COFF: Minor fix to Section size calculation

[loladiro]

Summary

I noticed llvm-dwarfdump was crashing on COFF dlls with embedded DWARF debug info. The reason was that SizeOfRawData actually indicates the size on disc which is not the size of the actual section data in a PE file (*.dll, *.exe), because of alignment rules. Instead the size of given by min(SizeOfRawData,VirtualSize).

I'm not sure what to do with respect to testing, since compiling a file from source would require a COFF capable linker. Is it acceptable to commit an entire PE exectuable to the repository? If so, I'll try to come up with a minimal example where this happens.

[echristo]

It is acceptable to put in a fully linked binary.

One more comment below.

Thanks!

lib/Object/COFFObjectFile.cpp

835

Instead of later on, how about a comment about "after linking"?

[loladiro]

Ok, I will come up with a test case test.

lib/Object/COFFObjectFile.cpp

835

Hmm, I intended it to mean, "later when LLVM is looking at the debug info". I see that this wording might be confusing. Will reword.

[loladiro]

Closed independently in r219388

lib/Object/COFFObjectFile.cpp

   // within the file bounds. We don't need to make sure it doesn't cover other
   // data, as there's nothing that says that is not allowed.
   uintptr_t ConStart = uintptr_t(base()) + Sec->PointerToRawData;
-  uintptr_t ConEnd = ConStart + Sec->SizeOfRawData;
+  // COFF requires sections to follow certain alignment rules in PE
+  // files. Thus (in a PE file) a section's actual data may be smaller
+  // than SizeOfRawData.
+  // Since for debug sections later on the actual data matters, we take
+  // the min of SizeOfRawData and VirtualSize which is the acutal size
+  // of the data.
+  uintptr_t Size = Sec->SizeOfRawData;
+  // COFF Object files always have VirtualSize set to 0
+  if (Sec->VirtualSize != 0)
+    Size = std::min(Size,(uintptr_t)Sec->VirtualSize);
+  uintptr_t ConEnd = ConStart + Size;
   if (ConEnd > uintptr_t(Data->getBufferEnd()))
     return object_error::parse_failed;
   Res = ArrayRef<uint8_t>(reinterpret_cast<const unsigned char*>(ConStart),
-                          Sec->SizeOfRawData);
+                          Size);
   return object_error::success;
 }