tree 483cba96eb8cbc8e06a2ef8651f66d208626e30b
parent 2e40c1c2e9c8cfc2d41a8960247bfa48e2500889
author Alex Light <allight@google.com> 1517592331 -0800
committer Alex Light <allight@google.com> 1517598278 -0800

Change ClassFileLoadHook to lazily compute dex file

Creating a dex file from the quickened or compact-dex'd internal
format for calling the JVMTI ClassFileLoadHook is quite expensive.
This meant that agents could not generally listen for this event
without causing unacceptable performance problems.

Since agents will generally not touch the buffer, needing to
instrument only a handful of classes we will fix this problem by doing
the de-quickening lazily. This is done by mmaping an empty buffer with
PROT_NONE and then filling it in when the program has a SEGV in the
appropriate address range. This should improve the performance of any
agent that listens for the ClassFileLoadHook but does not commonly do
anything to the buffer.

This does have the disadvantage that we can no longer ensure that the
buffer size we pass down in class_data_len might no longer be fully
accurate. Some agents that assert that class_data_len is exactly the
same as the dex-file will need to be updated.

Bug: 72402467
Bug: 72064989
Test: ./test.py --host -j50
Test: ./test.py --host --redefine-stress -j50

Change-Id: I39354837f1417ae10a57c5b42cbb4f38f8a563dc