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runtime: fix bad pointer with 0 stack barriers

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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 <rlh@golang.org>
This commit is contained in:
Austin Clements 2016-10-23 21:53:44 -04:00
parent d1cc83472d
commit 3193c71c5b
1 changed files with 7 additions and 2 deletions
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9
src/runtime/stack.go
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@ -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))
}