add unexported func name removing for tiny mode

internal/linker/linker.go

@@ -24,6 +24,7 @@ import (
 
 const (
 	MagicValueEnv = "GARBLE_LINKER_MAGIC"
+	TinyEnv       = "GARBLE_LINK_TINY"
 
 	cacheDirName   = "garble"
 	versionExt     = ".version"

internal/linker/patches/0002-add-unexported-function-name-removing.patch

@@ -0,0 +1,62 @@
+From fa9696c29047882eb54344ce911ecf02c7281247 Mon Sep 17 00:00:00 2001
+From: pagran <pagran@protonmail.com>
+Date: Mon, 9 Jan 2023 00:03:05 +0100
+Subject: [PATCH] add unexported function name removing
+
+---
+ cmd/link/internal/ld/pcln.go | 27 +++++++++++++++++++++++++++
+ 1 file changed, 27 insertions(+)
+
+diff --git a/cmd/link/internal/ld/pcln.go b/cmd/link/internal/ld/pcln.go
+index 1ec237ffc8..e1bea2032c 100644
+--- a/cmd/link/internal/ld/pcln.go
++++ b/cmd/link/internal/ld/pcln.go
+@@ -321,10 +321,19 @@ func (state *pclntab) generateFuncnametab(ctxt *Link, funcs []loader.Sym) map[lo
+ 		return name[:i], "[...]", name[j+1:]
+ 	}
+
++	garbleIsRemove := os.Getenv("GARBLE_LINK_TINY") == "true"
++
+ 	// Write the null terminated strings.
+ 	writeFuncNameTab := func(ctxt *Link, s loader.Sym) {
+ 		symtab := ctxt.loader.MakeSymbolUpdater(s)
++		if garbleIsRemove {
++			symtab.AddStringAt(0, "")
++		}
++
+ 		for s, off := range nameOffsets {
++			if garbleIsRemove && off == 0 {
++				continue
++			}
+ 			a, b, c := nameParts(ctxt.loader.SymName(s))
+ 			o := int64(off)
+ 			o = symtab.AddStringAt(o, a)
+@@ -335,7 +344,25 @@ func (state *pclntab) generateFuncnametab(ctxt *Link, funcs []loader.Sym) map[lo
+
+ 	// Loop through the CUs, and calculate the size needed.
+ 	var size int64
++
++	if garbleIsRemove {
++		size = 1 // first byte is reserved for empty string used for all non-exportable method names
++	}
++	garbleIsUnexported := func(s loader.Sym) bool {
++		name, _, _ := nameParts(ctxt.loader.SymName(s))
++		if name[len(name)-1] == '.' {
++			return true
++		}
++		c := name[strings.LastIndexByte(name, '.')+1]
++		return 'a' <= c && c <= 'z'
++	}
++
+ 	walkFuncs(ctxt, funcs, func(s loader.Sym) {
++		if garbleIsRemove && garbleIsUnexported(s) {
++			nameOffsets[s] = 0 // redirect name to empty string
++			return
++		}
++
+ 		nameOffsets[s] = uint32(size)
+ 		a, b, c := nameParts(ctxt.loader.SymName(s))
+ 		size += int64(len(a) + len(b) + len(c) + 1) // NULL terminate
+-- 
+2.38.1.windows.1
+

main.go

@@ -449,6 +449,9 @@ func mainErr(args []string) error {
 
 			executablePath = modifiedLinkPath
 			os.Setenv(linker.MagicValueEnv, strconv.FormatUint(uint64(magicValue()), 10))
+			if flagTiny {
+				os.Setenv(linker.TinyEnv, "true")
+			}
 
 			log.Printf("replaced linker with: %s", executablePath)
 		}

testdata/script/tiny.txtar

@@ -11,7 +11,8 @@ stderr '^caller: \?\? 1$' # position info is removed
 stderr '^recovered: ya like jazz?'
 ! stderr '^init runtime'  # GODEBUG prints are hidden, like inittrace=1
 ! stderr 'panic: oh noes' # panics are hidden
-
+stderr 'funcExported false funcUnexported true'
+stderr 'funcStructExported false funcStructUnexported true'
 
 [short] stop # no need to verify this with -short
 
@@ -21,16 +22,41 @@ garble build
 stderr '^caller: [0-9a-zA-Z_]+\.go [1-9]'
 stderr '^recovered: ya like jazz?'
 stderr 'panic: oh noes'
+stderr 'funcExported false funcUnexported false'
+stderr 'funcStructExported false funcStructUnexported false'
 -- go.mod --
 module test/main
 
 go 1.19
 -- garble_main.go --
 package main
 
-import "runtime"
+import (
+	"reflect"
+	"runtime"
+)
+
+type testStruct struct {}
+
+func (testStruct) unexportedFunc() { println("dummy") }
+
+func (testStruct) ExportedFunc() { println("dummy") }
+
+func ExportedFunc() { println("dummy") }
+
+func unexportedFunc() { println("dummy") }
+
+func isEmptyFuncName(i interface{}) bool {
+	name := runtime.FuncForPC(reflect.ValueOf(i).Pointer()).Name()
+	return len(name) == 0
+}
 
 func main() {
+	println("funcExported", isEmptyFuncName(ExportedFunc), "funcUnexported", isEmptyFuncName(unexportedFunc))
+
+	var s testStruct
+	println("funcStructExported", isEmptyFuncName(s.ExportedFunc), "funcStructUnexported", isEmptyFuncName(s.unexportedFunc))
+
 	var v any = "tada"
 	println(v)