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Rework how linux_bionic is built with LLD

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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
This commit is contained in:
Dan Willemsen
2018-10-12 00:24:23 -07:00
parent 9ff34c0ca8
commit a0790e35c7
6 changed files with 295 additions and 68 deletions
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69
cmd/extract_linker/main.go
View File

@@ -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)
}
}
}