[LLD] [MinGW] Add support for --dynamicbase, ignore --nxcompat, --tsaware and --high-entropy-va

[mstorsjo]

Summary

All of these are disabled by default in GNU ld, but enabled by default in lld.

Disable dynamicbase by default since it potentially could cause compatibility issues, but just ignore the others since the lld default should be fine for most concievable cases.

[mstorsjo]

Added --high-entropy-va as well.

[mstorsjo]

Updated the options table and the tests to allow these options with a single dash as well.

[rnk]

Are all of these defaults important for mingw compatibility, or just -dynamicbase?

I really prefer LLD's defaults, which are inherited from MSVC. Users really shouldn't be making new PE images with executable data segments, or legacy pre-terminal server apps. We need to reserve the right to shed that cruft as time goes on. Microsoft accomplishes that by having very defined multi-year product cycles that are expected to have some migration cost. If the clang or gcc driver sets all these flags by default for the user, I don't care that much and I'd be OK with this patch.

[mstorsjo]

In D40017#925224, @rnk wrote:

Are all of these defaults important for mingw compatibility, or just -dynamicbase?

I really prefer LLD's defaults, which are inherited from MSVC. Users really shouldn't be making new PE images with executable data segments, or legacy pre-terminal server apps. We need to reserve the right to shed that cruft as time goes on. Microsoft accomplishes that by having very defined multi-year product cycles that are expected to have some migration cost. If the clang or gcc driver sets all these flags by default for the user, I don't care that much and I'd be OK with this patch.

Yeah, I would actually tend to agree with this - I'd rather have lld's defaults for those that are unlikely to actually have an impact in practice. And the probability that this will be the main issue for a user trying to link their mingw program with lld is pretty low since there's lots of other issues to run into anyway ;-)

Since there's no negative flag to use to disable it though, should we just ignore these options and pass nothing on to the coff driver, or should we just drop the negative defaults? I.e. if the user passed no option to the mingw driver, pass no flag to the coff driver (and implicitly use that default), if the user passed an option, pass a similar option onwards (even though it just reinforces the default)?

[rnk]

I think I'm in favor of ignoring options that reinforce LLD's defaults and don't have negatives. We can wait until a user files a bug and then add a negative option for them, or maybe add an escaping mechanism to let them pass the negative MSVC-style option.

[rnk]

lgtm

[ruiu]

LGTM

MinGW/Driver.cpp

159

nit: add a blank line so that this code block doesn't look like a series of if ~ else if ~ else if ~ else. Or maybe you could use :?

MinGW/Driver.cpp

bool mingw::link(ArrayRef<const char *> ArgsArr, raw_ostream &Diag) {
   if (Args.hasArg(OPT_verbose))
     Add("-verbose");
   if (Args.hasArg(OPT_export_all_symbols))
     Add("-export-all-symbols");
   if (!Args.hasArg(OPT_strip_all))
     Add("-debug:dwarf");
   if (Args.hasArg(OPT_large_address_aware))
     Add("-largeaddressaware");
+  if (Args.hasArg(OPT_dynamicbase))
+    Add("-dynamicbase");
+  else
+    Add("-dynamicbase:no");
 
   if (auto *A = Args.getLastArg(OPT_m)) {
     StringRef S = A->getValue();
     if (S == "i386pe")
       Add("-machine:x86");
     else if (S == "i386pep")
       Add("-machine:x64");
     else if (S == "thumb2pe")

MinGW/Options.td

 include "llvm/Option/OptParser.td"
 
 class F<string name>: Flag<["--", "-"], name>;
 class J<string name>: Joined<["--", "-"], name>;
 class S<string name>: Separate<["--", "-"], name>;
 
 def L: JoinedOrSeparate<["-"], "L">, MetaVarName<"<dir>">,
   HelpText<"Add a directory to the library search path">;
+def dynamicbase: F<"dynamicbase">, HelpText<"Enable ASLR">;
 def entry: S<"entry">, MetaVarName<"<entry>">,
   HelpText<"Name of entry point symbol">;
 def export_all_symbols: F<"export-all-symbols">,
     HelpText<"Export all symbols even if a def file or dllexport attributes are used">;
 def l: JoinedOrSeparate<["-"], "l">, MetaVarName<"<libName>">,
   HelpText<"Root name of library to use">;
 def m: JoinedOrSeparate<["-"], "m">, HelpText<"Set target emulation">;
 def no_whole_archive: F<"no-whole-archive">,

 
 // Currently stubs to avoid errors
 def Bdynamic: F<"Bdynamic">, HelpText<"Link against shared libraries">;
 def Bstatic: F<"Bstatic">, HelpText<"Do not link against shared libraries">;
 def O: Joined<["-"], "O">, HelpText<"Optimize output file size">;
 def enable_auto_image_base: F<"enable-auto-image-base">;
 def enable_auto_import: F<"enable-auto-import">;
 def full_shutdown: Flag<["--"], "full-shutdown">;
+def high_entropy_va: F<"high-entropy-va">, HelpText<"Enable 64-bit ASLR">;
 def major_image_version: S<"major-image-version">;
 def minor_image_version: S<"minor-image-version">;
+def nxcompat: F<"nxcompat">, HelpText<"Enable data execution prevention">;
 def sysroot: J<"sysroot">, HelpText<"Sysroot">;
+def tsaware: F<"tsaware">, HelpText<"Create Terminal Server aware executable">;
 def v: Flag<["-"], "v">, HelpText<"Display the version number">;
 def version: F<"version">, HelpText<"Display the version number and exit">;
 
 // Alias
 def alias_entry_e: JoinedOrSeparate<["-"], "e">, Alias<entry>;
 def alias_strip_s: Flag<["-"], "s">, Alias<strip_all>;

test/MinGW/driver.test

 DEBUG: -debug:dwarf
 
 RUN: ld.lld -### -m i386pep foo.o -s | FileCheck -check-prefix STRIP %s
 RUN: ld.lld -### -m i386pep foo.o --strip-all | FileCheck -check-prefix STRIP %s
 STRIP-NOT: -debug:dwarf
 
 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 i386pep foo.o | FileCheck -check-prefix DEFAULT-DISABLE-FLAGS %s
+DEFAULT-DISABLE-FLAGS: -dynamicbase:no
+
+# The extra '-' in the following check pattern is intentional, to make sure
+# that a check for "-dynamicbase" doesn't match the default "-dynamicbase:no".
+RUN: ld.lld -### -m i386pep foo.o --dynamicbase | FileCheck -check-prefix DYNAMICBASE %s
+RUN: ld.lld -### -m i386pep foo.o -dynamicbase | FileCheck -check-prefix DYNAMICBASE %s
+DYNAMICBASE: -dynamicbase -