Support prefix_symbols for linker

The linker needs to add __dl_ to the beginning of all of its symbols
to avoid conflicts.  Add support for a prefix_symbols property, and
insert an objcopy --prefix_symbols build step to produce the final
binary.

Change-Id: I70de7c830cd64305e5900c6de53efecea2e17c75

cc/builder.go

@@ -67,6 +67,13 @@ var (
 		},
 		"arCmd", "arFlags")
 
+	prefixSymbols = pctx.StaticRule("prefixSymbols",
+		blueprint.RuleParams{
+			Command:     "$objcopyCmd --prefix-symbols=${prefix} ${in} ${out}",
+			Description: "prefixSymbols $out",
+		},
+		"objcopyCmd", "prefix")
+
 	copyGccLibPath = pctx.StaticVariable("copyGccLibPath", "${SrcDir}/build/soong/copygcclib.sh")
 
 	copyGccLib = pctx.StaticRule("copyGccLib",
@@ -272,6 +279,24 @@ func TransformObjsToObj(ctx common.AndroidModuleContext, objFiles []string,
 	})
 }
 
+// Generate a rule for runing objcopy --prefix-symbols on a binary
+func TransformBinaryPrefixSymbols(ctx common.AndroidModuleContext, prefix string, inputFile string,
+	flags builderFlags, outputFile string) {
+
+	objcopyCmd := gccCmd(flags.toolchain, "objcopy")
+
+	ctx.Build(pctx, blueprint.BuildParams{
+		Rule:      prefixSymbols,
+		Outputs:   []string{outputFile},
+		Inputs:    []string{inputFile},
+		Implicits: []string{objcopyCmd},
+		Args: map[string]string{
+			"objcopyCmd": objcopyCmd,
+			"prefix":     prefix,
+		},
+	})
+}
+
 func CopyGccLib(ctx common.AndroidModuleContext, libName string,
 	flags builderFlags, outputFile string) {
 

cc/cc.go

@@ -1271,6 +1271,12 @@ func (c *CCBinary) compileModule(ctx common.AndroidModuleContext,
 
 	outputFile := filepath.Join(common.ModuleOutDir(ctx), c.getStem(ctx))
 	c.out = outputFile
+	if c.BinaryProperties.Prefix_symbols != "" {
+		afterPrefixSymbols := outputFile
+		outputFile = outputFile + ".intermediate"
+		TransformBinaryPrefixSymbols(ctx, c.BinaryProperties.Prefix_symbols, outputFile,
+			ccFlagsToBuilderFlags(flags), afterPrefixSymbols)
+	}
 
 	TransformObjToDynamicBinary(ctx, objFiles, deps.SharedLibs, deps.StaticLibs,
 		deps.LateStaticLibs, deps.WholeStaticLibs, deps.CrtBegin, deps.CrtEnd, true,