compiler, runtime: check len/cap for append(s, make(T, l)...)

The overflow checks done in growslice always reported an error for the
capacity argument, even if it was the length argument that overflowed.
This change lets the code pass the current issue4085b.go test.

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/273806

1 files changed, 9 insertions, 2 deletions

diff --git a/libgo/go/runtime/slice.go b/libgo/go/runtime/slice.go
index 97b26594dad..ddd588ed5b9 100644
--- a/libgo/go/runtime/slice.go
+++ b/libgo/go/runtime/slice.go
@@ -15,6 +15,7 @@ import (
 //go:linkname panicmakeslicelen
 //go:linkname panicmakeslicecap
 //go:linkname makeslice
+//go:linkname checkMakeSlice
 //go:linkname makeslice64
 //go:linkname growslice
 //go:linkname slicecopy
@@ -91,6 +92,13 @@ func makeslicecopy(et *_type, tolen int, fromlen int, from unsafe.Pointer) unsaf
 }
 
 func makeslice(et *_type, len, cap int) unsafe.Pointer {
+	mem := checkMakeSlice(et, len, cap)
+	return mallocgc(mem, et, true)
+}
+
+// checkMakeSlice is called for append(s, make([]T, len, cap)...) to check
+// the values of len and cap.
+func checkMakeSlice(et *_type, len, cap int) uintptr {
 	mem, overflow := math.MulUintptr(et.size, uintptr(cap))
 	if overflow || mem > maxAlloc || len < 0 || len > cap {
 		// NOTE: Produce a 'len out of range' error instead of a
@@ -104,8 +112,7 @@ func makeslice(et *_type, len, cap int) unsafe.Pointer {
 		}
 		panicmakeslicecap()
 	}
-
-	return mallocgc(mem, et, true)
+	return mem
 }
 
 func makeslice64(et *_type, len64, cap64 int64) unsafe.Pointer {