From 74bd6fcf57fcfa2edc070c5211dac1c3c109d076 Mon Sep 17 00:00:00 2001
From: Jim Chen <nchen@mozilla.com>
Date: Tue, 15 Jul 2014 12:45:40 -0400
Subject: [PATCH] Bug 1007824 - Add mfbt/LinuxSignal.h; r=snorp r=Ms2ger

---
 mfbt/LinuxSignal.h | 48 ++++++++++++++++++++++++++++++++++++++++++++++
 mfbt/moz.build     |  4 ++++
 2 files changed, 52 insertions(+)
 create mode 100644 mfbt/LinuxSignal.h

diff --git a/mfbt/LinuxSignal.h b/mfbt/LinuxSignal.h
new file mode 100644
index 00000000000..9b8e1bbbbe0
--- /dev/null
+++ b/mfbt/LinuxSignal.h
@@ -0,0 +1,48 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_LinuxSignal_h
+#define mozilla_LinuxSignal_h
+
+namespace mozilla {
+
+#if defined(__arm__)
+
+// Some (old) Linux kernels on ARM have a bug where a signal handler
+// can be called without clearing the IT bits in CPSR first. The result
+// is that the first few instructions of the handler could be skipped,
+// ultimately resulting in crashes. To workaround this bug, the handler
+// on ARM is a trampoline that starts with enough NOP instructions, so
+// that even if the IT bits are not cleared, only the NOP instructions
+// will be skipped over.
+
+template <void (*H)(int, siginfo_t*, void*)>
+__attribute__((naked)) void
+SignalTrampoline(int aSignal, siginfo_t* aInfo, void* aContext)
+{
+  asm volatile (
+    "nop; nop; nop; nop"
+    : : : "memory");
+
+  // Because the assembler may generate additional insturctions below, we
+  // need to ensure NOPs are inserted first by separating them out above.
+
+  asm volatile (
+    "bx %0"
+    :
+    : "r"(H), "l"(aSignal), "l"(aInfo), "l"(aContext)
+    : "memory");
+}
+
+# define MOZ_SIGNAL_TRAMPOLINE(h) (mozilla::SignalTrampoline<h>)
+
+#else // __arm__
+
+# define MOZ_SIGNAL_TRAMPOLINE(h) (h)
+
+#endif // __arm__
+
+} // namespace mozilla
+
+#endif // mozilla_LinuxSignal_h
diff --git a/mfbt/moz.build b/mfbt/moz.build
index 81f33ba2a79..90ef1aae540 100644
--- a/mfbt/moz.build
+++ b/mfbt/moz.build
@@ -78,6 +78,10 @@ if CONFIG['OS_ARCH'] == 'WINNT':
     EXPORTS.mozilla += [
         'WindowsVersion.h',
     ]
+elif CONFIG['OS_ARCH'] == 'Linux':
+    EXPORTS.mozilla += [
+        'LinuxSignal.h',
+    ]
 
 UNIFIED_SOURCES = [
     'double-conversion/bignum-dtoa.cc',