cmd/link: detect glibc vs musl ldso at link time

Doing the test at link time lets us distribute one Linux toolchain
that works on both glibc-based and musl-based Linux systems.
The old way built a toolchain that only ran on one or the other.

Fixes #54197.

Change-Id: Iaae8c274c78e1091eee828a720b49646be9bfffe
Reviewed-on: https://go-review.googlesource.com/c/go/+/420774
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>

src/cmd/link/internal/amd64/obj.go

@@ -65,6 +65,7 @@ func Init() (*sys.Arch, ld.Arch) {
 		TLSIEtoLE:        tlsIEtoLE,
 
 		Linuxdynld:     "/lib64/ld-linux-x86-64.so.2",
+		LinuxdynldMusl: "/lib/ld-musl-x84_64.so.1",
 		Freebsddynld:   "/libexec/ld-elf.so.1",
 		Openbsddynld:   "/usr/libexec/ld.so",
 		Netbsddynld:    "/libexec/ld.elf_so",

src/cmd/link/internal/arm/obj.go

@@ -63,6 +63,7 @@ func Init() (*sys.Arch, ld.Arch) {
 		PEreloc1:         pereloc1,
 
 		Linuxdynld:     "/lib/ld-linux.so.3", // 2 for OABI, 3 for EABI
+		LinuxdynldMusl: "/lib/ld-musl-arm.so.1",
 		Freebsddynld:   "/usr/libexec/ld-elf.so.1",
 		Openbsddynld:   "/usr/libexec/ld.so",
 		Netbsddynld:    "/libexec/ld.elf_so",

src/cmd/link/internal/arm64/obj.go

@@ -62,8 +62,9 @@ func Init() (*sys.Arch, ld.Arch) {
 		PEreloc1:         pereloc1,
 		Trampoline:       trampoline,
 
-		Androiddynld: "/system/bin/linker64",
-		Linuxdynld:   "/lib/ld-linux-aarch64.so.1",
+		Androiddynld:   "/system/bin/linker64",
+		Linuxdynld:     "/lib/ld-linux-aarch64.so.1",
+		LinuxdynldMusl: "/lib/ld-musl-aarch64.so.1",
 
 		Freebsddynld:   "/usr/libexec/ld-elf.so.1",
 		Openbsddynld:   "/usr/libexec/ld.so",

src/cmd/link/internal/ld/elf.go

@@ -15,6 +15,7 @@ import (
 	"encoding/hex"
 	"fmt"
 	"internal/buildcfg"
+	"os"
 	"path/filepath"
 	"runtime"
 	"sort"
@@ -1782,6 +1783,16 @@ func asmbElf(ctxt *Link) {
 					}
 				} else {
 					interpreter = thearch.Linuxdynld
+					// If interpreter does not exist, try musl instead.
+					// This lets the same cmd/link binary work on
+					// both glibc-based and musl-based systems.
+					if _, err := os.Stat(interpreter); err != nil {
+						if musl := thearch.LinuxdynldMusl; musl != "" {
+							if _, err := os.Stat(musl); err == nil {
+								interpreter = musl
+							}
+						}
+					}
 				}
 
 			case objabi.Hfreebsd:

src/cmd/link/internal/ld/lib.go

@@ -183,6 +183,7 @@ type Arch struct {
 
 	Androiddynld   string
 	Linuxdynld     string
+	LinuxdynldMusl string
 	Freebsddynld   string
 	Netbsddynld    string
 	Openbsddynld   string

src/cmd/link/internal/loong64/obj.go

@@ -31,6 +31,7 @@ func Init() (*sys.Arch, ld.Arch) {
 		Gentext:          gentext,
 
 		Linuxdynld:     "/lib64/ld.so.1",
+		LinuxdynldMusl: "/lib64/ld-musl-loongarch.so.1",
 		Freebsddynld:   "XXX",
 		Openbsddynld:   "XXX",
 		Netbsddynld:    "XXX",

src/cmd/link/internal/mips/obj.go

@@ -39,8 +39,10 @@ import (
 
 func Init() (*sys.Arch, ld.Arch) {
 	arch := sys.ArchMIPS
+	musl := "/lib/ld-musl-mips.so.1"
 	if buildcfg.GOARCH == "mipsle" {
 		arch = sys.ArchMIPSLE
+		musl = "/lib/ld-musl-mipsel.so.1"
 	}
 
 	theArch := ld.Arch{
@@ -60,7 +62,8 @@ func Init() (*sys.Arch, ld.Arch) {
 		Gentext:          gentext,
 		Machoreloc1:      machoreloc1,
 
-		Linuxdynld: "/lib/ld.so.1",
+		Linuxdynld:     "/lib/ld.so.1",
+		LinuxdynldMusl: musl,
 
 		Freebsddynld:   "XXX",
 		Openbsddynld:   "XXX",

src/cmd/link/internal/mips64/obj.go

@@ -39,8 +39,10 @@ import (
 
 func Init() (*sys.Arch, ld.Arch) {
 	arch := sys.ArchMIPS64
+	musl := "/lib/ld-musl-mips64.so.1"
 	if buildcfg.GOARCH == "mips64le" {
 		arch = sys.ArchMIPS64LE
+		musl = "/lib/ld-musl-mips64el.so.1"
 	}
 
 	theArch := ld.Arch{
@@ -60,6 +62,7 @@ func Init() (*sys.Arch, ld.Arch) {
 		Machoreloc1:      machoreloc1,
 
 		Linuxdynld:     "/lib64/ld64.so.1",
+		LinuxdynldMusl: musl,
 		Freebsddynld:   "XXX",
 		Openbsddynld:   "/usr/libexec/ld.so",
 		Netbsddynld:    "XXX",

src/cmd/link/internal/ppc64/obj.go

@@ -40,10 +40,12 @@ import (
 func Init() (*sys.Arch, ld.Arch) {
 	arch := sys.ArchPPC64LE
 	dynld := "/lib64/ld64.so.2"
+	musl := "/lib/ld-musl-powerpc64le.so.1"
 
 	if buildcfg.GOARCH == "ppc64" {
 		arch = sys.ArchPPC64
 		dynld = "/lib64/ld64.so.1"
+		musl = "/lib/ld-musl-powerpc64.so.1"
 	}
 
 	theArch := ld.Arch{
@@ -68,6 +70,8 @@ func Init() (*sys.Arch, ld.Arch) {
 		Xcoffreloc1:      xcoffreloc1,
 
 		Linuxdynld:     dynld,
+		LinuxdynldMusl: musl,
+
 		Freebsddynld:   "XXX",
 		Openbsddynld:   "XXX",
 		Netbsddynld:    "XXX",

src/cmd/link/internal/s390x/obj.go

@@ -56,7 +56,8 @@ func Init() (*sys.Arch, ld.Arch) {
 		Gentext:          gentext,
 		Machoreloc1:      machoreloc1,
 
-		Linuxdynld: "/lib64/ld64.so.1",
+		Linuxdynld:     "/lib64/ld64.so.1",
+		LinuxdynldMusl: "/lib/ld-musl-s390x.so.1",
 
 		// not relevant for s390x
 		Freebsddynld:   "XXX",

src/cmd/link/internal/x86/obj.go

@@ -61,11 +61,12 @@ func Init() (*sys.Arch, ld.Arch) {
 		Machoreloc1:      machoreloc1,
 		PEreloc1:         pereloc1,
 
-		Linuxdynld:   "/lib/ld-linux.so.2",
-		Freebsddynld: "/usr/libexec/ld-elf.so.1",
-		Openbsddynld: "/usr/libexec/ld.so",
-		Netbsddynld:  "/usr/libexec/ld.elf_so",
-		Solarisdynld: "/lib/ld.so.1",
+		Linuxdynld:     "/lib/ld-linux.so.2",
+		LinuxdynldMusl: "/lib/ld-musl-i386.so.1",
+		Freebsddynld:   "/usr/libexec/ld-elf.so.1",
+		Openbsddynld:   "/usr/libexec/ld.so",
+		Netbsddynld:    "/usr/libexec/ld.elf_so",
+		Solarisdynld:   "/lib/ld.so.1",
 	}
 
 	return arch, theArch

src/make.bash

@@ -133,15 +133,6 @@ if [ "$(uname -s)" = "GNU/kFreeBSD" ]; then
 	export CGO_ENABLED=0
 fi
 
-# Test which linker/loader our system is using, if GO_LDSO is not set.
-if [ -z "$GO_LDSO" ] && type readelf >/dev/null 2>&1; then
-	if echo "int main() { return 0; }" | ${CC:-cc} -o ./test-musl-ldso -x c - >/dev/null 2>&1; then
-		LDSO=$(readelf -l ./test-musl-ldso | grep 'interpreter:' | sed -e 's/^.*interpreter: \(.*\)[]]/\1/') >/dev/null 2>&1
-		[ -z "$LDSO" ] || export GO_LDSO="$LDSO"
-		rm -f ./test-musl-ldso
-	fi
-fi
-
 # Clean old generated file that will cause problems in the build.
 rm -f ./runtime/runtime_defs.go