runtime: delete panicstring; move its checks into gopanic

In Go 1.3 the runtime called panicstring to report errors like
divide by zero or memory faults. Now we call panic (gopanic)
with pre-allocated error values. That new path is missing the
checking that panicstring did, so add it there.

The only call to panicstring left is in cnew, which is problematic
because if it fails, probably the heap is corrupt. In that case,
calling panicstring creates a new errorCString (no allocation there),
but then panic tries to print it, invoking errorCString.Error, which
does a string concatenation (allocating), which then dies.
Replace that one panicstring with a throw: cnew is for allocating
runtime data structures and should never ask for an inappropriate
amount of memory.

With panicstring gone, delete newErrorCString, errorCString.
While we're here, delete newErrorString, not called by anyone.
(It can't be: that would be C code calling Go code that might
block or grow the stack.)

Found while debugging a malloc corruption.
This resulted in 'panic during panic' instead of a more useful message.

LGTM=khr
R=khr
CC=golang-codereviews
https://golang.org/cl/138290045

1 files changed, 0 insertions, 22 deletions

diff --git a/src/runtime/error.go b/src/runtime/error.go
index 3ea93680ce..0b40c702b0 100644
--- a/src/runtime/error.go
+++ b/src/runtime/error.go
@@ -71,28 +71,6 @@ func (e errorString) Error() string {
 	return "runtime error: " + string(e)
 }
 
-// For calling from C.
-func newErrorString(s string, ret *interface{}) {
-	*ret = errorString(s)
-}
-
-// An errorCString represents a runtime error described by a single C string.
-// Not "type errorCString unsafe.Pointer" because of http://golang.org/issue/7084.
-// Not uintptr because we want to avoid an allocation if interfaces can't hold
-// uintptrs directly (and cstr _is_ a pointer).
-type errorCString struct{ cstr unsafe.Pointer }
-
-func (e errorCString) RuntimeError() {}
-
-func (e errorCString) Error() string {
-	return "runtime error: " + gostringnocopy((*byte)(e.cstr))
-}
-
-// For calling from C.
-func newErrorCString(s unsafe.Pointer, ret *interface{}) {
-	*ret = errorCString{s}
-}
-
 type stringer interface {
 	String() string
 }