src/runtime/cgo/gcc_sigaction.c

@@ -49,13 +49,13 @@ x_cgo_sigaction(intptr_t signum, const go_sigaction_t *goact, go_sigaction_t *ol
 		sigemptyset(&act.sa_mask);
 		for (i = 0; i < 8 * sizeof(goact->mask); i++) {
 			if (goact->mask & ((uint64_t)(1)<<i)) {
-				sigaddset(&act.sa_mask, i+1);
+				sigaddset(&act.sa_mask, (int)(i+1));
 			}
 		}
-		act.sa_flags = goact->flags & ~SA_RESTORER;
+		act.sa_flags = (int)(goact->flags & ~(uint64_t)SA_RESTORER);
 	}
 
-	ret = sigaction(signum, goact ? &act : NULL, oldgoact ? &oldact : NULL);
+	ret = sigaction((int)signum, goact ? &act : NULL, oldgoact ? &oldact : NULL);
 	if (ret == -1) {
 		// runtime.rt_sigaction expects _cgo_sigaction to return errno on error.
 		_cgo_tsan_release();
@@ -70,11 +70,11 @@ x_cgo_sigaction(intptr_t signum, const go_sigaction_t *goact, go_sigaction_t *ol
 		}
 		oldgoact->mask = 0;
 		for (i = 0; i < 8 * sizeof(oldgoact->mask); i++) {
-			if (sigismember(&oldact.sa_mask, i+1) == 1) {
+			if (sigismember(&oldact.sa_mask, (int)(i+1)) == 1) {
 				oldgoact->mask |= (uint64_t)(1)<<i;
 			}
 		}
-		oldgoact->flags = oldact.sa_flags;
+		oldgoact->flags = (uint64_t)oldact.sa_flags;
 	}
 
 	_cgo_tsan_release();