compiler, runtime: allow slice to array pointer conversion

Panic if the slice is too short.

For golang/go#395

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/338630

2 files changed, 9 insertions, 0 deletions

diff --git a/libgo/go/runtime/error.go b/libgo/go/runtime/error.go
index 80655342f13..a8c82bbf8e8 100644
--- a/libgo/go/runtime/error.go
+++ b/libgo/go/runtime/error.go
@@ -175,6 +175,7 @@ const (
 	boundsSlice3B    // s[?:x:y], 0 <= x <= y failed (but boundsSlice3A didn't happen)
 	boundsSlice3C    // s[x:y:?], 0 <= x <= y failed (but boundsSlice3A/B didn't happen)
 
+	boundsConvert // (*[x]T)(s), 0 <= x <= len(s) failed
 	// Note: in the above, len(s) and cap(s) are stored in y
 )
 
@@ -190,6 +191,7 @@ var boundsErrorFmts = [...]string{
 	boundsSlice3Acap: "slice bounds out of range [::%x] with capacity %y",
 	boundsSlice3B:    "slice bounds out of range [:%x:%y]",
 	boundsSlice3C:    "slice bounds out of range [%x:%y:]",
+	boundsConvert:    "cannot convert slice with length %y to pointer to array with length %x",
 }
 
 // boundsNegErrorFmts are overriding formats if x is negative. In this case there's no need to report y.
diff --git a/libgo/go/runtime/panic.go b/libgo/go/runtime/panic.go
index 11396b4123a..a4b9a83d776 100644
--- a/libgo/go/runtime/panic.go
+++ b/libgo/go/runtime/panic.go
@@ -38,6 +38,7 @@ import (
 //go:linkname goPanicSlice3BU
 //go:linkname goPanicSlice3C
 //go:linkname goPanicSlice3CU
+//go:linkname goPanicSliceConvert
 //go:linkname panicshift
 //go:linkname panicdivide
 //go:linkname panicmem
@@ -175,6 +176,12 @@ func goPanicSlice3CU(x uint, y int) {
 	panic(boundsError{x: int64(x), signed: false, y: y, code: boundsSlice3C})
 }
 
+// failures in the conversion (*[x]T)s, 0 <= x <= y, x == cap(s)
+func goPanicSliceConvert(x int, y int) {
+	panicCheck1(getcallerpc(), "slice length too short to convert to pointer to array")
+	panic(boundsError{x: int64(x), signed: true, y: y, code: boundsConvert})
+}
+
 var shiftError = error(errorString("negative shift amount"))
 
 func panicshift() {