os: don't use pidfd on Android < 12

In Android version 11 and earlier, pidfd-related system calls are not
allowed by the seccomp policy, which causes crashes due to SIGSYS signals.

Fixes #69065

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

@@ -44,6 +44,7 @@ import (
 	"encoding/binary"
 	"fmt"
 	"internal/abi"
+	"internal/buildcfg"
 	"log"
 	"math/rand"
 	"os"
@@ -260,8 +261,8 @@ func (st *relocSymState) relocsym(s loader.Sym, P []byte) {
 		}
 
 		// We need to be able to reference dynimport symbols when linking against
-		// shared libraries, and AIX, Darwin, OpenBSD and Solaris always need it.
-		if !target.IsAIX() && !target.IsDarwin() && !target.IsSolaris() && !target.IsOpenbsd() && rs != 0 && rst == sym.SDYNIMPORT && !target.IsDynlinkingGo() && !ldr.AttrSubSymbol(rs) {
+		// shared libraries, and AIX, Darwin, OpenBSD, Android and Solaris always need it.
+		if !target.IsAIX() && !target.IsDarwin() && !target.IsSolaris() && !target.IsOpenbsd() && buildcfg.GOOS != "android" && rs != 0 && rst == sym.SDYNIMPORT && !target.IsDynlinkingGo() && !ldr.AttrSubSymbol(rs) {
 			if !(target.IsPPC64() && target.IsExternal() && ldr.SymName(rs) == ".TOC.") {
 				st.err.Errorf(s, "unhandled relocation for %s (type %d (%s) rtype %d (%s))", ldr.SymName(rs), rst, rst, rt, sym.RelocName(target.Arch, rt))
 			}

src/os/pidfd_linux.go

@@ -14,6 +14,7 @@ package os
 import (
 	"errors"
 	"internal/syscall/unix"
+	"runtime"
 	"sync"
 	"syscall"
 	"unsafe"
@@ -147,6 +148,11 @@ var checkPidfdOnce = sync.OnceValue(checkPidfd)
 // execution environment in which the above system calls are restricted by
 // seccomp or a similar technology.
 func checkPidfd() error {
+	// In Android version < 12, pidfd_open and pidfd_send_signal are not allowed by seccomp.
+	if runtime.GOOS == "android" && androidVersion() < 12 {
+		return NewSyscallError("pidfd_send_signal", syscall.ENOSYS)
+	}
+
 	// Get a pidfd of the current process (opening of "/proc/self" won't
 	// work for waitid).
 	fd, err := unix.PidFDOpen(syscall.Getpid(), 0)

src/os/version_android.go

@@ -0,0 +1,10 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os
+
+import _ "unsafe" // for go:linkname
+
+//go:linkname androidVersion runtime.androidVersion
+func androidVersion() int

src/os/version_other.go

@@ -0,0 +1,11 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !android
+
+package os
+
+func androidVersion() int {
+	return 0
+}

src/runtime/os_android.go

@@ -4,7 +4,25 @@
 
 package runtime
 
-import _ "unsafe" // for go:cgo_export_static and go:cgo_export_dynamic
+import (
+	"unsafe"
+)
+
+//go:linkname androidVersion runtime.androidVersion
+func androidVersion() int {
+	const PROP_VALUE_MAX = 92
+	var value [PROP_VALUE_MAX]byte
+	name := []byte("ro.build.version.release\x00")
+	length := __system_property_get(&name[0], &value[0])
+	for i := int32(0); i < length; i++ {
+		if value[i] < '0' || value[i] > '9' {
+			length = i
+			break
+		}
+	}
+	version, _ := atoi(unsafe.String(&value[0], length))
+	return version
+}
 
 // Export the main function.
 //

src/runtime/sys_android.go

@@ -0,0 +1,28 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package runtime
+
+import (
+	"internal/abi"
+	"unsafe"
+)
+
+// The *_trampoline functions convert from the Go calling convention to the C calling convention
+// and then call the underlying libc function. These are defined in sys_android_$ARCH.s.
+
+//go:nosplit
+//go:cgo_unsafe_args
+func __system_property_get(name *byte, value *byte) int32 {
+	ret := libcCall(unsafe.Pointer(abi.FuncPCABI0(__system_property_get_trampoline)), unsafe.Pointer(&name))
+	KeepAlive(name)
+	KeepAlive(value)
+	return ret
+}
+func __system_property_get_trampoline()
+
+// Tell the linker that the libc_* functions are to be found
+// in a system library, with the libc_ prefix missing.
+
+//go:cgo_import_dynamic libc___system_property_get __system_property_get "libc.so"

src/runtime/sys_android_386.s

@@ -0,0 +1,27 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#include "go_asm.h"
+#include "textflag.h"
+
+// These trampolines help convert from Go calling convention to C calling convention.
+// They should be called with asmcgocall - note that while asmcgocall does
+// stack alignment, creation of a frame undoes it again.
+// A pointer to the arguments is passed on the stack.
+// A single int32 result is returned in AX.
+// (For more results, make an args/results structure.)
+TEXT runtime·__system_property_get_trampoline(SB),NOSPLIT,$0
+	PUSHL	BP
+	MOVL	SP, BP
+	SUBL	$8, SP
+	MOVL	16(SP), DX		// pointer to args
+	MOVL	0(DX), AX
+	MOVL	4(DX), DX
+	MOVL	AX, 0(SP)		// arg 1 - name
+	MOVL	DX, 4(SP)		// arg 2 - value
+	MOVL	$_GLOBAL_OFFSET_TABLE_(SB), BX
+	CALL	libc___system_property_get(SB)
+	MOVL	BP, SP
+	POPL	BP
+	RET

src/runtime/sys_android_amd64.s

@@ -0,0 +1,17 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#include "go_asm.h"
+#include "textflag.h"
+
+// These trampolines help convert from Go calling convention to C calling convention.
+// They should be called with asmcgocall.
+// A pointer to the arguments is passed in DI.
+// A single int32 result is returned in AX.
+// (For more results, make an args/results structure.)
+TEXT runtime·__system_property_get_trampoline(SB),NOSPLIT,$0
+	MOVQ	8(DI), SI		// arg 2 - value
+	MOVQ	0(DI), DI		// arg 1 - name
+	CALL	libc___system_property_get(SB)
+	RET

src/runtime/sys_android_arm.s

@@ -0,0 +1,21 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#include "go_asm.h"
+#include "textflag.h"
+
+// These trampolines help convert from Go calling convention to C calling convention.
+// They should be called with asmcgocall - note that while asmcgocall does
+// stack alignment, creation of a frame undoes it again.
+// A pointer to the arguments is passed in R0.
+// A single int32 result is returned in R0.
+// (For more results, make an args/results structure.)
+TEXT runtime·__system_property_get_trampoline(SB),NOSPLIT,$0
+	MOVW	R13, R9
+	BIC	$0x7, R13		// align for ELF ABI
+	MOVW	4(R0), R1		// arg 2 - value
+	MOVW	0(R0), R0		// arg 1 - name
+	CALL	libc___system_property_get(SB)
+	MOVW	R9, R13
+	RET

src/runtime/sys_android_arm64.s

@@ -0,0 +1,17 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#include "go_asm.h"
+#include "textflag.h"
+
+// These trampolines help convert from Go calling convention to C calling convention.
+// They should be called with asmcgocall.
+// A pointer to the arguments is passed in R0.
+// A single int32 result is returned in R0.
+// (For more results, make an args/results structure.)
+TEXT runtime·__system_property_get_trampoline(SB),NOSPLIT,$0
+	MOVD	8(R0), R1		// arg 2 - value
+	MOVD	0(R0), R0		// arg 1 - name
+	CALL	libc___system_property_get(SB)
+	RET

src/runtime/sys_libc.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build darwin || (openbsd && !mips64)
+//go:build darwin || (openbsd && !mips64) || android
 
 package runtime