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, 5 insertions, 0 deletions

diff --git a/gcc/go/gofrontend/go-encode-id.h b/gcc/go/gofrontend/go-encode-id.h
index ec81b63..70126ba 100644
--- a/gcc/go/gofrontend/go-encode-id.h
+++ b/gcc/go/gofrontend/go-encode-id.h
@@ -20,6 +20,11 @@ go_id_needs_encoding(const std::string& str);
 extern std::string
 go_encode_id(const std::string &id);
 
+// Decodes an encoded ID, returning the original string handed off to
+// go_encode_id().
+extern std::string
+go_decode_id(const std::string &id);
+
 // Returns the empty string if the specified name needs encoding,
 // otherwise invokes go_encode_id on the name and returns the result.
 extern std::string