[lld] [LLD][COFF] Add support for custom DOS stub (PR #122561)

[Hans Wennborg via llvm-commits]

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@@ -246,6 +246,21 @@ void LinkerDriver::parseAligncomm(StringRef s) {
       std::max(ctx.config.alignComm[std::string(name)], 1 << v);
 }
 
+void LinkerDriver::parseStub(StringRef path) {
+  std::unique_ptr<MemoryBuffer> stub =
+      CHECK(MemoryBuffer::getFile(path), "could not open " + path);
+  size_t bufferSize = stub->getBufferSize();
+  const char *bufferStart = stub->getBufferStart();
+  // MS link.exe compatibility:
+  // 1. stub must be greater or equal than 64 bytes
+  // 2. stub must be 8-byte aligned
+  // 3. stub must be start with a valid dos signature 'MZ'
+  if (bufferSize < 0x40 || bufferSize % 8 != 0 ||
+      (bufferStart[0] != 'M' || bufferStart[1] != 'Z'))
+    Err(ctx) << "/stub: invalid format for MS-DOS stub file: " << path;
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zmodem wrote:

It would be helpful if the error message could mention which requirement (size, signature, ..) failed.

(Useless trivia: 'zm' is also a valid dos .exe signature, but the windows loader doesn't like it: https://www.hanshq.net/making-executables.html#zm)

https://github.com/llvm/llvm-project/pull/122561