tree f75ac7fa624eb3e092f7179df8094a6f9e9290c9
parent 3936985e75eace1adeeb8d64d4c98e737318d284
author Peter Collingbourne <pcc@google.com> 1599687423 -0700
committer Peter Collingbourne <pcc@google.com> 1599771324 -0700

Implement a new mechanism to let Scudo access the TLS slot

An upcoming change to Scudo will change how we use the TLS slot
in tsd_shared.h, which will be a little easier to deal with if
we can remove the code path that calls pthread_getspecific and
pthread_setspecific. The only known user of this code path is Fuchsia.

We can't eliminate this code path by making Fuchsia use ELF TLS
because although Fuchsia supports ELF TLS, it is not supported within
libc itself. To address this, Roland McGrath on the Fuchsia team has
proposed that Scudo will optionally call a platform-provided function
to access a TLS slot reserved for Scudo. Android also has a reserved
TLS slot, but the code that accesses the TLS slot lives in Scudo.

We can eliminate some complexity and duplicated code by having Android
implement the same mechanism that was proposed for Fuchsia, which is
what this change does. A separate change to Scudo will make use of it.

Bug: 163630045
Change-Id: I4678105c9c47a23feb5a5e80a314416de4556d9c