win: Add and use a custom CaptureContext() implementation

util/win/capture_context_test.cc

+// Copyright 2015 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 "util/win/capture_context.h"
+
+#include <stdint.h>
+
+#include <algorithm>
+
+#include "base/basictypes.h"
+#include "build/build_config.h"
+#include "gtest/gtest.h"
+
+namespace crashpad {
+namespace test {
+namespace {
+
+// 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(const CONTEXT& context) {
+#if defined(ARCH_CPU_X86)
+  const uint32_t must_have = CONTEXT_i386 |
+                             CONTEXT_CONTROL |
+                             CONTEXT_INTEGER |
+                             CONTEXT_SEGMENTS |
+                             CONTEXT_FLOATING_POINT;
+  ASSERT_EQ(must_have, context.ContextFlags & must_have);
+  const uint32_t may_have = CONTEXT_EXTENDED_REGISTERS;
+  ASSERT_EQ(0, context.ContextFlags & ~(must_have | may_have));
+#elif defined(ARCH_CPU_X86_64)
+  ASSERT_EQ(CONTEXT_AMD64 |
+            CONTEXT_CONTROL |
+            CONTEXT_INTEGER |
+            CONTEXT_SEGMENTS |
+            CONTEXT_FLOATING_POINT,
+            context.ContextFlags);
+#endif
+
+#if defined(ARCH_CPU_X86_FAMILY)
+  // Many bit positions in the flags register are reserved and will always read
+  // a known value. Most reserved 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 (253665-055),
+  // 3.4.3 “EFLAGS Register”, and AMD Architecture Programmer’s Manual, Volume
+  // 2: System Programming (24593-3.25), 3.1.6 “RFLAGS Register”.
+  EXPECT_EQ(2u, context.EFlags & 0xffc0802a);
+
+  // CaptureContext() doesn’t capture debug registers, so make sure they read 0.
+  EXPECT_EQ(0, context.Dr0);
+  EXPECT_EQ(0, context.Dr1);
+  EXPECT_EQ(0, context.Dr2);
+  EXPECT_EQ(0, context.Dr3);
+  EXPECT_EQ(0, context.Dr6);
+  EXPECT_EQ(0, context.Dr7);
+#endif
+
+#if defined(ARCH_CPU_X86)
+  // fxsave doesn’t write these bytes.
+  for (size_t i = 464; i < arraysize(context.ExtendedRegisters); ++i) {
+    SCOPED_TRACE(i);
+    EXPECT_EQ(0, context.ExtendedRegisters[i]);
+  }
+#elif defined(ARCH_CPU_X86_64)
+  // mxcsr shows up twice in the context structure. Make sure the values are
+  // identical.
+  EXPECT_EQ(context.MxCsr, context.FltSave.MxCsr);
+
+  // fxsave doesn’t write these bytes.
+  for (size_t i = 0; i < arraysize(context.FltSave.Reserved4); ++i) {
+    SCOPED_TRACE(i);
+    EXPECT_EQ(0, context.FltSave.Reserved4[i]);
+  }
+
+  // CaptureContext() doesn’t use these fields.
+  EXPECT_EQ(0, context.P1Home);
+  EXPECT_EQ(0, context.P2Home);
+  EXPECT_EQ(0, context.P3Home);
+  EXPECT_EQ(0, context.P4Home);
+  EXPECT_EQ(0, context.P5Home);
+  EXPECT_EQ(0, context.P6Home);
+  for (size_t i = 0; i < arraysize(context.VectorRegister); ++i) {
+    SCOPED_TRACE(i);
+    EXPECT_EQ(0, context.VectorRegister[i].Low);
+    EXPECT_EQ(0, context.VectorRegister[i].High);
+  }
+  EXPECT_EQ(0, context.VectorControl);
+  EXPECT_EQ(0, context.DebugControl);
+  EXPECT_EQ(0, context.LastBranchToRip);
+  EXPECT_EQ(0, context.LastBranchFromRip);
+  EXPECT_EQ(0, context.LastExceptionToRip);
+  EXPECT_EQ(0, context.LastExceptionFromRip);
+#endif
+}
+
+// A CPU-independent function to return the program counter.
+uintptr_t ProgramCounterFromContext(const CONTEXT& context) {
+#if defined(ARCH_CPU_X86)
+  return context.Eip;
+#elif defined(ARCH_CPU_X86_64)
+  return context.Rip;
+#endif
+}
+
+// A CPU-independent function to return the stack pointer.
+uintptr_t StackPointerFromContext(const CONTEXT& context) {
+#if defined(ARCH_CPU_X86)
+  return context.Esp;
+#elif defined(ARCH_CPU_X86_64)
+  return context.Rsp;
+#endif
+}
+
+void TestCaptureContext() {
+  CONTEXT context_1;
+  CaptureContext(&context_1);
+
+  {
+    SCOPED_TRACE("context_1");
+    ASSERT_NO_FATAL_FAILURE(SanityCheckContext(context_1));
+  }
+
+  // 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.
+  uintptr_t pc = ProgramCounterFromContext(context_1);
+
+  // 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;
+  CONTEXT 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");
+    ASSERT_NO_FATAL_FAILURE(SanityCheckContext(context_2));
+  }
+
+  EXPECT_EQ(sp, StackPointerFromContext(context_2));
+  EXPECT_GT(ProgramCounterFromContext(context_2), pc);
+}
+
+TEST(CaptureContextWin, CaptureContext) {
+  ASSERT_NO_FATAL_FAILURE(TestCaptureContext());
+}
+
+}  // namespace
+}  // namespace test
+}  // namespace crashpad