cmd/gc: in the runtime package, don't promote any decls to the heap.

In the runtime, we want to control where allocations happen.
In particular, we don't want the code implementing malloc to
itself trigger a malloc.  This change prevents the compiler
from inserting mallocs on our behalf (due to escaping declarations).

This check does not trigger on the current runtime code.

Note: Composite literals are still allowed.

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/105280047

diff --git a/src/cmd/gc/gen.c b/src/cmd/gc/gen.c
index cf630f34843186ad834dcb390b738b9039e34afb..908a5e53d980627c793e469807b483a674a27206 100644 (file)
--- a/src/cmd/gc/gen.c
+++ b/src/cmd/gc/gen.c
@@ -584,6 +584,8 @@ cgen_dcl(Node *n)
        }
        if(!(n->class & PHEAP))
                return;
+       if(compiling_runtime)
+               fatal("%N escapes to heap, not allowed in runtime.", n);
        if(n->alloc == nil)
                n->alloc = callnew(n->type);
        cgen_as(n->heapaddr, n->alloc);