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
diff --git a/Android.bp b/Android.bp
index bdc34d0..bcf831d 100644
--- a/Android.bp
+++ b/Android.bp
@@ -482,7 +482,7 @@
}
cc_genrule {
- name: "host_bionic_linker_script",
+ name: "host_bionic_linker_flags",
host_supported: true,
device_supported: false,
target: {
@@ -497,7 +497,7 @@
},
},
tools: ["extract_linker"],
- cmd: "$(location) -T $(out) $(in)",
+ cmd: "$(location) -f $(out) $(in)",
srcs: [":linker"],
- out: ["linker.script"],
+ out: ["linker.flags"],
}
diff --git a/cc/binary.go b/cc/binary.go
index 5fa501e..15db2ad 100644
--- a/cc/binary.go
+++ b/cc/binary.go
@@ -15,6 +15,8 @@
package cc
import (
+ "github.com/google/blueprint"
+
"android/soong/android"
)
@@ -154,7 +156,8 @@
}
if ctx.Os() == android.LinuxBionic && !binary.static() {
- deps.LinkerScript = "host_bionic_linker_script"
+ deps.DynamicLinker = "linker"
+ deps.LinkerFlagsFile = "host_bionic_linker_flags"
}
}
@@ -244,14 +247,23 @@
switch ctx.Os() {
case android.Android:
flags.DynamicLinker = "/system/bin/linker"
+ if flags.Toolchain.Is64Bit() {
+ flags.DynamicLinker += "64"
+ }
case android.LinuxBionic:
flags.DynamicLinker = ""
default:
ctx.ModuleErrorf("unknown dynamic linker")
}
- if flags.Toolchain.Is64Bit() {
- flags.DynamicLinker += "64"
- }
+ }
+
+ if ctx.Os() == android.LinuxBionic {
+ // Use the dlwrap entry point, but keep _start around so
+ // that it can be used by host_bionic_inject
+ flags.LdFlags = append(flags.LdFlags,
+ "-Wl,--entry=__dlwrap__start",
+ "-Wl,--undefined=_start",
+ )
}
}
@@ -262,7 +274,6 @@
"-Wl,--gc-sections",
"-Wl,-z,nocopyreloc",
)
-
}
} else {
if binary.static() {
@@ -288,13 +299,15 @@
sharedLibs := deps.SharedLibs
sharedLibs = append(sharedLibs, deps.LateSharedLibs...)
- if deps.LinkerScript.Valid() {
- flags.LdFlags = append(flags.LdFlags, "-Wl,-T,"+deps.LinkerScript.String())
- linkerDeps = append(linkerDeps, deps.LinkerScript.Path())
+ if deps.LinkerFlagsFile.Valid() {
+ flags.LdFlags = append(flags.LdFlags, "$$(cat "+deps.LinkerFlagsFile.String()+")")
+ linkerDeps = append(linkerDeps, deps.LinkerFlagsFile.Path())
}
if flags.DynamicLinker != "" {
- flags.LdFlags = append(flags.LdFlags, " -Wl,-dynamic-linker,"+flags.DynamicLinker)
+ flags.LdFlags = append(flags.LdFlags, "-Wl,-dynamic-linker,"+flags.DynamicLinker)
+ } else if ctx.toolchain().Bionic() && !binary.static() {
+ flags.LdFlags = append(flags.LdFlags, "-Wl,--no-dynamic-linker")
}
builderFlags := flagsToBuilderFlags(flags)
@@ -323,6 +336,17 @@
binary.injectVersionSymbol(ctx, outputFile, versionedOutputFile)
}
+ if ctx.Os() == android.LinuxBionic && !binary.static() {
+ injectedOutputFile := outputFile
+ outputFile = android.PathForModuleOut(ctx, "prelinker", fileName)
+
+ if !deps.DynamicLinker.Valid() {
+ panic("Non-static host bionic modules must have a dynamic linker")
+ }
+
+ binary.injectHostBionicLinkerSymbols(ctx, outputFile, deps.DynamicLinker.Path(), injectedOutputFile)
+ }
+
linkerDeps = append(linkerDeps, deps.SharedLibsDeps...)
linkerDeps = append(linkerDeps, deps.LateSharedLibsDeps...)
linkerDeps = append(linkerDeps, objs.tidyFiles...)
@@ -367,3 +391,26 @@
func (binary *binaryDecorator) hostToolPath() android.OptionalPath {
return binary.toolPath
}
+
+func init() {
+ pctx.HostBinToolVariable("hostBionicSymbolsInjectCmd", "host_bionic_inject")
+}
+
+var injectHostBionicSymbols = pctx.AndroidStaticRule("injectHostBionicSymbols",
+ blueprint.RuleParams{
+ Command: "$hostBionicSymbolsInjectCmd -i $in -l $linker -o $out",
+ CommandDeps: []string{"$hostBionicSymbolsInjectCmd"},
+ }, "linker")
+
+func (binary *binaryDecorator) injectHostBionicLinkerSymbols(ctx ModuleContext, in, linker android.Path, out android.WritablePath) {
+ ctx.Build(pctx, android.BuildParams{
+ Rule: injectHostBionicSymbols,
+ Description: "inject host bionic symbols",
+ Input: in,
+ Implicit: linker,
+ Output: out,
+ Args: map[string]string{
+ "linker": linker.String(),
+ },
+ })
+}
diff --git a/cc/cc.go b/cc/cc.go
index 6320b9c..8b68489 100644
--- a/cc/cc.go
+++ b/cc/cc.go
@@ -83,7 +83,10 @@
ReexportGeneratedHeaders []string
CrtBegin, CrtEnd string
- LinkerScript string
+
+ // Used for host bionic
+ LinkerFlagsFile string
+ DynamicLinker string
}
type PathDeps struct {
@@ -108,7 +111,12 @@
// Paths to crt*.o files
CrtBegin, CrtEnd android.OptionalPath
- LinkerScript android.OptionalPath
+
+ // Path to the file container flags to use with the linker
+ LinkerFlagsFile android.OptionalPath
+
+ // Path to the dynamic linker binary
+ DynamicLinker android.OptionalPath
}
type Flags struct {
@@ -306,7 +314,8 @@
objDepTag = dependencyTag{name: "obj"}
crtBeginDepTag = dependencyTag{name: "crtbegin"}
crtEndDepTag = dependencyTag{name: "crtend"}
- linkerScriptDepTag = dependencyTag{name: "linker script"}
+ linkerFlagsDepTag = dependencyTag{name: "linker flags file"}
+ dynamicLinkerDepTag = dependencyTag{name: "dynamic linker"}
reuseObjTag = dependencyTag{name: "reuse objects"}
ndkStubDepTag = dependencyTag{name: "ndk stub", library: true}
ndkLateStubDepTag = dependencyTag{name: "ndk late stub", library: true}
@@ -1062,8 +1071,11 @@
if deps.CrtEnd != "" {
actx.AddVariationDependencies(nil, crtEndDepTag, deps.CrtEnd)
}
- if deps.LinkerScript != "" {
- actx.AddDependency(c, linkerScriptDepTag, deps.LinkerScript)
+ if deps.LinkerFlagsFile != "" {
+ actx.AddDependency(c, linkerFlagsDepTag, deps.LinkerFlagsFile)
+ }
+ if deps.DynamicLinker != "" {
+ actx.AddDependency(c, dynamicLinkerDepTag, deps.DynamicLinker)
}
version := ctx.sdkVersion()
@@ -1257,13 +1269,13 @@
} else {
ctx.ModuleErrorf("module %q is not a genrule", depName)
}
- case linkerScriptDepTag:
+ case linkerFlagsDepTag:
if genRule, ok := dep.(genrule.SourceFileGenerator); ok {
files := genRule.GeneratedSourceFiles()
if len(files) == 1 {
- depPaths.LinkerScript = android.OptionalPathForPath(files[0])
+ depPaths.LinkerFlagsFile = android.OptionalPathForPath(files[0])
} else if len(files) > 1 {
- ctx.ModuleErrorf("module %q can only generate a single file if used for a linker script", depName)
+ ctx.ModuleErrorf("module %q can only generate a single file if used for a linker flag file", depName)
}
} else {
ctx.ModuleErrorf("module %q is not a genrule", depName)
@@ -1358,6 +1370,8 @@
depPaths.CrtBegin = linkFile
case crtEndDepTag:
depPaths.CrtEnd = linkFile
+ case dynamicLinkerDepTag:
+ depPaths.DynamicLinker = linkFile
}
switch depTag {
diff --git a/cmd/extract_linker/main.go b/cmd/extract_linker/main.go
index 3f24ab2..ea0bf4e 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 @@
"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 @@
}
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 @@
}
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 @@
}
fmt.Fprintln(asm)
- sections = append(sections, LinkerSection{
- Name: sectionName,
- Vaddr: baseLoadAddr + prog.Vaddr,
- })
-
load += 1
}
@@ -127,13 +103,10 @@
}
}
- 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 0000000..acce683
--- /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 0000000..0dabbba
--- /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
+}