[LLD] [MinGW] Enable dynamicbase by default

[mstorsjo]

Summary

This matches lld-link's own default.

Add a new command line option --no-dynamicbase for disabling it. (Unfortunately, GNU ld doesn't yet have a matching --no-dynamicbase option, as that's the default there.)

[amccarth]

LGTM.

[mati865]

This really should have been the default for years but it didn't work properly with ld.bfd: https://github.com/msys2/MINGW-packages/issues/6674
Since it already work good with COFF backend when targeting MSVC I'm strongly in favour of enabling it for MinGW as well.

lld/MinGW/Driver.cpp

bool mingw::link(ArrayRef<const char *> argsArr, bool canExitEarly,
   if (args.hasArg(OPT_kill_at))
     add("-kill-at");
   if (args.hasArg(OPT_appcontainer))
     add("-appcontainer");
   if (args.hasArg(OPT_no_seh))
     add("-noseh");
 
   if (args.getLastArgValue(OPT_m) != "thumb2pe" &&
-      args.getLastArgValue(OPT_m) != "arm64pe" && !args.hasArg(OPT_dynamicbase))
+      args.getLastArgValue(OPT_m) != "arm64pe" &&
+      args.hasArg(OPT_no_dynamicbase))
     add("-dynamicbase:no");
 
   if (args.hasFlag(OPT_no_insert_timestamp, OPT_insert_timestamp, false))
     add("-timestamp:0");
 
   if (args.hasFlag(OPT_gc_sections, OPT_no_gc_sections, false))
     add("-opt:ref");
   else

lld/MinGW/Options.td

defm allow_multiple_definition: B<"allow-multiple-definition",
     "Allow multiple definitions",
     "Do not allow multiple definitions (default)">;
 def Bdynamic: F<"Bdynamic">, HelpText<"Link against shared libraries">;
 def Bstatic: F<"Bstatic">, HelpText<"Do not link against shared libraries">;
 def disable_auto_import: F<"disable-auto-import">,
     HelpText<"Don't automatically import data symbols from other DLLs without dllimport">;
 def disable_runtime_pseudo_reloc: F<"disable-runtime-pseudo-reloc">,
     HelpText<"Don't do automatic imports that require runtime fixups">;
-def dynamicbase: F<"dynamicbase">, HelpText<"Enable ASLR">;
+defm dynamicbase: B<"dynamicbase", "Enable ASLR", "Disable ASLR">;
 def enable_auto_import: F<"enable-auto-import">,
     HelpText<"Automatically import data symbols from other DLLs where needed">;
 def enable_runtime_pseudo_reloc: F<"enable-runtime-pseudo-reloc">,
     HelpText<"Allow automatic imports that require runtime fixups">;
 defm entry: Eq<"entry", "Name of entry point symbol">, MetaVarName<"<entry>">;
 def exclude_all_symbols: F<"exclude-all-symbols">,
     HelpText<"Don't automatically export any symbols">;
 def export_all_symbols: F<"export-all-symbols">,

lld/test/MinGW/driver.test

 
 RUN: ld.lld -### -m i386pep foo.o -pdb= | FileCheck -check-prefix PDB-DEFAULT %s
 PDB-DEFAULT: -debug
 PDB-DEFAULT-NOT: -pdb:{{.*}}
 
 RUN: ld.lld -### -m i386pep foo.o --large-address-aware | FileCheck -check-prefix LARGE-ADDRESS-AWARE %s
 LARGE-ADDRESS-AWARE: -largeaddressaware
 
-RUN: ld.lld -### -m i386pe foo.o | FileCheck -check-prefix DEFAULT-DISABLE-FLAGS %s
-RUN: ld.lld -### -m i386pep foo.o | FileCheck -check-prefix DEFAULT-DISABLE-FLAGS %s
-DEFAULT-DISABLE-FLAGS: -dynamicbase:no
-RUN: ld.lld -### -m i386pe --dynamicbase foo.o | FileCheck -check-prefix NO-DEFAULT-DISABLE-FLAGS %s
-RUN: ld.lld -### -m i386pep -dynamicbase foo.o | FileCheck -check-prefix NO-DEFAULT-DISABLE-FLAGS %s
-RUN: ld.lld -### -m thumb2pe foo.o | FileCheck -check-prefix NO-DEFAULT-DISABLE-FLAGS %s
-RUN: ld.lld -### -m arm64pe foo.o | FileCheck -check-prefix NO-DEFAULT-DISABLE-FLAGS %s
-NO-DEFAULT-DISABLE-FLAGS-NOT: -dynamicbase:no
+RUN: ld.lld -### -m i386pe foo.o --no-dynamicbase | FileCheck -check-prefix DISABLE-DYNAMICBASE %s
+DISABLE-DYNAMICBASE: -dynamicbase:no
+RUN: ld.lld -### -m i386pe --dynamicbase foo.o | FileCheck -check-prefix NO-DISABLE-DYNAMICBASE %s
+RUN: ld.lld -### -m i386pep -dynamicbase foo.o | FileCheck -check-prefix NO-DISABLE-DYNAMICBASE %s
+RUN: ld.lld -### -m i386pe foo.o | FileCheck -check-prefix NO-DISABLE-DYNAMICBASE %s
+RUN: ld.lld -### -m i386pep foo.o | FileCheck -check-prefix NO-DISABLE-DYNAMICBASE %s
+RUN: ld.lld -### -m thumb2pe foo.o | FileCheck -check-prefix NO-DISABLE-DYNAMICBASE %s
+RUN: ld.lld -### -m arm64pe foo.o | FileCheck -check-prefix NO-DISABLE-DYNAMICBASE %s
+# On arm, dynamicbase can't be disabled, so --no-dynamicbase is ignored
+RUN: ld.lld -### -m thumb2pe foo.o --no-dynamicbase | FileCheck -check-prefix NO-DISABLE-DYNAMICBASE %s
+RUN: ld.lld -### -m arm64pe foo.o --no-dynamicbase | FileCheck -check-prefix NO-DISABLE-DYNAMICBASE %s
+NO-DISABLE-DYNAMICBASE-NOT: -dynamicbase:no
 
 RUN: ld.lld -### -m i386pep foo.o --image-base 0x1230000 | FileCheck -check-prefix IMAGE-BASE %s
 RUN: ld.lld -### -m i386pep foo.o -image-base 0x1230000 | FileCheck -check-prefix IMAGE-BASE %s
 IMAGE-BASE: -base:0x1230000
 
 RUN: ld.lld -### -m i386pep foo.o | FileCheck -check-prefix NO-GC-SECTIONS %s
 RUN: ld.lld -### -m i386pep foo.o --gc-sections --no-gc-sections | FileCheck -check-prefix NO-GC-SECTIONS %s
 NO-GC-SECTIONS: -opt:noref