Rework how linux_bionic is built with LLD

In order to simplify the wrapper function, and stop using a linker
script, generate a set of flags to pass to LLD. Then run
host_bionic_inject on the linked binary in order to verify the
embedding, and give the wrapper function the address of the original
entry point (_start).

Bug: 31559095
Test: build host bionic with prebuilts/build-tools/build-prebuilts.sh
Change-Id: I53e326050e0f9caa562c6cf6f76c4d0337bb6faf

3 files changed, 214 insertions, 48 deletions

diff --git a/cmd/extract_linker/main.go b/cmd/extract_linker/main.go
index 3f24ab2d..ea0bf4ee 100644
--- a/cmd/extract_linker/main.go
+++ b/cmd/extract_linker/main.go
@@ -13,7 +13,7 @@
 // limitations under the License.
 
 // This tool extracts ELF LOAD segments from our linker binary, and produces an
-// assembly file and linker script which will embed those segments as sections
+// assembly file and linker flags which will embed those segments as sections
 // in another binary.
 package main
 
@@ -26,38 +26,15 @@ import (
 	"io/ioutil"
 	"log"
 	"os"
-	"text/template"
+	"strings"
 )
 
-var linkerScriptTemplate = template.Must(template.New("linker_script").Parse(`
-ENTRY(__dlwrap__start)
-SECTIONS {
-	__dlwrap_original_start = _start;
-	/DISCARD/ : { *(.interp) }
-
-{{range .}}
-	. = {{ printf "0x%x" .Vaddr }};
-	{{.Name}} : { KEEP(*({{.Name}})) }
-{{end}}
-
-	.text : { *(.text .text.*) }
-	.rodata : { *(.rodata .rodata.* .gnu.linkonce.r.*) }
-	.data : { *(.data .data.* .gnu.linkonce.d.*) }
-	.bss : { *(.dynbss) *(.bss .bss.* .gnu.linkonce.b.*) *(COMMON) }
-}
-`))
-
-type LinkerSection struct {
-	Name  string
-	Vaddr uint64
-}
-
 func main() {
 	var asmPath string
-	var scriptPath string
+	var flagsPath string
 
 	flag.StringVar(&asmPath, "s", "", "Path to save the assembly file")
-	flag.StringVar(&scriptPath, "T", "", "Path to save the linker script")
+	flag.StringVar(&flagsPath, "f", "", "Path to save the linker flags")
 	flag.Parse()
 
 	f, err := os.Open(flag.Arg(0))
@@ -72,19 +49,21 @@ func main() {
 	}
 
 	asm := &bytes.Buffer{}
-
-	fmt.Fprintln(asm, ".globl __dlwrap_linker_entry")
-	fmt.Fprintf(asm, ".set __dlwrap_linker_entry, 0x%x\n\n", ef.Entry)
-
 	baseLoadAddr := uint64(0x1000)
-	sections := []LinkerSection{}
 	load := 0
+	linkFlags := []string{}
+
+	fmt.Fprintln(asm, ".globl __dlwrap_linker_offset")
+	fmt.Fprintf(asm, ".set __dlwrap_linker_offset, 0x%x\n", baseLoadAddr)
+
 	for _, prog := range ef.Progs {
 		if prog.Type != elf.PT_LOAD {
 			continue
 		}
 
 		sectionName := fmt.Sprintf(".linker.sect%d", load)
+		symName := fmt.Sprintf("__dlwrap_linker_sect%d", load)
+
 		flags := ""
 		if prog.Flags&elf.PF_W != 0 {
 			flags += "w"
@@ -94,10 +73,12 @@ func main() {
 		}
 		fmt.Fprintf(asm, ".section %s, \"a%s\"\n", sectionName, flags)
 
-		if load == 0 {
-			fmt.Fprintln(asm, ".globl __dlwrap_linker_code_start")
-			fmt.Fprintln(asm, "__dlwrap_linker_code_start:")
-		}
+		fmt.Fprintf(asm, ".globl %s\n%s:\n\n", symName, symName)
+
+		linkFlags = append(linkFlags,
+			fmt.Sprintf("-Wl,--undefined=%s", symName),
+			fmt.Sprintf("-Wl,--section-start=%s=0x%x",
+				sectionName, baseLoadAddr+prog.Vaddr))
 
 		buffer, _ := ioutil.ReadAll(prog.Open())
 		bytesToAsm(asm, buffer)
@@ -113,11 +94,6 @@ func main() {
 		}
 		fmt.Fprintln(asm)
 
-		sections = append(sections, LinkerSection{
-			Name:  sectionName,
-			Vaddr: baseLoadAddr + prog.Vaddr,
-		})
-
 		load += 1
 	}
 
@@ -127,13 +103,10 @@ func main() {
 		}
 	}
 
-	if scriptPath != "" {
-		buf := &bytes.Buffer{}
-		if err := linkerScriptTemplate.Execute(buf, sections); err != nil {
-			log.Fatalf("Failed to create linker script: %v", err)
-		}
-		if err := ioutil.WriteFile(scriptPath, buf.Bytes(), 0777); err != nil {
-			log.Fatalf("Unable to write %q: %v", scriptPath, err)
+	if flagsPath != "" {
+		flags := strings.Join(linkFlags, " ")
+		if err := ioutil.WriteFile(flagsPath, []byte(flags), 0777); err != nil {
+			log.Fatalf("Unable to write %q: %v", flagsPath, err)
 		}
 	}
 }
diff --git a/cmd/host_bionic_inject/Android.bp b/cmd/host_bionic_inject/Android.bp
new file mode 100644
index 00000000..acce6838
--- /dev/null
+++ b/cmd/host_bionic_inject/Android.bp
@@ -0,0 +1,19 @@
+// Copyright 2018 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+blueprint_go_binary {
+    name: "host_bionic_inject",
+    deps: ["soong-symbol_inject"],
+    srcs: ["host_bionic_inject.go"],
+}
diff --git a/cmd/host_bionic_inject/host_bionic_inject.go b/cmd/host_bionic_inject/host_bionic_inject.go
new file mode 100644
index 00000000..0dabbba2
--- /dev/null
+++ b/cmd/host_bionic_inject/host_bionic_inject.go
@@ -0,0 +1,174 @@
+// Copyright 2018 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Verifies a host bionic executable with an embedded linker, then injects
+// the address of the _start function for the linker_wrapper to use.
+package main
+
+import (
+	"debug/elf"
+	"flag"
+	"fmt"
+	"io"
+	"os"
+
+	"android/soong/symbol_inject"
+)
+
+func main() {
+	var inputFile, linkerFile, outputFile string
+
+	flag.StringVar(&inputFile, "i", "", "Input file")
+	flag.StringVar(&linkerFile, "l", "", "Linker file")
+	flag.StringVar(&outputFile, "o", "", "Output file")
+	flag.Parse()
+
+	if inputFile == "" || linkerFile == "" || outputFile == "" || flag.NArg() != 0 {
+		flag.Usage()
+		os.Exit(1)
+	}
+
+	r, err := os.Open(inputFile)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err.Error())
+		os.Exit(2)
+	}
+	defer r.Close()
+
+	file, err := symbol_inject.OpenFile(r)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err.Error())
+		os.Exit(3)
+	}
+
+	linker, err := elf.Open(linkerFile)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err.Error())
+		os.Exit(4)
+	}
+
+	start_addr, err := parseElf(r, linker)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err.Error())
+		os.Exit(5)
+	}
+
+	w, err := os.OpenFile(outputFile, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0777)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err.Error())
+		os.Exit(6)
+	}
+	defer w.Close()
+
+	err = symbol_inject.InjectUint64Symbol(file, w, "__dlwrap_original_start", start_addr)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err.Error())
+		os.Exit(7)
+	}
+}
+
+// Check the ELF file, and return the address to the _start function
+func parseElf(r io.ReaderAt, linker *elf.File) (uint64, error) {
+	file, err := elf.NewFile(r)
+	if err != nil {
+		return 0, err
+	}
+
+	symbols, err := file.Symbols()
+	if err != nil {
+		return 0, err
+	}
+
+	for _, prog := range file.Progs {
+		if prog.Type == elf.PT_INTERP {
+			return 0, fmt.Errorf("File should not have a PT_INTERP header")
+		}
+	}
+
+	if dlwrap_start, err := findSymbol(symbols, "__dlwrap__start"); err != nil {
+		return 0, err
+	} else if dlwrap_start.Value != file.Entry {
+		return 0, fmt.Errorf("Expected file entry(0x%x) to point to __dlwrap_start(0x%x)",
+			file.Entry, dlwrap_start.Value)
+	}
+
+	err = checkLinker(file, linker, symbols)
+	if err != nil {
+		return 0, err
+	}
+
+	start, err := findSymbol(symbols, "_start")
+	if err != nil {
+		return 0, fmt.Errorf("Failed to find _start symbol")
+	}
+	return start.Value, nil
+}
+
+func findSymbol(symbols []elf.Symbol, name string) (elf.Symbol, error) {
+	for _, sym := range symbols {
+		if sym.Name == name {
+			return sym, nil
+		}
+	}
+	return elf.Symbol{}, fmt.Errorf("Failed to find symbol %q", name)
+}
+
+// Check that all of the PT_LOAD segments have been embedded properly
+func checkLinker(file, linker *elf.File, fileSyms []elf.Symbol) error {
+	dlwrap_linker_offset, err := findSymbol(fileSyms, "__dlwrap_linker_offset")
+	if err != nil {
+		return err
+	}
+
+	for i, lprog := range linker.Progs {
+		if lprog.Type != elf.PT_LOAD {
+			continue
+		}
+
+		found := false
+		for j, prog := range file.Progs {
+			if prog.Type != elf.PT_LOAD {
+				continue
+			}
+
+			if lprog.Vaddr+dlwrap_linker_offset.Value != prog.Vaddr {
+				continue
+			}
+			found = true
+
+			if lprog.Memsz != prog.Memsz {
+				return fmt.Errorf("Linker prog %d (0x%x) memsz (0x%x) does not match (0x%x)",
+					i, lprog.Vaddr, lprog.Memsz, prog.Memsz)
+			}
+
+			// The linker shouldn't be using BSS, since only one
+			// BSS section is supported per ELF file.
+			if prog.Memsz != prog.Filesz {
+				return fmt.Errorf("Embedded prog %d (0x%x) memsz (0x%x) does not match filesz (0x%x)",
+					j, prog.Vaddr, prog.Memsz, prog.Filesz)
+			}
+
+			if lprog.Flags != prog.Flags {
+				return fmt.Errorf("Linker prog %d (0x%x) flags (%s) do not match (%s)",
+					i, lprog.Vaddr, lprog.Flags, prog.Flags)
+			}
+		}
+		if !found {
+			return fmt.Errorf("Linker prog %d (0x%x) not found at offset 0x%x",
+				i, lprog.Vaddr, dlwrap_linker_offset.Value)
+		}
+	}
+
+	return nil
+}