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From 1d1fa95c8ff7697e46343385a79a8f7e5c514a87 Mon Sep 17 00:00:00 2001
From: Zheng Xu <zheng.xu@linaro.org>
Date: Fri, 2 Sep 2016 17:40:05 +0800
Subject: [PATCH] Bug 1143022 - Manually mmap on arm64 to ensure high 17 bits
are clear. r=ehoogeveen
There might be 48-bit VA on arm64 depending on kernel configuration.
Manually mmap heap memory to align with the assumption made by JS engine.
Change-Id: Ic5d2b2fe4b758b3c87cc0688348af7e71a991146
Upstream-status: Backport
---
js/src/gc/Memory.cpp | 73 ++++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 71 insertions(+), 2 deletions(-)
diff --git a/js/src/gc/Memory.cpp b/js/src/gc/Memory.cpp
index e5ad018..4149adf 100644
--- a/js/src/gc/Memory.cpp
+++ b/js/src/gc/Memory.cpp
@@ -309,6 +309,75 @@ InitMemorySubsystem()
#endif
}
+static inline void *
+MapMemory(size_t length, int prot, int flags, int fd, off_t offset)
+{
+#if defined(__ia64__)
+ /*
+ * The JS engine assumes that all allocated pointers have their high 17 bits clear,
+ * which ia64's mmap doesn't support directly. However, we can emulate it by passing
+ * mmap an "addr" parameter with those bits clear. The mmap will return that address,
+ * or the nearest available memory above that address, providing a near-guarantee
+ * that those bits are clear. If they are not, we return NULL below to indicate
+ * out-of-memory.
+ *
+ * The addr is chosen as 0x0000070000000000, which still allows about 120TB of virtual
+ * address space.
+ *
+ * See Bug 589735 for more information.
+ */
+ void *region = mmap((void*)0x0000070000000000, length, prot, flags, fd, offset);
+ if (region == MAP_FAILED)
+ return MAP_FAILED;
+ /*
+ * If the allocated memory doesn't have its upper 17 bits clear, consider it
+ * as out of memory.
+ */
+ if ((uintptr_t(region) + (length - 1)) & 0xffff800000000000) {
+ JS_ALWAYS_TRUE(0 == munmap(region, length));
+ return MAP_FAILED;
+ }
+ return region;
+#elif defined(__aarch64__)
+ /*
+ * There might be similar virtual address issue on arm64 which depends on
+ * hardware and kernel configurations. But the work around is slightly
+ * different due to the different mmap behavior.
+ *
+ * TODO: Merge with the above code block if this implementation works for
+ * ia64 and sparc64.
+ */
+ const uintptr_t start = UINT64_C(0x0000070000000000);
+ const uintptr_t end = UINT64_C(0x0000800000000000);
+ const uintptr_t step = ChunkSize;
+ /*
+ * Optimization options if there are too many retries in practice:
+ * 1. Examine /proc/self/maps to find an available address. This file is
+ * not always available, however. In addition, even if we examine
+ * /proc/self/maps, we may still need to retry several times due to
+ * racing with other threads.
+ * 2. Use a global/static variable with lock to track the addresses we have
+ * allocated or tried.
+ */
+ uintptr_t hint;
+ void* region = MAP_FAILED;
+ for (hint = start; region == MAP_FAILED && hint + length <= end; hint += step) {
+ region = mmap((void*)hint, length, prot, flags, fd, offset);
+ if (region != MAP_FAILED) {
+ if ((uintptr_t(region) + (length - 1)) & 0xffff800000000000) {
+ if (munmap(region, length)) {
+ MOZ_ASSERT(errno == ENOMEM);
+ }
+ region = MAP_FAILED;
+ }
+ }
+ }
+ return region == MAP_FAILED ? NULL : region;
+#else
+ return mmap(NULL, length, prot, flags, fd, offset);
+#endif
+}
+
void *
MapAlignedPages(size_t size, size_t alignment)
{
@@ -322,12 +391,12 @@ MapAlignedPages(size_t size, size_t alignment)
/* Special case: If we want page alignment, no further work is needed. */
if (alignment == PageSize) {
- return mmap(NULL, size, prot, flags, -1, 0);
+ return MapMemory(size, prot, flags, -1, 0);
}
/* Overallocate and unmap the region's edges. */
size_t reqSize = Min(size + 2 * alignment, 2 * size);
- void *region = mmap(NULL, reqSize, prot, flags, -1, 0);
+ void *region = MapMemory(reqSize, prot, flags, -1, 0);
if (region == MAP_FAILED)
return NULL;
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