From 3193c71c5b97c1e770f587f50824b266f04b71d8 Mon Sep 17 00:00:00 2001 From: Austin Clements Date: Sun, 23 Oct 2016 21:53:44 -0400 Subject: [PATCH] runtime: fix bad pointer with 0 stack barriers Currently, if the number of stack barriers for a stack is 0, we'll create a zero-length slice that points just past the end of the stack allocation. This bad pointer causes GC panics. Fix this by creating a nil slice if the stack barrier count is 0. In practice, the only way this can happen is if GODEBUG=gcstackbarrieroff=1 is set because even the minimum size stack reserves space for two stack barriers. Change-Id: I3527c9a504c445b64b81170ee285a28594e7983d Reviewed-on: https://go-review.googlesource.com/31762 Reviewed-by: Rick Hudson --- src/runtime/stack.go | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/src/runtime/stack.go b/src/runtime/stack.go index 49499d4433..e803dc17a0 100644 --- a/src/runtime/stack.go +++ b/src/runtime/stack.go @@ -335,6 +335,7 @@ func stackalloc(n uint32) (stack, []stkbar) { // Compute the size of stack barrier array. maxstkbar := gcMaxStackBarriers(int(n)) nstkbar := unsafe.Sizeof(stkbar{}) * uintptr(maxstkbar) + var stkbarSlice slice if debug.efence != 0 || stackFromSystem != 0 { v := sysAlloc(round(uintptr(n), _PageSize), &memstats.stacks_sys) @@ -342,7 +343,9 @@ func stackalloc(n uint32) (stack, []stkbar) { throw("out of memory (stackalloc)") } top := uintptr(n) - nstkbar - stkbarSlice := slice{add(v, top), 0, maxstkbar} + if maxstkbar != 0 { + stkbarSlice = slice{add(v, top), 0, maxstkbar} + } return stack{uintptr(v), uintptr(v) + top}, *(*[]stkbar)(unsafe.Pointer(&stkbarSlice)) } @@ -410,7 +413,9 @@ func stackalloc(n uint32) (stack, []stkbar) { print(" allocated ", v, "\n") } top := uintptr(n) - nstkbar - stkbarSlice := slice{add(v, top), 0, maxstkbar} + if maxstkbar != 0 { + stkbarSlice = slice{add(v, top), 0, maxstkbar} + } return stack{uintptr(v), uintptr(v) + top}, *(*[]stkbar)(unsafe.Pointer(&stkbarSlice)) } -- 2.48.1