tree 8a3ce9535e93d57f03feaf036543acf330d48813
parent 24f9dab40787b754482944f8af90f22d393346c0
author Ryan Savitski <rsavitski@google.com> 1644241820 +0000
committer Ryan Savitski <rsavitski@google.com> 1644597084 +0000

profiling: override dumpability while opening /proc/self/mem,maps

For the perf profiling signal handler to succeed in opening
/proc/self/mem, the process needs to be marked as dumpable in posix
terms. This patch addresses a scenario since Android S where the process
is considered profileable, but is not dumpable on "user" builds. The
solution is to mark the process as dumpable while opening the procfs
descriptors, restoring the original value afterwards. This is the same
approach as the heapprofd heap profiler, which performs the override
within the loaded client library [1].

The particular scenario being addressed is:
* user build
* app does not explicitly opt into being profiled by shell
* app does not explicitly opt out of all profiling
In this case, the app is considered profileable by the platform (but NOT
shell). Therefore ActivityThread marks the process as profileable [2],
but the zygote keeps the process as undumpable as it considers the
profileability from the shell domain [3]. We could change the logic in
the zygote to leave such processes in the dumpable state, but the
override within the signal handler is considered to be more contained as
the dumpability is only needed temporarily.

This override would also apply for any non-dumpable native services that
are signalled for profiling, which is also desireable for profiling
coverage.

This change does not elide any of the existing profileability
checks by the signal handler's preamble and the profiler itself.

[1]
https://cs.android.com/android/platform/superproject/+/master:external/perfetto/src/profiling/memory/client.cc;l=184;drc=78cd82ba31233ce810618e07d349fd34efdb861d
[2]
https://cs.android.com/android/platform/superproject/+/master:frameworks/base/core/java/android/app/ActivityThread.java;l=6610;drc=de9cf3392d7872c2bee69b65a614e77bb166b26e
[3]
https://cs.android.com/android/platform/superproject/+/master:frameworks/base/core/jni/com_android_internal_os_Zygote.cpp;l=1680;drc=master

Tested: clock app on barbet-user succeeds in opening the procfs
descriptors within the signal handler.
Tested: systemwide profiling on sargo-userdebug works as before.
Bug: 196810669
BYPASS_INCLUSIVE_LANGUAGE_REASON=referencing the name of a cmdline utility
Change-Id: Id621d4312418ff0736c97065e9ee577ff67f40da