[lld] Accept -flavor FLAVOR anywhere on the command line

[gkm]

Summary

While developing the new MachO port of lld, we wish to select it via clang -Wl,-flavor,darwinnew .... The compiler driver does not place -Wl,... args at the front of the lld command line, so lld must accept it at locations beyond argv[1]

[gkm]

This comment was removed by gkm.

[gkm]

Add lld Driver tests

[MaskRay]

I think the problem here is that we should give thew new Darwin port a symlink like ld.lld, wasm-ld and lld-link.
Then we can teach clang to support -fuse-ld=foobar by locating the executable foobar (not ld.foobar as hard-coded by -fuse-ld=bfd -fuse-ld=gold -fuse-ld=lld) for non-ELF platforms. This requires a clang driver change.

I actually have a GCC patch sitting there for a while. https://gcc.gnu.org/pipermail/gcc-patches/2020-April/543324.html
I need to finish it.

[gkm]

True--this is no substitute for clang integration.
But meanwhile, is there harm in proceeding with this fix?

[gkm]

loosen expected output pattern for tests

[MaskRay]

In D80184#2044576, @gkm wrote:

True--this is no substitute for clang integration.
But meanwhile, is there harm in proceeding with this fix?

There is some little harm. In GNU ld, -flavor means --auxillary lavor.

I think using -Wl,-flavor,* to change the linker is weird. Let's see if -fuse-ld= can be fixed (D80225).

[gkm]

Fair enough.
How shall we name the new MachO lld?

[gkm]

We will fix the clang driver to invoke the proper alias for lld so that -flavor is unnecessary.

lld/docs/Driver.rst

 * core
 
 Selecting a Flavor
 ^^^^^^^^^^^^^^^^^^
 
 There are two different ways to tell lld which flavor to be. They are checked in
 order, so the second overrides the first. The first is to symlink :program:`lld`
 as :program:`lld-{flavor}` or just :program:`{flavor}`. You can also specify
-it as the first command line argument using ``-flavor``::
+it as a command line argument using ``-flavor {flavor}``::
 
   $ lld -flavor gnu
 
 There is a shortcut for ``-flavor core`` as ``-core``.
 
 
 Adding an Option to an existing Flavor
 ======================================

lld/test/Driver/flavor.test

+# RUN: not lld -v -flavor 2>&1 \
+# RUN:     | FileCheck --check-prefix=MISSING_ARG %s
+# RUN: not lld -flavor 2>&1 \
+# RUN:     | FileCheck --check-prefix=MISSING_ARG %s
+# RUN: not lld -flavor mystery 2>&1 \
+# RUN:     | FileCheck --check-prefix=MYSTERY %s
+
+# RUN: lld -v -flavor gnu \
+# RUN:     | FileCheck --check-prefix=GNU_V %s
+# RUN: lld -flavor gnu -v \
+# RUN:     | FileCheck --check-prefix=GNU_V %s
+# RUN: not lld -flavor gnu 2>&1 \
+# RUN:     | FileCheck --check-prefix=NO_INPUT_FILES %s
+# RUN: not lld -flavor ld 2>&1 \
+# RUN:     | FileCheck --check-prefix=NO_INPUT_FILES %s
+
+# RUN: not lld -flavor wasm 2>&1 \
+# RUN:     | FileCheck --check-prefix=NO_INPUT_FILES %s
+# RUN: not lld -flavor ld-wasm 2>&1 \
+# RUN:     | FileCheck --check-prefix=NO_INPUT_FILES %s
+
+# RUN: not lld -flavor link 2>&1 \
+# RUN:     | FileCheck --check-prefix=NO_INPUT_FILES %s
+
+# RUN: not lld -v -flavor darwin 2>&1 \
+# RUN:     | FileCheck --check-prefix=ARCH_NOT_SPECD %s
+# RUN: not lld -v -flavor ld64 2>&1 \
+# RUN:     | FileCheck --check-prefix=ARCH_NOT_SPECD %s
+
+# RUN: not lld -flavor darwinnew 2>&1 \
+# RUN:     | FileCheck --check-prefix=UNDEF_SYM_MAIN %s
+
+MISSING_ARG: missing arg value for '-flavor'
+MYSTERY: Unknown flavor: mystery
+NO_INPUT_FILES: lld: error: no input files
+UNDEF_SYM_MAIN: lld: error: undefined symbol: _main
+ARCH_NOT_SPECD: lld: error: -arch not specified and could not be inferred
+
+GNU_V: LLD {{[0-9.]+}} ({{.*}}) (compatible with GNU linkers)
+
+DARWINNEW: LLD {{[0-9.]+}} ({{.*}})
+DARWINNEW: Library search paths:
+DARWINNEW: /usr/lib
+DARWINNEW: /usr/local/lib

lld/tools/lld/lld.cpp

static Flavor parseProgname(StringRef progname) {
   for (StringRef s : v)
     if (Flavor f = getFlavor(s))
       return f;
   return Invalid;
 }
 
 static Flavor parseFlavor(std::vector<const char *> &v) {
   // Parse -flavor option.
-  if (v.size() > 1 && v[1] == StringRef("-flavor")) {
-    if (v.size() <= 2)
+  for (size_t i = 1; i < v.size(); i++) {
+    if (v[i] == StringRef("-flavor")) {
+      if (i + 1 == v.size())
         die("missing arg value for '-flavor'");
-    Flavor f = getFlavor(v[2]);
+      Flavor f = getFlavor(v[i + 1]);
       if (f == Invalid)
-      die("Unknown flavor: " + StringRef(v[2]));
-    v.erase(v.begin() + 1, v.begin() + 3);
+        die("Unknown flavor: " + StringRef(v[i + 1]));
+      v.erase(v.begin() + i, v.begin() + i + 2);
       return f;
     }
+  }
 
   // Deduct the flavor from argv[0].
   StringRef arg0 = path::filename(v[0]);
   if (arg0.endswith_lower(".exe"))
     arg0 = arg0.drop_back(4);
   return parseProgname(arg0);
 }