Add CaptureContext and its test

client/capture_context_mac_test.cc

Index: client/capture_context_mac_test.cc
diff --git a/client/capture_context_mac_test.cc b/client/capture_context_mac_test.cc
new file mode 100644
index 0000000000000000000000000000000000000000..865fa44dbed22ad0226c842914a6c5b9a01aefd3
--- /dev/null
+++ b/client/capture_context_mac_test.cc
@@ -0,0 +1,154 @@
+// Copyright 2014 The Crashpad Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "client/capture_context_mac.h"
+
+#include <mach/mach.h>
+#include <stdint.h>
+
+#include <algorithm>
+
+#include "build/build_config.h"
+#include "gtest/gtest.h"
+
+namespace {
+
+using namespace crashpad;
+
+// If the context structure has fields that tell whether it’s valid, such as
+// magic numbers or size fields, sanity-checks those fields for validity with
+// fatal gtest assertions. For other fields, where it’s possible to reason about
+// their validity based solely on their contents, sanity-checks via nonfatal
+// gtest assertions.
+void SanityCheckContext(NativeCPUContext* context) {
+#if defined(ARCH_CPU_X86)
+  ASSERT_EQ(x86_THREAD_STATE32, context->tsh.flavor);
+  ASSERT_EQ(static_cast<int>(x86_THREAD_STATE32_COUNT), context->tsh.count);
+#elif defined(ARCH_CPU_X86_64)
+  ASSERT_EQ(x86_THREAD_STATE64, context->tsh.flavor);
+  ASSERT_EQ(static_cast<int>(x86_THREAD_STATE64_COUNT), context->tsh.count);
+#endif
+
+#if defined(ARCH_CPU_X86_FAMILY)
+  // The segment registers are only capable of storing 16-bit quantities, but
+  // the context structure provides native integer-width fields for them. Ensure
+  // that the high bits are all clear.
+  //
+  // Many bit positions in the flags register are reserved and will always read
+  // a known value. Most reservd bits are always 0, but bit 1 is always 1. Check
+  // that the reserved bits are all set to their expected values. Note that the
+  // set of reserved bits may be relaxed over time with newer CPUs, and that
+  // this test may need to be changed to reflect these developments. The current
+  // set of reserved bits are 1, 3, 5, 15, and 22 and higher. See Intel Software
+  // Developer’s Manual, Volume 1: Basic Architecture (253665-051), 3.4.3
+  // “EFLAGS Register”, and AMD Architecture Programmer’s Manual, Volume 2:
+  // System Programming (24593-2.53), 3.1.6 “RFLAGS Register”.
+#if defined(ARCH_CPU_X86)
+  EXPECT_EQ(0u, context->uts.ts32.__cs & ~0xffff);
+  EXPECT_EQ(0u, context->uts.ts32.__ds & ~0xffff);
+  EXPECT_EQ(0u, context->uts.ts32.__es & ~0xffff);
+  EXPECT_EQ(0u, context->uts.ts32.__fs & ~0xffff);
+  EXPECT_EQ(0u, context->uts.ts32.__gs & ~0xffff);
+  EXPECT_EQ(0u, context->uts.ts32.__ss & ~0xffff);
+  EXPECT_EQ(2u, context->uts.ts32.__eflags & 0xffc0802a);
+#elif defined(ARCH_CPU_X86_64)
+  EXPECT_EQ(0u, context->uts.ts64.__cs & ~UINT64_C(0xffff));
+  EXPECT_EQ(0u, context->uts.ts64.__fs & ~UINT64_C(0xffff));
+  EXPECT_EQ(0u, context->uts.ts64.__gs & ~UINT64_C(0xffff));
+  EXPECT_EQ(2u, context->uts.ts64.__rflags & UINT64_C(0xffffffffffc0802a));
+#endif
+#endif
+}
+
+// A CPU-independent function to return the program counter.
+uintptr_t ProgramCounterFromContext(NativeCPUContext* context) {
+#if defined(ARCH_CPU_X86)
+  return context->uts.ts32.__eip;
+#elif defined(ARCH_CPU_X86_64)
+  return context->uts.ts64.__rip;
+#endif
+}
+
+// A CPU-independent function to return the stack pointer.
+uintptr_t StackPointerFromContext(NativeCPUContext* context) {
+#if defined(ARCH_CPU_X86)
+  return context->uts.ts32.__esp;
+#elif defined(ARCH_CPU_X86_64)
+  return context->uts.ts64.__rsp;
+#endif
+}
+
+void TestCaptureContext() {
+  NativeCPUContext context_1;
+  CaptureContext(&context_1);
+
+  {
+    SCOPED_TRACE("context_1");
+    SanityCheckContext(&context_1);
+  }
+  if (testing::Test::HasFatalFailure()) {
+    return;
+  }
+
+  // The program counter reference value is this function’s address. The
+  // captured program counter should be slightly greater than or equal to the
+  // reference program counter.
+  const uintptr_t kReferencePC =
+      reinterpret_cast<uintptr_t>(TestCaptureContext);
+  uintptr_t pc = ProgramCounterFromContext(&context_1);
+  EXPECT_LT(pc - kReferencePC, 64u);
+
+  // Declare sp and context_2 here because all local variables need to be
+  // declared before computing the stack pointer reference value, so that the
+  // reference value can be the lowest value possible.
+  uintptr_t sp;
+  NativeCPUContext context_2;
+
+  // The stack pointer reference value is the lowest address of a local variable
+  // in this function. The captured program counter will be slightly less than
+  // or equal to the reference stack pointer.
+  const uintptr_t kReferenceSP =
+      std::min(std::min(reinterpret_cast<uintptr_t>(&context_1),
+                        reinterpret_cast<uintptr_t>(&context_2)),
+               std::min(reinterpret_cast<uintptr_t>(&pc),
+                        reinterpret_cast<uintptr_t>(&sp)));
+  sp = StackPointerFromContext(&context_1);
+  EXPECT_LT(kReferenceSP - sp, 512u);
+
+  // Capture the context again, expecting that the stack pointer stays the same
+  // and the program counter increases. Strictly speaking, there’s no guarantee
+  // that these conditions will hold, although they do for known compilers even
+  // under typical optimization.
+  CaptureContext(&context_2);
+
+  {
+    SCOPED_TRACE("context_2");
+    SanityCheckContext(&context_2);
+  }
+  if (testing::Test::HasFatalFailure()) {
+    return;
+  }
+
+  EXPECT_EQ(sp, StackPointerFromContext(&context_2));
+  EXPECT_GT(ProgramCounterFromContext(&context_2), pc);
+}
+
+TEST(CaptureContextMac, CaptureContext) {
+  TestCaptureContext();
+  if (Test::HasFatalFailure()) {
+    return;
+  }
+}
+
+}  // namespace