runtime: efence support for growable stacks

1. Fix the bug that shrinkstack returns memory to heap.
   This causes growslice to misbehave (it manually initialized
   blocks, and in efence mode shrinkstack's free leads to
   partially-initialized blocks coming out of growslice.
   Which in turn causes GC to crash while treating the garbage
   as Eface/Iface.
2. Enable efence for stack segments.

LGTM=rsc
R=golang-codereviews, rsc
CC=golang-codereviews, khr
https://golang.org/cl/74080043

diff --git a/src/pkg/runtime/stack.c b/src/pkg/runtime/stack.c
index 4d699f1101ac0c68f1686228344f58f4bf3d511e..4bdc24107c82543e943f00ae9913b1a878596e5d 100644 (file)
--- a/src/pkg/runtime/stack.c
+++ b/src/pkg/runtime/stack.c
@@ -102,7 +102,7 @@ runtime·stackalloc(G *gp, uint32 n)
                runtime·printf("stackalloc %d\n", n);
 
        gp->stacksize += n;
-       if(StackFromSystem)
+       if(runtime·debug.efence || StackFromSystem)
                return runtime·SysAlloc(ROUND(n, PageSize), &mstats.stacks_sys);
 
        // Minimum-sized stacks are allocated with a fixed-size free-list allocator,
@@ -143,8 +143,8 @@ runtime·stackfree(G *gp, void *v, Stktop *top)
        if(StackDebug >= 1)
                runtime·printf("stackfree %p %d\n", v, (int32)n);
        gp->stacksize -= n;
-       if(StackFromSystem) {
-               if(StackFaultOnFree)
+       if(runtime·debug.efence || StackFromSystem) {
+               if(runtime·debug.efence || StackFaultOnFree)
                        runtime·SysFault(v, n);
                else
                        runtime·SysFree(v, n, &mstats.stacks_sys);
@@ -819,7 +819,15 @@ runtime·shrinkstack(G *gp)
                gp->stack0 = (uintptr)oldstk + newsize;
        gp->stacksize -= oldsize - newsize;
 
-       // Free bottom half of the stack.  First, we trick malloc into thinking
+       // Free bottom half of the stack.
+       if(runtime·debug.efence || StackFromSystem) {
+               if(runtime·debug.efence || StackFaultOnFree)
+                       runtime·SysFault(oldstk, newsize);
+               else
+                       runtime·SysFree(oldstk, newsize, &mstats.stacks_sys);
+               return;
+       }
+       // First, we trick malloc into thinking
        // we allocated the stack as two separate half-size allocs.  Then the
        // free() call does the rest of the work for us.
        if(oldsize == PageSize) {