We shouldn't use O_EXCL, since we need to overwrite previous entry PIDs
if they happen to exist. The kernel ensures that PIDs don't overlap, but
in some kernel configurations PIDs are aggressively reused, resulting
in O_EXCL quickly hitting an issue when writing stale files.
Additionally O_DIRECT, this doesn't allow us to write to files, so all
write functions were failing.
Additionally use O_APPEND, we are only ever appending, so let the kernel
know.
Additionally use O_TRUNC, in the case that a stale perf file exists,
this will immediately truncate the file to zero.
When a process is in the process of forking and getting ready for
execve, it is common practice to do a `close_range` or close loop to
close all file descriptors before the execve.
This is a security/sanitization feature to ensure that FDs aren't leaked
to the child process. While it is more reliable to have these FDs opened
with O_CLOEXEC, people get it wrong all the time so this feature has
been put in place. Both python and glibc wrappers for launching
applications do this.
The problem with this for FEX is that we were using a FILE handle for
emitting JIT symbols to the perf file. When the underlying FD is ripped
out from under the FILE handle, it throws an assert that we can't
recover from.
Switching to a raw FD and checking to ensure the FD is still open on
writes means that we can safely stop JIT symbol logging when a process
is closing FDs under us.
Fixes a crash in Steam early startup where a python script is run for
checking if packages are installed.
In most cases we aren't using JIT symbols but still creating the perf
map file.
Early check if we should generate the file or not, this way we stop
polluting the /tmp folder.
Brings along a bunch of enhancements and ensures we always build against
the latest version.
Also fixes up a few issues that arose due to changes in fmt
This lets us have JITsymbols grouped by library.
Useful for determining where to thunk.
Sadly perf doesn't have an option to deduplicate regions by name, so
some external tooling is necessary to make it look nice.
Ryan Houdek