From c3ef56fa3239d9133be922059300a6fd2e7c1435 Mon Sep 17 00:00:00 2001
From: Zheng Xu <zheng.xu@linaro.org>
Date: Wed, 17 Aug 2016 11:59:15 +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
---

diff --git a/js/src/gc/Memory.cpp b/js/src/gc/Memory.cpp
index 153ccb4..b2d1311 100644
--- a/js/src/gc/Memory.cpp
+++ b/js/src/gc/Memory.cpp
@@ -339,6 +339,41 @@
         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 = (uintptr_t)(0x0000070000000000UL);
+    const uintptr_t end   = (uintptr_t)(0x0000800000000000UL);
+    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 ? nullptr : region;
 #else
     return mmap(NULL, length, prot, flags, fd, offset);
 #endif