Fix size computation in WindowsResourceCOFFWriter::performFileLayout()

[inglorion]

Summary

We calculated the size of auxiliary sections as two coff_symbol16s,
instead of as a coff_symbol16 and a coff_aux_section_definition. This
caused us to allocate insufficient bytes, causing the linker to crash
on some resource files. This change fixes the computation.

Fixes PR35581.

[inglorion]

llvm/lib/Object/WindowsResource.cpp

378

The code that actually writes the bytes (and thus needs to match the size we compute here) is in WindowsResourceCOFFWriter::writeSymbolTable(), starting on line 511.

[ruiu]

Do you think you can add a test?

[pcc]

llvm/lib/Object/WindowsResource.cpp

379

Is this correct? I think the size of an auxiliary symbol is the same as the size of a regular symbol, so this looks like this would produce the same result as before.

[inglorion]

llvm/lib/Object/WindowsResource.cpp

379

You are right; they are both 18 bytes. And just changing the code as I've done here does not actually fix the problem. I had some printstrumentation in there that seems to make the difference between working and broken. This is getting more interesting.

[inglorion]

Superseded by D41270.

llvm/lib/Object/WindowsResource.cpp

void WindowsResourceCOFFWriter::performFileLayout() {
   FileSize += 2 * COFF::SectionSize;
 
   performSectionOneLayout();
   performSectionTwoLayout();
 
   // We have reached the address of the symbol table.
   SymbolTableOffset = FileSize;
 
-  FileSize += COFF::Symbol16Size;     // size of the @feat.00 symbol.
-  FileSize += 4 * COFF::Symbol16Size; // symbol + aux for each section.
-  FileSize += Data.size() * COFF::Symbol16Size; // 1 symbol per resource.
-  FileSize += 4; // four null bytes for the string table.
+  FileSize += 3 * COFF::Symbol16Size +          // @feat.00, .rsrc$1, .rsrc$2
+    2 * sizeof(coff_aux_section_definition) +   // first and second aux section
+    Data.size() * COFF::Symbol16Size +          // 1 symbol per resource
+    4;                                          // string table (4 nul bytes).
 }
 
 void WindowsResourceCOFFWriter::performSectionOneLayout() {
   SectionOneOffset = FileSize;
 
   SectionOneSize = Resources.getTreeSize();
   uint32_t CurrentStringOffset = SectionOneSize;
   uint32_t TotalStringTableSize = 0;