[PATCH] D66420: Be explicit about Windows coff name trailing character policy

[serge via Phabricator via llvm-commits]

serge-sans-paille created this revision.
serge-sans-paille added reviewers: thakis, ecbeckmann.
serge-sans-paille added a project: LLVM.
Herald added subscribers: llvm-commits, hiraditya.

It's okay to *not* copy the trailing zero of a windows section/symbol name.
This is compatible with strncpy behavior but gcc doesn't know that and
throws an invalid warning. Encode this behavior in a proper function.

Ref: https://docs.microsoft.com/en-us/windows/win32/debug/pe-format#section-table-section-headers
and https://docs.microsoft.com/en-us/windows/win32/debug/pe-format#symbol-name-representation


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D66420

Files:
  llvm/lib/Object/WindowsResource.cpp


Index: llvm/lib/Object/WindowsResource.cpp
===================================================================
--- llvm/lib/Object/WindowsResource.cpp
+++ llvm/lib/Object/WindowsResource.cpp
@@ -515,6 +515,17 @@
   return std::move(OutputBuffer);
 }
 
+// According to COFF specification, if the Src has a size equal to Dest,
+// it's okay to *not* copy the trailing zero.
+template <size_t DestSize>
+static void coffnamecpy(char (&Dest)[DestSize], char const *Src) {
+  static_assert(DestSize <= COFF::NameSize, "Dest is large enough");
+  assert(strlen(Src) <= DestSize && "Dest is larger than Src");
+  assert(strlen(Src) <= COFF::NameSize &&
+         "Src is not larger than COFF::NameSize");
+  strncpy(Dest, Src, (size_t)COFF::NameSize);
+}
+
 void WindowsResourceCOFFWriter::writeCOFFHeader(uint32_t TimeDateStamp) {
   // Write the COFF header.
   auto *Header = reinterpret_cast<coff_file_header *>(BufferStart);
@@ -534,7 +545,7 @@
   CurrentOffset += sizeof(coff_file_header);
   auto *SectionOneHeader =
       reinterpret_cast<coff_section *>(BufferStart + CurrentOffset);
-  strncpy(SectionOneHeader->Name, ".rsrc$01", (size_t)COFF::NameSize);
+  coffnamecpy(SectionOneHeader->Name, ".rsrc$01");
   SectionOneHeader->VirtualSize = 0;
   SectionOneHeader->VirtualAddress = 0;
   SectionOneHeader->SizeOfRawData = SectionOneSize;
@@ -552,7 +563,7 @@
   CurrentOffset += sizeof(coff_section);
   auto *SectionTwoHeader =
       reinterpret_cast<coff_section *>(BufferStart + CurrentOffset);
-  strncpy(SectionTwoHeader->Name, ".rsrc$02", (size_t)COFF::NameSize);
+  coffnamecpy(SectionTwoHeader->Name, ".rsrc$02");
   SectionTwoHeader->VirtualSize = 0;
   SectionTwoHeader->VirtualAddress = 0;
   SectionTwoHeader->SizeOfRawData = SectionTwoSize;
@@ -590,7 +601,7 @@
   // Now write the symbol table.
   // First, the feat symbol.
   auto *Symbol = reinterpret_cast<coff_symbol16 *>(BufferStart + CurrentOffset);
-  strncpy(Symbol->Name.ShortName, "@feat.00", (size_t)COFF::NameSize);
+  coffnamecpy(Symbol->Name.ShortName, "@feat.00");
   Symbol->Value = 0x11;
   Symbol->SectionNumber = 0xffff;
   Symbol->Type = COFF::IMAGE_SYM_DTYPE_NULL;
@@ -600,7 +611,7 @@
 
   // Now write the .rsrc1 symbol + aux.
   Symbol = reinterpret_cast<coff_symbol16 *>(BufferStart + CurrentOffset);
-  strncpy(Symbol->Name.ShortName, ".rsrc$01", (size_t)COFF::NameSize);
+  coffnamecpy(Symbol->Name.ShortName, ".rsrc$01");
   Symbol->Value = 0;
   Symbol->SectionNumber = 1;
   Symbol->Type = COFF::IMAGE_SYM_DTYPE_NULL;
@@ -619,7 +630,7 @@
 
   // Now write the .rsrc2 symbol + aux.
   Symbol = reinterpret_cast<coff_symbol16 *>(BufferStart + CurrentOffset);
-  strncpy(Symbol->Name.ShortName, ".rsrc$02", (size_t)COFF::NameSize);
+  coffnamecpy(Symbol->Name.ShortName, ".rsrc$02");
   Symbol->Value = 0;
   Symbol->SectionNumber = 2;
   Symbol->Type = COFF::IMAGE_SYM_DTYPE_NULL;
@@ -640,7 +651,7 @@
   for (unsigned i = 0; i < Data.size(); i++) {
     auto RelocationName = formatv("$R{0:X-6}", i & 0xffffff).sstr<COFF::NameSize>();
     Symbol = reinterpret_cast<coff_symbol16 *>(BufferStart + CurrentOffset);
-    memcpy(Symbol->Name.ShortName, RelocationName.data(), (size_t) COFF::NameSize);
+    coffnamecpy(Symbol->Name.ShortName, RelocationName.data());
     Symbol->Value = DataOffsets[i];
     Symbol->SectionNumber = 2;
     Symbol->Type = COFF::IMAGE_SYM_DTYPE_NULL;


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