Preserve x18 while preloading SP-HALs in the zygote.

    }

    native private static void nativePreloadAppProcessHALs();

    native private static void nativePreloadOpenGL();

    private static void preloadOpenGL() {

        String driverPackageName = SystemProperties.get(PROPERTY_GFX_DRIVER);

        if (!SystemProperties.getBoolean(PROPERTY_DISABLE_OPENGL_PRELOADING, false) &&

                (driverPackageName == null || driverPackageName.isEmpty())) {

            EGL14.eglGetDisplay(EGL14.EGL_DEFAULT_DISPLAY);

            nativePreloadOpenGL();

        }

    }

#define LOG_TAG "Zygote"

#include <EGL/egl.h>

#include <ui/GraphicBufferMapper.h>

#include "core_jni_helpers.h"

namespace {

// Shadow call stack (SCS) is a security mitigation that uses a separate stack

// (the SCS) for return addresses. In versions of Android newer than P, the

// compiler cooperates with the system to ensure that the SCS address is always

// stored in register x18, as long as the app was compiled with a new enough

// compiler and does not use features that rely on SP-HALs (this restriction is

// because the SP-HALs might not preserve x18 due to potentially having been

// compiled with an old compiler as a consequence of Treble; it generally means

// that the app must be a system app without a UI). This struct is used to

// temporarily store the address on the stack while preloading the SP-HALs, so

// that such apps can use the same zygote as everything else.

struct ScopedSCSExit {

#ifdef __aarch64__

    void* scs;

    ScopedSCSExit() {

        __asm__ __volatile__("str x18, [%0]" ::"r"(&scs));

    }

    ~ScopedSCSExit() {

        __asm__ __volatile__("ldr x18, [%0]; str xzr, [%0]" ::"r"(&scs));

    }

#else

    // Silence unused variable warnings in non-SCS builds.

    ScopedSCSExit() {}

    ~ScopedSCSExit() {}

#endif

};

void android_internal_os_ZygoteInit_nativePreloadAppProcessHALs(JNIEnv* env, jclass) {

    ScopedSCSExit x;

    android::GraphicBufferMapper::preloadHal();

    // Add preloading here for other HALs that are (a) always passthrough, and

    // (b) loaded by most app processes.

}

void android_internal_os_ZygoteInit_nativePreloadOpenGL(JNIEnv* env, jclass) {

    ScopedSCSExit x;

    eglGetDisplay(EGL_DEFAULT_DISPLAY);

}

const JNINativeMethod gMethods[] = {

    { "nativePreloadAppProcessHALs", "()V",

      (void*)android_internal_os_ZygoteInit_nativePreloadAppProcessHALs },

    { "nativePreloadOpenGL", "()V",

      (void*)android_internal_os_ZygoteInit_nativePreloadOpenGL },

};

}  // anonymous namespace