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runtime: eliminate poisonStack checks

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We haven't used poisonStack since we switched to 1-bit stack maps
(4d0f3a1), but the checks are still there. However, nothing prevents
us from genuinely allocating an object at this address on 32-bit and
causing the runtime to crash claiming that it's found a bad pointer.

Since we're not using poisonStack anyway, just pull it out.

Fixes #15831.

Change-Id: Ia6ef604675b8433f75045e369f5acd4644a5bb38
Reviewed-on: https://go-review.googlesource.com/24211
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Austin Clements 2016-06-17 11:07:56 -04:00
parent fca9fc52c8
commit 9e8fa1e99c
2 changed files with 3 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

4
src/runtime/mbarrier.go
View file

@ -145,7 +145,7 @@ func writebarrierptr(dst *uintptr, src uintptr) {
if !writeBarrier.needed { if !writeBarrier.needed {
return return
} }
if src != 0 && (src < sys.PhysPageSize || src == poisonStack) { if src != 0 && src < sys.PhysPageSize {
systemstack(func() { systemstack(func() {
print("runtime: writebarrierptr *", dst, " = ", hex(src), "\n") print("runtime: writebarrierptr *", dst, " = ", hex(src), "\n")
throw("bad pointer in write barrier") throw("bad pointer in write barrier")
@ -164,7 +164,7 @@ func writebarrierptr_nostore(dst *uintptr, src uintptr) {
if !writeBarrier.needed { if !writeBarrier.needed {
return return
} }
if src != 0 && (src < sys.PhysPageSize || src == poisonStack) { if src != 0 && src < sys.PhysPageSize {
systemstack(func() { throw("bad pointer in write barrier") }) systemstack(func() { throw("bad pointer in write barrier") })
} }
writebarrierptr_nostore1(dst, src) writebarrierptr_nostore1(dst, src)

3
src/runtime/stack.go
View file

@ -127,7 +127,6 @@ const (
const ( const (
uintptrMask = 1<<(8*sys.PtrSize) - 1 uintptrMask = 1<<(8*sys.PtrSize) - 1
poisonStack = uintptrMask & 0x6868686868686868
// Goroutine preemption request. // Goroutine preemption request.
// Stored into g->stackguard0 to cause split stack check failure. // Stored into g->stackguard0 to cause split stack check failure.
@ -594,7 +593,7 @@ func adjustpointers(scanp unsafe.Pointer, cbv *bitvector, adjinfo *adjustinfo, f
pp := (*uintptr)(add(scanp, i*sys.PtrSize)) pp := (*uintptr)(add(scanp, i*sys.PtrSize))
retry: retry:
p := *pp p := *pp
if f != nil && 0 < p && p < _PageSize && debug.invalidptr != 0 || p == poisonStack { if f != nil && 0 < p && p < _PageSize && debug.invalidptr != 0 {
// Looks like a junk value in a pointer slot. // Looks like a junk value in a pointer slot.
// Live analysis wrong? // Live analysis wrong?
getg().m.traceback = 2 getg().m.traceback = 2