win: Add memory map range intersection helper

util/win/process_info.cc

Index: util/win/process_info.cc
diff --git a/util/win/process_info.cc b/util/win/process_info.cc
index ed5262c7f7cc9d7f2d2958d3c7c74a1b69a7b9a6..a5e17acdc63b29968cb236ffebee9f62b385399b 100644
--- a/util/win/process_info.cc
+++ b/util/win/process_info.cc
@@ -16,6 +16,8 @@
 
 #include <winternl.h>
 
+#include <algorithm>
+
 #include "base/logging.h"
 #include "base/strings/stringprintf.h"
 #include "build/build_config.h"
@@ -292,6 +294,16 @@ ProcessInfo::Module::Module() : name(), dll_base(0), size(0), timestamp() {
 ProcessInfo::Module::~Module() {
 }
 
+ProcessInfo::MemoryInfo::MemoryInfo()
+    : base_address(0),
+      region_size(0),
+      allocation_base(0),
+      state(0),
+      allocation_protect(0),
+      protect(0),
+      type(0) {
+}
+
 ProcessInfo::MemoryInfo::MemoryInfo(const MEMORY_BASIC_INFORMATION& mbi)
     : base_address(reinterpret_cast<WinVMAddress>(mbi.BaseAddress)),
       region_size(mbi.RegionSize),
@@ -415,7 +427,74 @@ bool ProcessInfo::Modules(std::vector<Module>* modules) const {
 
 const std::vector<ProcessInfo::MemoryInfo>& ProcessInfo::MemoryInformation()
     const {
+  INITIALIZATION_STATE_DCHECK_VALID(initialized_);
   return memory_info_;
 }
 
+std::vector<CheckedRange<WinVMAddress, WinVMSize>>
+GetAccessibleRangesInMemoryMap(
+    WinVMAddress address,
+    WinVMSize size,
+    const std::vector<ProcessInfo::MemoryInfo>& memory_info) {
+  std::vector<ProcessInfo::MemoryInfo> overlapping;
+
+  using Range = CheckedRange<WinVMAddress, WinVMSize>;
+
+  // Find all the ranges that overlap the target range, maintaining their order.
+  for (const auto& mi : memory_info) {
+    if (mi.base_address + mi.region_size <= address)

[Mark Mentovai, 2015/09/29 21:35:50]

Optional, but since you’re using CheckedRange in here, it’s not unreasonable to
add a (tested) OverlapsRange method to that class and use it here.

[scottmg, 2015/09/30 17:40:26]

Done. (Sadly std::copy_if is more unwieldy than a plain loop.)

+      continue;
+    if (mi.base_address >= address + size)
+      continue;
+    overlapping.push_back(mi);
+  }
+
+  if (overlapping.empty())
+    return std::vector<Range>();
+
+  // For the first and last, trim to the boundary of the incoming range.
+  ProcessInfo::MemoryInfo& front = overlapping.front();
+  if (front.base_address < address) {

[Mark Mentovai, 2015/09/29 21:35:50]

Everything should be valid without this if, and without the one at line 464.

[scottmg, 2015/09/30 17:40:26]

Done.

+    WinVMAddress original_base = front.base_address;
+    front.base_address = address;
+    front.region_size = (original_base + front.region_size) - address;
+  }
+
+  ProcessInfo::MemoryInfo& back = overlapping.back();
+  if (back.base_address + back.region_size >= address + size) {
+    back.region_size = (address + size) - back.base_address;
+  }
+
+  // Discard all non-accessible.
+  overlapping.erase(std::remove_if(overlapping.begin(),

[Mark Mentovai, 2015/09/29 21:35:50]

I like seeing the standard library being used so nicely!

+                                   overlapping.end(),
+                                   [](const ProcessInfo::MemoryInfo& mi) {
+                                     return mi.state == MEM_FREE;
+                                   }),
+                    overlapping.end());
+
+  if (overlapping.empty())
+    return std::vector<Range>();
+
+  // Convert to return type.
+  std::vector<Range> as_ranges;
+  for (const auto& mi : overlapping) {
+    as_ranges.push_back(Range(mi.base_address, mi.region_size));

[Mark Mentovai, 2015/09/29 21:35:50]

You’re not actually using any of the checking features of CheckedRange.
Intentional? Put a comment at the “using” if so.

Since these numbers come from the OS and ought to be trustworthy, you can also
do some debug-mode DCHECK(range.IsValid()) to take advantage of the checking
features.

[scottmg, 2015/09/30 17:40:25]

Yeah, it was just a handy representation of a range. But added a few DCHECKs.

+  }
+
+  // Coalesce remaining regions.
+  std::vector<Range> result;
+  result.push_back(as_ranges[0]);
+  for (size_t i = 1; i < as_ranges.size(); ++i) {
+    if (result.back().end() == as_ranges[i].base()) {
+      result.back().SetRange(result.back().base(),
+                             result.back().size() + as_ranges[i].size());
+    } else {
+      result.push_back(as_ranges[i]);
+    }
+  }
+
+  return result;
+}
+
 }  // namespace crashpad