[LLD] [COFF] Allow setting subsystem versions while inferring the subsystem type implicitly

[mstorsjo]

Summary

Lead-up to a fix for PR42218.

[ruiu]

LGTM

lld/trunk/COFF/DriverUtils.cpp

void parseGuard(StringRef FullArg) {
   }
 }
 
 // Parses a string in the form of "<subsystem>[,<integer>[.<integer>]]".
 void parseSubsystem(StringRef Arg, WindowsSubsystem *Sys, uint32_t *Major,
                     uint32_t *Minor) {
   StringRef SysStr, Ver;
   std::tie(SysStr, Ver) = Arg.split(',');
-  *Sys = StringSwitch<WindowsSubsystem>(SysStr.lower())
+  std::string SysStrLower = SysStr.lower();
+  *Sys = StringSwitch<WindowsSubsystem>(SysStrLower)
     .Case("boot_application", IMAGE_SUBSYSTEM_WINDOWS_BOOT_APPLICATION)
     .Case("console", IMAGE_SUBSYSTEM_WINDOWS_CUI)
+    .Case("default", IMAGE_SUBSYSTEM_UNKNOWN)
     .Case("efi_application", IMAGE_SUBSYSTEM_EFI_APPLICATION)
     .Case("efi_boot_service_driver", IMAGE_SUBSYSTEM_EFI_BOOT_SERVICE_DRIVER)
     .Case("efi_rom", IMAGE_SUBSYSTEM_EFI_ROM)
     .Case("efi_runtime_driver", IMAGE_SUBSYSTEM_EFI_RUNTIME_DRIVER)
     .Case("native", IMAGE_SUBSYSTEM_NATIVE)
     .Case("posix", IMAGE_SUBSYSTEM_POSIX_CUI)
     .Case("windows", IMAGE_SUBSYSTEM_WINDOWS_GUI)
     .Default(IMAGE_SUBSYSTEM_UNKNOWN);
-  if (*Sys == IMAGE_SUBSYSTEM_UNKNOWN)
+  if (*Sys == IMAGE_SUBSYSTEM_UNKNOWN && SysStrLower != "default")
     fatal("unknown subsystem: " + SysStr);
   if (!Ver.empty())
     parseVersion(Ver, Major, Minor);
 }
 
 // Parse a string of the form of "<from>=<to>".
 // Results are directly written to Config.
 void parseAlternateName(StringRef S) {

lld/trunk/test/COFF/subsystem-inference.test

 # RUN: sed -e s/ENTRYNAME/main/ %s | yaml2obj > %t.obj
 # RUN: lld-link /out:%t.exe %t.obj
 # RUN: llvm-readobj --file-headers %t.exe | FileCheck -check-prefix=MAIN %s
+# RUN: lld-link /out:%t.exe %t.obj /subsystem:default,6.0
+# RUN: llvm-readobj --file-headers %t.exe | FileCheck -check-prefix=MAIN %s
 
 # RUN: sed s/ENTRYNAME/wmain/ %s | yaml2obj > %t.obj
 # RUN: lld-link /out:%t.exe %t.obj
 # RUN: llvm-readobj --file-headers %t.exe | FileCheck -check-prefix=WMAIN %s
 
 # RUN: sed s/ENTRYNAME/WinMain/ %s | yaml2obj > %t.obj
 # RUN: lld-link /out:%t.exe %t.obj
 # RUN: llvm-readobj --file-headers %t.exe | FileCheck -check-prefix=WINMAIN %s
+# RUN: lld-link /out:%t.exe %t.obj /subsystem:default,6.0
+# RUN: llvm-readobj --file-headers %t.exe | FileCheck -check-prefix=WINMAIN %s
 
 # RUN: sed s/ENTRYNAME/wWinMain/ %s | yaml2obj > %t.obj
 # RUN: lld-link /out:%t.exe %t.obj
 # RUN: llvm-readobj --file-headers %t.exe | FileCheck -check-prefix=WWINMAIN %s
 
 # MAIN:     Subsystem: IMAGE_SUBSYSTEM_WINDOWS_CUI
 # WMAIN:    Subsystem: IMAGE_SUBSYSTEM_WINDOWS_CUI
 # WINMAIN:  Subsystem: IMAGE_SUBSYSTEM_WINDOWS_GUI

lld/trunk/test/COFF/subsystem.test

 # RUN:   %p/Inputs/ret42.obj
 # RUN: llvm-readobj --file-headers %t.exe | FileCheck -check-prefix=CHECK2 %s
 
 CHECK2: MajorOperatingSystemVersion: 8
 CHECK2: MinorOperatingSystemVersion: 9
 CHECK2: MajorSubsystemVersion: 8
 CHECK2: MinorSubsystemVersion: 9
 CHECK2: Subsystem: IMAGE_SUBSYSTEM_WINDOWS_GUI
+
+# RUN: lld-link /entry:main /out:%t.exe /subsystem:default,8.9 \
+# RUN:   %p/Inputs/ret42.obj
+# RUN: llvm-readobj --file-headers %t.exe | FileCheck -check-prefix=CHECK3 %s
+
+CHECK3: MajorOperatingSystemVersion: 8
+CHECK3: MinorOperatingSystemVersion: 9
+CHECK3: MajorSubsystemVersion: 8
+CHECK3: MinorSubsystemVersion: 9