From 69ac4bd4218746255b079f33b8c8312b073cb582 Mon Sep 17 00:00:00 2001
From: Edwin Smith <smith@fb.com>
Date: Fri, 23 Oct 2015 08:07:21 -0700
Subject: [PATCH] Add VMRegAnchor before collect()

Summary: Otherwise vmregs are stale, and we'll miss roots when GC is entered
from JIT code. Also force callee-saved registers to spill so the
C++ stack scan will see them.

Reviewed By: ricklavoie

Differential Revision: D2572012

fb-gh-sync-id: a978f4c7795dd6ebf76466f965df02b84f1a5ec7
---
 hphp/runtime/base/heap-scan.h           | 1 +
 hphp/runtime/base/memory-manager-defs.h | 1 +
 hphp/runtime/base/thread-info.cpp       | 2 ++
 3 files changed, 4 insertions(+)

diff --git a/hphp/runtime/base/heap-scan.h b/hphp/runtime/base/heap-scan.h
index 4490beacf65..aed29d66c7a 100644
--- a/hphp/runtime/base/heap-scan.h
+++ b/hphp/runtime/base/heap-scan.h
@@ -269,6 +269,7 @@ template<class F> void scanRoots(F& mark) {
   TI().scan(mark);
   // C++ stack
   mark.where("cpp-stack");
+  asm volatile("" : : : "rbx", "r12", "r13", "r14", "r15");
   auto sp = stack_top_ptr();
   mark(sp, s_stackLimit + s_stackSize - uintptr_t(sp));
   // C++ threadlocal data, but don't scan MemoryManager
diff --git a/hphp/runtime/base/memory-manager-defs.h b/hphp/runtime/base/memory-manager-defs.h
index de3f5786638..014cc647004 100644
--- a/hphp/runtime/base/memory-manager-defs.h
+++ b/hphp/runtime/base/memory-manager-defs.h
@@ -187,6 +187,7 @@ template<class Fn> void BigHeap::iterate(Fn fn) {
       auto size = hdr->hdr_.kind == HeaderKind::Hole ||
                   hdr->hdr_.kind == HeaderKind::Free ? hdr->free_.size() :
                   MemoryManager::smallSizeClass(hdr->size());
+      assert(size % 16 == 0);
       hdr = (Header*)((char*)hdr + size);
       if (hdr >= slab_end) {
         assert(hdr == slab_end && "hdr > slab_end indicates corruption");
diff --git a/hphp/runtime/base/thread-info.cpp b/hphp/runtime/base/thread-info.cpp
index 682dbc7d6a6..fc5e7d3d84f 100644
--- a/hphp/runtime/base/thread-info.cpp
+++ b/hphp/runtime/base/thread-info.cpp
@@ -29,6 +29,7 @@
 #include "hphp/runtime/base/rds.h"
 #include "hphp/runtime/base/surprise-flags.h"
 #include "hphp/runtime/ext/process/ext_process.h"
+#include "hphp/runtime/vm/vm-regs.h"
 
 namespace HPHP {
 ///////////////////////////////////////////////////////////////////////////////
@@ -212,6 +213,7 @@ size_t check_request_surprise() {
     }
   }
   if (do_GC) {
+    VMRegAnchor _;
     MM().collect("surprise");
   }
   if (do_signaled) {
-- 
2.11.4.GIT