Don't output a PDB unless /DEBUG is specified

[zturner]

Summary

Without this, someone can write lld-link.exe /OUT:foo.exe /OUT:foo.pdb foo.obj and it will generate a PDB. But it's not a very useful PDB, because .debug$S and .debug$T information is not put into the PDB unless /DEBUG is also specified from the command line. So, if /DEBUG is not specified, don't output anything.

[ruiu]

Is this behavior the same as the MSVC linker? If it doesn't make sense to pass the /pdb option without /debug, we might want to emit an error (or warning) in the driver.

[zturner]

Yes, MSVC ignores /pdb option if you don't pass /DEBUG.

D:\src\llvmbuild\pdbtest>cl /c /Z7 hello.cpp
Microsoft (R) C/C++ Optimizing Compiler Version 19.10.25019 for x86
Copyright (C) Microsoft Corporation.  All rights reserved.

hello.cpp
C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.10.25017\include\xlocale(314): warning C4530: C++ exception handler used, but unwind semantics are not enabled. Specify /EHsc
C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.10.25017\include\exception(366): warning C4577: 'noexcept' used with no exception handling mode specified; termination on exception is not guaranteed. Specify /EHsc

D:\src\llvmbuild\pdbtest>link /out:hello.exe /pdb:hello.pdb hello.obj
Microsoft (R) Incremental Linker Version 14.10.25019.0
Copyright (C) Microsoft Corporation.  All rights reserved.


D:\src\llvmbuild\pdbtest>dir hello*
 Volume in drive D is New Volume
 Volume Serial Number is 2EC5-6F01

 Directory of D:\src\llvmbuild\pdbtest

05/17/2017  04:05 PM                92 hello.cpp
05/17/2017  04:06 PM           183,296 hello.exe
05/17/2017  04:05 PM           334,693 hello.obj
               3 File(s)        518,081 bytes
               0 Dir(s)  129,495,351,296 bytes free

D:\src\llvmbuild\pdbtest>link /debug /out:hello.exe /pdb:hello.pdb hello.obj
Microsoft (R) Incremental Linker Version 14.10.25019.0
Copyright (C) Microsoft Corporation.  All rights reserved.


D:\src\llvmbuild\pdbtest>dir hello*
 Volume in drive D is New Volume
 Volume Serial Number is 2EC5-6F01

 Directory of D:\src\llvmbuild\pdbtest

05/17/2017  04:05 PM                92 hello.cpp
05/17/2017  04:06 PM           756,224 hello.exe
05/17/2017  04:06 PM         3,284,272 hello.ilk
05/17/2017  04:05 PM           334,693 hello.obj
05/17/2017  04:06 PM         8,048,640 hello.pdb
               5 File(s)     12,423,921 bytes
               0 Dir(s)  129,483,444,224 bytes free

[ruiu]

Thank you for verifying! LGTM.

[zturner]

Removed the /DEBUGPDB option since it is unreferenced in the code. If the intent is to force writing a PDB, then all you have to do is specify /DEBUG, and you are guaranteed to get a PDB.

Also added some tests confirming the interactions between /DEBUG and /PDB.

BTW, this page indicates that it's not just an accident that MSVC linker behaves this way.

Use /PDB:filename to specify the name of the PDB file. If /DEBUG is not specified, the /PDB option is ignored.

[ruiu]

LGTM

lld/test/COFF/pdb-options.test

21 ↗

(On Diff #99377)

Please fix.

lld/COFF/Writer.cpp

void Writer::run() {
   } else {
     writeHeader<pe32_header>();
   }
   fixSafeSEHSymbols();
   writeSections();
   sortExceptionTable();
   writeBuildId();
 
-  if (!Config->PDBPath.empty()) {
+  if (!Config->PDBPath.empty() && Config->Debug) {
     const llvm::codeview::DebugInfo *DI = nullptr;
     if (Config->DebugTypes & static_cast<unsigned>(coff::DebugType::CV))
       DI = BuildId->DI;
     createPDB(Config->PDBPath, Symtab, SectionTable, DI);
   }
 
   writeMapFile(OutputSections);