MEM_RESERVE regions are not accessible by ReadProcessMemory()

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 a0364cb59b6e58d3a8fcff89625eb1ac72837318..d34a34b3741c7b379f7eea1e9d644830a1caf400 100644
--- a/util/win/process_info.cc
+++ b/util/win/process_info.cc
@@ -107,11 +107,10 @@ bool ReadStruct(HANDLE process, WinVMAddress at, T* into) {
   return true;
 }
 
-bool RegionIsInaccessible(const ProcessInfo::MemoryInfo& memory_info) {
-  return memory_info.state == MEM_FREE ||
-         (memory_info.state == MEM_COMMIT &&
-          ((memory_info.protect & PAGE_NOACCESS) ||
-           (memory_info.protect & PAGE_GUARD)));
+bool RegionIsAccessible(const ProcessInfo::MemoryInfo& memory_info) {
+  return (memory_info.state == MEM_COMMIT &&
+          ((memory_info.protect & PAGE_NOACCESS) == 0 ||
+           (memory_info.protect & PAGE_GUARD) == 0));

[Mark Mentovai, 2015/10/01 20:51:09]

(Re your comment yesterday about PAGE_EXECUTE being readable)

Yeah, that’s an x86 thing, you can’t be executable without being readable. Other
CPUs are different, but since this code only runs on x86, it’s correct to not
mention PAGE_EXECUTE.

[scottmg, 2015/10/01 21:30:20]

Aha, make sense.

 }
 
 }  // namespace
@@ -468,7 +467,7 @@ std::vector<CheckedRange<WinVMAddress, WinVMSize>> GetReadableRangesOfMemoryMap(
   overlapping.erase(std::remove_if(overlapping.begin(),
                                    overlapping.end(),
                                    [](const ProcessInfo::MemoryInfo& mi) {
-                                     return RegionIsInaccessible(mi);
+                                     return !RegionIsAccessible(mi);
                                    }),
                     overlapping.end());
   if (overlapping.empty())