Android abi和CPU位數

時間 2019-12-05

原文原文鏈接

前言

不知道你們在設置abi的時候，有沒有考慮過這個問題。不一樣的abi之間有什麼區別。32位so又是如何運行在64位機器上的。這個是如何兼容的呢？java

從Zygote提及

相信有了解過系統源碼的同窗都知道這是啥玩意。首先咱們看下init進程在啓動zygote進程是如何作的。以6.0源碼爲例。android

import /init.environ.rc
import /init.usb.rc
import /init.${ro.hardware}.rc
import /init.${ro.zygote}.rc
import /init.trace.rc
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在init.rc文件中，會根據ro.zygote的值去啓動響應支持相應位數的進程。那麼，ro.zygote有幾種取值呢？bash

如圖所示app

zygote32 僅支持32位
zygote64 僅支持64位
zygote32_64 兼容32和64，32位優先
zygote64_32 兼容模式，64位優先

以小米6爲例。屬性值以下。socket

如今看一下init_zygote64_32.rm文件ui

service zygote /system/bin/app_process64 -Xzygote /system/bin --zygote --start-system-server --socket-name=zygote
    class main
    socket zygote stream 660 root system
    onrestart write /sys/android_power/request_state wake
    onrestart write /sys/power/state on
    onrestart restart media
    onrestart restart netd

service zygote_secondary /system/bin/app_process32 -Xzygote /system/bin --zygote --socket-name=zygote_secondary
    class main
    socket zygote_secondary stream 660 root system
    onrestart restart zygote

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能夠很清楚的看到，系統在啓動的時候，會啓動兩個Zygote，一個64位一個32位。spa

Android系統是如何肯定應該是fork 64位仍是32位的呢

有了解過進程啓動的同窗應該看到過以下代碼。rest

synchronized(mLock) {
            return zygoteSendArgsAndGetResult(openZygoteSocketIfNeeded(abi), argsForZygote);
        }
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private ZygoteState openZygoteSocketIfNeeded(String abi) throws ZygoteStartFailedEx {
        Preconditions.checkState(Thread.holdsLock(mLock), "ZygoteProcess lock not held");

        if (primaryZygoteState == null || primaryZygoteState.isClosed()) {
            try {
                primaryZygoteState = ZygoteState.connect(mSocket);
            } catch (IOException ioe) {
                throw new ZygoteStartFailedEx("Error connecting to primary zygote", ioe);
            }
            maybeSetApiBlacklistExemptions(primaryZygoteState, false);
            maybeSetHiddenApiAccessLogSampleRate(primaryZygoteState);
        }
        if (primaryZygoteState.matches(abi)) {
            return primaryZygoteState;
        }

        // The primary zygote didn't match. Try the secondary. if (secondaryZygoteState == null || secondaryZygoteState.isClosed()) { try { secondaryZygoteState = ZygoteState.connect(mSecondarySocket); } catch (IOException ioe) { throw new ZygoteStartFailedEx("Error connecting to secondary zygote", ioe); } maybeSetApiBlacklistExemptions(secondaryZygoteState, false); maybeSetHiddenApiAccessLogSampleRate(secondaryZygoteState); } if (secondaryZygoteState.matches(abi)) { return secondaryZygoteState; } throw new ZygoteStartFailedEx("Unsupported zygote ABI: " + abi); } 複製代碼

會根據abi的值，先去primaryZygoteState匹配而後，再去匹配備選secondaryZygoteState。

那個，ZygoteState中所存儲的abi分類是怎麼來的呢？具體細節不說。這裏的值是經過讀取ro.product.cpu.abilist64，ro.product.cpu.abilist32這兩個屬性得來的。code

#if defined(__LP64__)
static const char ABI_LIST_PROPERTY[] = "ro.product.cpu.abilist64";
static const char ZYGOTE_NICE_NAME[] = "zygote64";
#else
static const char ABI_LIST_PROPERTY[] = "ro.product.cpu.abilist32";
static const char ZYGOTE_NICE_NAME[] = "zygote";
#endif

        if (property_get(ABI_LIST_PROPERTY, prop, NULL) == 0) {
            LOG_ALWAYS_FATAL("app_process: Unable to determine ABI list from property %s.",
                ABI_LIST_PROPERTY);
            return 11;
        }

        String8 abiFlag("--abi-list=");
        abiFlag.append(prop);

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