This change implements the following property:
Any 2**N aligned memory region on size 2**N contains no more than one DSO.
The value N can be configured, with 16 or 18 looking like a good choice.
Additionally, DSOs are loaded at random page-aligned address inside these large
regions.
This change has dual purpose:
1. Larger values of N allow a lot more compact CFI shadow implementation.
See change I14dfea630de468eb5620e7f55f92b1397ba06217.
For example, CFI shadow for the system_server process has the following size (RSS, KB):
152 for N = 12, 32 for N = 16, 16 for N = 18.
2. Extra randomization is good for security.
This change does not result in extra RAM usage, because everything is still page-aligned.
It does result in a bit more VM fragmentation because of the gaps between shared libraries.
As it turns out, this fragmentation is barely noticeable because the kernel creates new mapping
at the highest possible address, and we do enough small mappings to almost completely fill the
gaps (ex. in the Zygote the gaps are filled with .ttf file mappings and thread stacks).
I've measured VM fragmentation as the sum of all VM gaps (unmapped regions) that are larger
than 1MB according to /proc/$PID/maps. On aosp_angler-userdebug, the numbers are (in GB):
| N = 12 | N = 18
system_server | 521.9 | 521.1
zygote64 | 522.1 | 521.3
zygote32 | 2.55 | 2.55
mediaserver | 4.00 | 4.00
Change-Id: Ia6df840dd409c82837efd1f263be420d9723c84a
The BIONIC_ROUND_UP_POWER_OF_2 macro did not have parentheses around
the whole expression. This lead to the wrong value being computed when
used as part of a mathematical expression such as this:
value = BIONIC_ROUND_UP_POWER_OF_2(value) - 1;
This only happens on 64 bit abis.
Change-Id: I6f8afbdaf16fe64a88fa0246d074b3534c9159c1
Make the definition of DISALLOW_COPY_AND_ASSIGN conditional. This is
so that the projects that include libnativehelper and bionic macros
do not have to be careful in which order those projects are included.
Bug: 18334516
Change-Id: Ib12a2c2b7ad2e360edcf3b26cb1be626540fadc1
Enable the -std=gnu++11 flag for libstdc++ static and
dynamic libs.
ScopeGuard uses DISABLE_ macros instead of '= delete';
Change-Id: I07e21b306f95fffd49345f7fa136cfdac61e0225
There were two bugs here:
- For 64 bit values, this did not properly round up.
- The macro rounded to the power of 2 less than value, not to the power
of 2 greater than value.
Change-Id: If8cb41536a9d2f5c1bc213676f1e67a7903a36b0
