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| <head> |
| <title>Using Strace</title> |
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| |
| <p><a href="https://strace.io">Strace</a> enables you to see the system calls a |
| process makes and what those system calls return. A typical process makes a lot |
| of system calls, so you'll want to review the |
| <a href="http://man7.org/linux/man-pages/man1/strace.1.html">strace man page</a> |
| to learn how to collect only data you're actually interested in.</p> |
| |
| <h2 id=build-strace>Building strace</h2> |
| |
| <p>To build strace, run the following: |
| <pre class="devsite-terminal devsite-click-to-copy"> |
| mmma -j6 external/strace |
| </pre> |
| |
| <h2 id=attach-strace>Attaching to a running process</h2> |
| |
| <p>The simplest and most common use case for strace is to attach it to a running |
| process, which you can do with:</p> |
| <pre class="devsite-terminal devsite-click-to-copy"> |
| adb shell strace -f -p PID |
| </pre> |
| <p>The <code>-f</code> flag tells strace to attach to all the threads in the |
| process, plus any new threads spawned later.</p> |
| |
| <h2 id=app-strace>Using on an application</h2> |
| <p>To use strace on an application:</p> |
| |
| <ol> |
| <li>Set up a directory for strace logs: |
| <pre class="devsite-click-to-copy"> |
| <code class="devsite-terminal">adb shell setenforce 0</code> |
| <code class="devsite-terminal">adb shell mkdir /data/local/tmp/strace</code> |
| <code class="devsite-terminal">adb shell chmod 777 /data/local/tmp/strace</code> |
| </pre> |
| </li> |
| |
| <li>Choose the process to trace before launching it: |
| <pre class="devsite-terminal devsite-click-to-copy"> |
| adb shell setprop wrap.com.google.android.browser "logwrapper strace -f -o /data/local/tmp/strace/strace.com.google.android.browser.txt" |
| </pre> |
| </li> |
| <li>Launch the process normally.</li> |
| </ol> |
| |
| <h2 id=zygote-systrace>Using on the zygote</h2> |
| <p>To use strace on the zygote, fix the relevant <code>init.rc</code> zygote |
| line (requires <code>adb shell setenforce 0</code>): |
| </p> |
| |
| <pre class="devsite-click-to-copy"> |
| <code class="devsite-terminal">cd system/core/</code> |
| <code class="devsite-terminal">patch -p1 <<EOF |
| --- a/rootdir/init.zygote32.rc |
| +++ b/rootdir/init.zygote32.rc |
| @@ -1,4 +1,4 @@ |
| -service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server |
| +service zygote /system/xbin/strace -o /data/local/tmp/zygote.strace /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server |
| class main |
| socket zygote stream 660 root system |
| onrestart write /sys/android_power/request_state wake |
| EOF</code> |
| </pre> |
| |
| <h2 id=get-logs-boot>Getting strace logs during Android boot</h2> |
| |
| <p>To get strace logs during Android boot, make the following changes:</p> |
| |
| <ul> |
| <li>Since the process name changes from <code>zygote</code> to |
| <code>strace</code>, the given service may fail to start due to the missing |
| SELinux <code>file_context</code> for <code>strace</code>. The solution is to |
| add a new line for strace in <code>system/sepolicy/private/file_contexts</code> |
| and copy the original file context over. Example: |
| <pre class="devsite-click-to-copy"> |
| /dev/socket/zygote u:object_r:zygote_socket:s0 |
| + /system/xbin/strace u:object_r:zygote_socket:s0 |
| </pre> |
| </li> |
| |
| <li>Add kernel command, then boot the device in SELinux permissive mode. You can |
| do this by adding <code>androidboot.selinux=permissive</code>to |
| <code>BOARD_KERNEL_CMDLINE</code>. (This variable becomes read-only in |
| <code>build/core/Makefile</code> but is always available under |
| <code>/device/*/BoardConfig</code>.) |
| |
| <br> |
| <br>Example for the Pixel (sailfish) device in |
| <code>/device/google/marlin/sailfish/BoardConfig.mk</code>: |
| <pre class="devsite-click-to-copy"> |
| - BOARD_KERNEL_CMDLINE := .... androidboot.hardware=sailfish ... |
| +BOARD_KERNEL_CMDLINE := .... androidboot.hardware=sailfish ... androidboot.selinux=permissive |
| </pre> |
| After making the change, build and flash the boot image and the device will boot |
| in permissive mode. |
| </li> |
| </ul> |
| |
| </body> |
| </html> |
