linux: work around LAHF bug in Flash

chrome/plugin/plugin_main_linux.cc

+// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#define _POSIX_SOURCE
+#include <signal.h>
+#include <string.h>
+
+#include "build/build_config.h"
+
+// This whole file is only useful on 64-bit architectures.
+#if defined(ARCH_CPU_64_BITS)
+
+namespace {
+
+// Signal handler for SIGILL; see WorkaroundFlashLAHF().
+void SignalHandler(int signal, siginfo_t* info, void* void_context) {
+  const char kLAHFInstruction = 0x9f;
+  if (signal != SIGILL ||
+      *reinterpret_cast<char*>(info->si_addr) != kLAHFInstruction) {
+    raise(signal);

[agl, 2010/01/04 23:02:43]

This may overflow the stack.

+    return;  // raise() should have killed us, but just in case...
+  }
+
+  ucontext_t* context = static_cast<ucontext_t*>(void_context);
+  greg_t* regs = context->uc_mcontext.gregs;
+  // LAHF moves the low byte of the EFLAGS register to AH.  Emulate that.
+  reinterpret_cast<char*>(&regs[REG_RAX])[1] =
+      reinterpret_cast<char*>(&regs[REG_EFL])[0];
+  // And advance the instruction pointer past the (one-byte) instruction.
+  ++regs[REG_RIP];
+}
+
+}  // namespace
+
+// 64-bit Flash sometimes uses the LAHF instruction which isn't
+// available on some CPUs.  We can work around it by catching SIGILL
+// (illegal instruction), checking if the signal was caused by this
+// particular circumstance, emulating the instruction, and resuming.
+// This function registers the signal handler.
+void WorkaroundFlashLAHF() {
+  struct sigaction action;
+  memset(&action, 0, sizeof(action));
+  action.sa_flags = SA_SIGINFO;
+  action.sa_sigaction = &SignalHandler;
+
+  sigaction(SIGILL, &action, NULL);
+}
+
+#endif  // defined(ARCH_CPU_64_BITS)