compiler: improve name mangling for packpaths

    
    The current implementation of Gogo::pkgpath_for_symbol was written in
    a way that allowed two distinct package paths to map to the same
    symbol, which could cause collisions at link- time or compile-time.
    
    Switch to a better mangling scheme to insure that we get a unique
    packagepath symbol for each package. In the new scheme instead of having
    separate mangling schemes for identifiers and package paths, the
    main identifier mangler ("go_encode_id") now handles mangling of
    both packagepath characters and identifier characters.
    
    The new mangling scheme is more intrusive: "foo/bar.Baz" is mangled as
    "foo..z2fbar.Baz" instead of "foo_bar.Baz". To mitigate this, this
    patch also adds a demangling capability so that function names
    returned from runtime.CallersFrames are converted back to their
    original unmangled form.
    
    Changing the pkgpath_for_symbol scheme requires updating a number of
    //go:linkname directives and C "__asm__" directives to match the new
    scheme, as well as updating the 'gotest' driver (which makes
    assumptions about the correct mapping from pkgpath symbol to package
    name).
    
    Fixes golang/go#27534.
    
    Reviewed-on: https://go-review.googlesource.com/c/135455

From-SVN: r265510

1 files changed, 4 insertions, 20 deletions

diff --git a/gcc/go/gofrontend/gogo.h b/gcc/go/gofrontend/gogo.h
index 9c469ca..48359eb 100644
--- a/gcc/go/gofrontend/gogo.h
+++ b/gcc/go/gofrontend/gogo.h
@@ -199,26 +199,10 @@ class Gogo
     return name.substr(1, name.rfind('.') - 1);
   }
 
-  // Given a name which may or may not have been hidden, return the
-  // name to use within a mangled symbol name.
-  static std::string
-  mangle_possibly_hidden_name(const std::string& name)
-  { 
-    // FIXME: This adds in pkgpath twice for hidden symbols, which is
-    // less than ideal.
-    std::string n;
-    if (!Gogo::is_hidden_name(name))
-      n = name;
-    else
-      {
-        n = ".";
-        std::string pkgpath = Gogo::hidden_name_pkgpath(name);
-        n.append(Gogo::pkgpath_for_symbol(pkgpath));
-        n.append(1, '.');
-        n.append(Gogo::unpack_hidden_name(name));
-      }
-    return n;
-  }
+  // Given a name which may or may not have been hidden, append the
+  // appropriate version of the name to the result string.
+  static void
+  append_possibly_hidden_name(std::string *result, const std::string& name);
 
   // Given a name which may or may not have been hidden, return the
   // name to use in an error message.