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Extract the linker and embed it into host bionic binaries

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The linux kernel requires that the ELF interpreter (runtime linker)
that's referenced by PT_INTERP be either an absolute path, or a relative
path from the current working directory. We'd prefer a relative path
from the binary, similarly to how we handle looking up shared libraries,
but that's not supported.

Instead, extract the load sections from the runtime linker ELF binary
and embed them into each host bionic binary, omitting the PT_INTERP
declaration. The kernel will treat it as a static binary, and we'll use
a special entry point (linker_wrapper) to fix up the arguments passed by
the kernel before jumping to the embedded linker. From the linker's
point of view, it looks like the kernel loaded the linker like normal.

Bug: 31559095
Test: Enable host bionic,
      out/soong/host/linux_bionic-x86/nativetest64/libdemangle_test/libdemangle_test
Change-Id: I8d0aea9790b5e86fcc3ea6e2d00cfa33907e2853
This commit is contained in:
Dan Willemsen 2017-09-18 23:19:12 -07:00
parent efb1dd93bf
commit c77a0b3f9c
6 changed files with 307 additions and 12 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

44
Android.bp
View file

@ -310,7 +310,7 @@ toolchain_library {
enabled: false,
target: {
windows: {
enabled: true
enabled: true,
},
},
}
@ -329,3 +329,45 @@ kernel_headers {
name: "device_kernel_headers",
vendor: true,
}
cc_genrule {
name: "host_bionic_linker_asm",
host_supported: true,
device_supported: false,
target: {
linux_bionic: {
enabled: true,
},
linux: {
enabled: false,
},
darwin: {
enabled: false,
},
},
tools: ["extract_linker"],
cmd: "$(location) -s $(out) $(in)",
srcs: [":linker"],
out: ["linker.s"],
}
cc_genrule {
name: "host_bionic_linker_script",
host_supported: true,
device_supported: false,
target: {
linux_bionic: {
enabled: true,
},
linux: {
enabled: false,
},
darwin: {
enabled: false,
},
},
tools: ["extract_linker"],
cmd: "$(location) -T $(out) $(in)",
srcs: [":linker"],
out: ["linker.script"],
}

21
cc/binary.go
View file

@ -15,8 +15,6 @@
package cc
import (
"path/filepath"
"github.com/google/blueprint/proptools"
"android/soong/android"
@ -152,6 +150,10 @@ func (binary *binaryDecorator) linkerDeps(ctx DepsContext, deps Deps) Deps {
[]string{"libc", "libc_nomalloc", "libcompiler_rt"})
deps.LateStaticLibs = append(groupLibs, deps.LateStaticLibs...)
}
if ctx.Os() == android.LinuxBionic && !binary.static() {
deps.LinkerScript = "host_bionic_linker_script"
}
}
if !binary.static() && inList("libc", deps.StaticLibs) {
@ -243,15 +245,7 @@ func (binary *binaryDecorator) linkerFlags(ctx ModuleContext, flags Flags) Flags
case android.Android:
flags.DynamicLinker = "/system/bin/linker"
case android.LinuxBionic:
// The linux kernel expects the linker to be an
// absolute path
path := android.PathForOutput(ctx,
"host", "linux_bionic-x86", "bin", "linker")
if p, err := filepath.Abs(path.String()); err == nil {
flags.DynamicLinker = p
} else {
ctx.ModuleErrorf("can't find path to dynamic linker: %q", err)
}
flags.DynamicLinker = ""
default:
ctx.ModuleErrorf("unknown dynamic linker")
}
@ -304,6 +298,11 @@ func (binary *binaryDecorator) link(ctx ModuleContext,
}
}
if deps.LinkerScript.Valid() {
flags.LdFlags = append(flags.LdFlags, "-Wl,-T,"+deps.LinkerScript.String())
linkerDeps = append(linkerDeps, deps.LinkerScript.Path())
}
if flags.DynamicLinker != "" {
flags.LdFlags = append(flags.LdFlags, " -Wl,-dynamic-linker,"+flags.DynamicLinker)
}

17
cc/cc.go
View file

@ -74,6 +74,7 @@ type Deps struct {
ReexportGeneratedHeaders []string
CrtBegin, CrtEnd string
LinkerScript string
}
type PathDeps struct {
@ -98,6 +99,7 @@ type PathDeps struct {
// Paths to crt*.o files
CrtBegin, CrtEnd android.OptionalPath
LinkerScript android.OptionalPath
}
type Flags struct {
@ -274,6 +276,7 @@ var (
objDepTag = dependencyTag{name: "obj"}
crtBeginDepTag = dependencyTag{name: "crtbegin"}
crtEndDepTag = dependencyTag{name: "crtend"}
linkerScriptDepTag = dependencyTag{name: "linker script"}
reuseObjTag = dependencyTag{name: "reuse objects"}
ndkStubDepTag = dependencyTag{name: "ndk stub", library: true}
ndkLateStubDepTag = dependencyTag{name: "ndk late stub", library: true}
@ -834,6 +837,9 @@ func (c *Module) DepsMutator(actx android.BottomUpMutatorContext) {
if deps.CrtEnd != "" {
actx.AddDependency(c, crtEndDepTag, deps.CrtEnd)
}
if deps.LinkerScript != "" {
actx.AddDependency(c, linkerScriptDepTag, deps.LinkerScript)
}
version := ctx.sdkVersion()
actx.AddVariationDependencies([]blueprint.Variation{
@ -989,6 +995,17 @@ func (c *Module) depsToPaths(ctx android.ModuleContext) PathDeps {
} else {
ctx.ModuleErrorf("module %q is not a genrule", name)
}
case linkerScriptDepTag:
if genRule, ok := m.(genrule.SourceFileGenerator); ok {
files := genRule.GeneratedSourceFiles()
if len(files) == 1 {
depPaths.LinkerScript = 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", name)
}
} else {
ctx.ModuleErrorf("module %q is not a genrule", name)
}
default:
ctx.ModuleErrorf("depends on non-cc module %q", name)
}

20
cmd/extract_linker/Android.bp Normal file
View file

@ -0,0 +1,20 @@
// Copyright 2017 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: "extract_linker",
srcs: ["main.go"],
testSrcs: ["main_test.go"],
}

154
cmd/extract_linker/main.go Normal file
View file

@ -0,0 +1,154 @@
// Copyright 2017 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.
// 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
// in another binary.
package main
import (
"bytes"
"debug/elf"
"flag"
"fmt"
"io"
"io/ioutil"
"log"
"os"
"text/template"
)
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
flag.StringVar(&asmPath, "s", "", "Path to save the assembly file")
flag.StringVar(&scriptPath, "T", "", "Path to save the linker script")
flag.Parse()
f, err := os.Open(flag.Arg(0))
if err != nil {
log.Fatalf("Error opening %q: %v", flag.Arg(0), err)
}
defer f.Close()
ef, err := elf.NewFile(f)
if err != nil {
log.Fatal("Unable to read elf file: %v", err)
}
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
for _, prog := range ef.Progs {
if prog.Type != elf.PT_LOAD {
continue
}
sectionName := fmt.Sprintf(".linker.sect%d", load)
flags := ""
if prog.Flags&elf.PF_W != 0 {
flags += "w"
}
if prog.Flags&elf.PF_X != 0 {
flags += "x"
}
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:")
}
buffer, _ := ioutil.ReadAll(prog.Open())
bytesToAsm(asm, buffer)
// Fill in zeros for any BSS sections. It would be nice to keep
// this as a true BSS, but ld/gold isn't preserving those,
// instead combining the segments with the following segment,
// and BSS only exists at the end of a LOAD segment. The
// linker doesn't use a lot of BSS, so this isn't a huge
// problem.
if prog.Memsz > prog.Filesz {
fmt.Fprintf(asm, ".fill 0x%x, 1, 0\n", prog.Memsz-prog.Filesz)
}
fmt.Fprintln(asm)
sections = append(sections, LinkerSection{
Name: sectionName,
Vaddr: baseLoadAddr + prog.Vaddr,
})
load += 1
}
if asmPath != "" {
if err := ioutil.WriteFile(asmPath, asm.Bytes(), 0777); err != nil {
log.Fatal("Unable to write %q: %v", asmPath, err)
}
}
if scriptPath != "" {
buf := &bytes.Buffer{}
if err := linkerScriptTemplate.Execute(buf, sections); err != nil {
log.Fatal("Failed to create linker script: %v", err)
}
if err := ioutil.WriteFile(scriptPath, buf.Bytes(), 0777); err != nil {
log.Fatal("Unable to write %q: %v", scriptPath, err)
}
}
}
func bytesToAsm(asm io.Writer, buf []byte) {
for i, b := range buf {
if i%64 == 0 {
if i != 0 {
fmt.Fprint(asm, "\n")
}
fmt.Fprint(asm, ".byte ")
} else {
fmt.Fprint(asm, ",")
}
fmt.Fprintf(asm, "%d", b)
}
fmt.Fprintln(asm)
}

63
cmd/extract_linker/main_test.go Normal file
View file

@ -0,0 +1,63 @@
// Copyright 2017 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.
package main
import (
"bytes"
"testing"
)
var bytesToAsmTestCases = []struct {
name string
in []byte
out string
}{
{
name: "empty",
in: []byte{},
out: "\n",
},
{
name: "short",
in: []byte{0x7f, 0x45, 0x4c, 0x46, 0x02, 0x01},
out: ".byte 127,69,76,70,2,1\n",
},
{
name: "multiline",
in: []byte{0x7f, 0x45, 0x4c, 0x46, 0x02, 0x01, 0x01, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x30, 0x00, 0x3e, 0x00, 0x01, 0x00, 0x00, 0x00,
0x50, 0x98, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00,
0x40, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x88, 0xd1, 0x12, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x40, 0x00, 0x38, 0x00,
0x01, 0x00, 0x00, 0x00, 0x40, 0x00, 0x38, 0x00,
0x02, 0x00, 0x00, 0x00, 0x40, 0x00, 0x38, 0x00},
out: ".byte 127,69,76,70,2,1,1,0,0,0,0,0,0,0,0,0,48,0,62,0,1,0,0,0,80,152,2,0,0,0,0,0,64,0,0,0,0,0,0,0,136,209,18,0,0,0,0,0,0,0,0,0,64,0,56,0,1,0,0,0,64,0,56,0\n" +
".byte 2,0,0,0,64,0,56,0\n",
},
}
func TestBytesToAsm(t *testing.T) {
for _, testcase := range bytesToAsmTestCases {
t.Run(testcase.name, func(t *testing.T) {
buf := bytes.Buffer{}
bytesToAsm(&buf, testcase.in)
if buf.String() != testcase.out {
t.Errorf("input: %#v\n want: %q\n got: %q\n", testcase.in, testcase.out, buf.String())
}
})
}
}