all: use ":" for compiler generated symbols

As it can't appear in user package paths.

There is a hack for handling "go:buildid" and "type:*" on windows/386.

Previously, windows/386 requires underscore prefix on external symbols,
but that's only applied for SHOSTOBJ/SUNDEFEXT or cgo export symbols.
"go.buildid" is STEXT, "type.*" is STYPE, thus they are not prefixed
with underscore.

In external linking mode, the external linker can't resolve them as
external symbols. But we are lucky that they have "." in their name,
so the external linker see them as Forwarder RVA exports. See:

 - https://docs.microsoft.com/en-us/windows/win32/debug/pe-format#export-address-table
 - https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=ld/pe-dll.c;h=e7b82ba6ffadf74dc1b9ee71dc13d48336941e51;hb=HEAD#l972)

This CL changes "." to ":" in symbols name, so theses symbols can not be
found by external linker anymore. So a hacky way is adding the
underscore prefix for these 2 symbols. I don't have enough knowledge to
verify whether adding the underscore for all STEXT/STYPE symbols are
fine, even if it could be, that would be done in future CL.

Fixes #37762

Change-Id: I92eaaf24c0820926a36e0530fdb07b07af1fcc35
Reviewed-on: https://go-review.googlesource.com/c/go/+/317917
Reviewed-by: Than McIntosh <thanm@google.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

1 files changed, 18 insertions, 1 deletions

diff --git a/src/cmd/compile/internal/base/link.go b/src/cmd/compile/internal/base/link.go
index 49fe4352b2..d8aa5a7dcc 100644
--- a/src/cmd/compile/internal/base/link.go
+++ b/src/cmd/compile/internal/base/link.go
@@ -8,6 +8,19 @@ import (
 	"cmd/internal/obj"
 )
 
+// ReservedImports are import paths used internally for generated
+// symbols by the compiler.
+//
+// The linker uses the magic symbol prefixes "go:" and "type:".
+// Avoid potential confusion between import paths and symbols
+// by rejecting these reserved imports for now. Also, people
+// "can do weird things in GOPATH and we'd prefer they didn't
+// do _that_ weird thing" (per rsc). See also #4257.
+var ReservedImports = map[string]bool{
+	"go":   true,
+	"type": true,
+}
+
 var Ctxt *obj.Link
 
 // TODO(mdempsky): These should probably be obj.Link methods.
@@ -20,7 +33,11 @@ func PkgLinksym(prefix, name string, abi obj.ABI) *obj.LSym {
 		// TODO(mdempsky): Cleanup callers and Fatalf instead.
 		return linksym(prefix, "_", abi)
 	}
-	return linksym(prefix, prefix+"."+name, abi)
+	sep := "."
+	if ReservedImports[prefix] {
+		sep = ":"
+	}
+	return linksym(prefix, prefix+sep+name, abi)
 }
 
 // Linkname returns the linker symbol for the given name as it might