There are two parts to this patch; both affect only Linux:
1. The GMP sandbox policy is adjusted to allow certain syscalls used in
shared memory creation (ftruncate and fallocate). However, the file
broker is not used; the process still has no access to files in /dev/shm.
2. The profiler is not initialized for GMP processes unless memfd_create
is available (so the process can create shared memory to send
profiling data back, without filesystem access), or the GMP sandbox
is disabled (either at runtime or build time).
As of this patch, profiling GMP processes on Linux should succeed on
distros with kernel >=3.17 (Oct. 2014), but native stack frames won't
have symbols (and may be incorrectly unwound, not that it matters much
without symbols); see the bug for more info. Pseudo-stack frames and
markers should work, however.
Differential Revision: https://phabricator.services.mozilla.com/D148470
4db39d8f8d