Print out "suppoted targets" and "supported emulations".

[ruiu]

Summary

This is to improve compatibility with the GNU linkers for those
who expect these strings in a message for the -help option.

[ruiu]

I chose to print out all the targets and emulations that LLD actually supports, instead of printing out supported target: elf, because I found that the message is useful not only for Libtool-generated scripts but for human as well.

[emaste]

lld/ELF/DriverUtils.cpp

130–133 ↗

(On Diff #92540)

Is there some way we can ensure this list stays in sync with the ones LLD accepts? I think it would be too easy to forget to update this when adding a new target / emulation.

[ruiu]

lld/ELF/DriverUtils.cpp

130–133 ↗

(On Diff #92540)

Some target strings occur only here in the entire LLVM source code, I'd say there's no easy way to keep this string in sync with the actual behavior. But I think we don't need to worry too much about it because adding a new target is rather rare.

[ruiu]

• Do not print out "supported emulations".

[emaste]

lld/ELF/DriverUtils.cpp

124 ↗

(On Diff #92716)

Right now this will remain true for any upcoming libtool releases, so maybe we want to say something like Scripts generated by Libtool versions up to at least 2.4.6 expect ...?

lld/trunk/ELF/DriverUtils.cpp

opt::InputArgList ELFOptTable::parse(ArrayRef<const char *> Argv) {
   for (auto *Arg : Args.filtered(OPT_UNKNOWN))
     error("unknown argument: " + Arg->getSpelling());
   return Args;
 }
 
 void elf::printHelp(const char *Argv0) {
   ELFOptTable Table;
   Table.PrintHelp(outs(), Argv0, "lld", false);
+  outs() << "\n";
+
+  // Scripts generated by Libtool versions up to at least 2.4.6 (the most
+  // recent version as of March 2017) expect /supported targets:.* elf/ in
+  // a message for the -help option. If it doesn't match, the scripts
+  // assume that the linker doesn't support very basic features such as
+  // shared libraries. Therefore, we need to print out at least "elf".
+  // Here, we print out all the targets that we support.
+  outs() << Argv0 << ": supported targets: "
+         << "elf32-i386 elf32-iamcu elf32-littlearm elf32-powerpc "
+         << "elf32-tradbigmips elf32-tradlittlemips elf32-x86-64 "
+         << "elf64-amdgpu elf64-littleaarch64 elf64-powerpc "
+         << "elf64-tradbigmips elf64-tradlittlemips elf64-x86-64\n";
 }
 
 // Reconstructs command line arguments so that so that you can re-run
 // the same command with the same inputs. This is for --reproduce.
 std::string elf::createResponseFile(const opt::InputArgList &Args) {
   SmallString<0> Data;
   raw_svector_ostream OS(Data);
 

lld/trunk/test/ELF/driver.test

 # UNKNOWN: unable to find library -lnosuchlib
 
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
 # RUN: not ld.lld %t -o /no/such/file 2>&1 | FileCheck -check-prefix=MISSING %s
 # MISSING: cannot open output file /no/such/file
 
 # RUN: ld.lld --help 2>&1 | FileCheck -check-prefix=HELP %s
 # HELP: USAGE:
+# HELP: ld.lld: supported targets: {{.*}} elf
 
 # RUN: ld.lld --version 2>&1 | FileCheck -check-prefix=VERSION %s
 # VERSION: LLD {{.*}} (compatible with GNU linkers)
 
 # RUN: not ld.lld -v 2>&1 | FileCheck -check-prefix=VERSION %s
 
 ## Attempt to link DSO with -r
 # RUN: ld.lld -shared %t -o %t.so