The backtracing code will warn you if you attempt to forcibly enable
backtracing for a privileged executable. This is apparently upsetting
the Driver/filelists.swift test.
Since we want to force it on for tests, so that we will definitely get
backtraces, add an option to suppress warning messages, and turn that
on for tests as well.
rdar://144497613
We should harden the output path setting so that it can't be used
as part of an exploit to get a crashing process to overwrite a
file at an attacker-controller path, or to divert the crash report
to `/dev/null` to hide their tracks or other such undesirable
activity.
Take a copy of the setting at start-up and write-protect it to
prevent attackers overwriting it.
Note that we already protect against attempts to trigger the
backtracer from privileged programs (both on Darwin and Linux);
this is really a belt and braces measure to make life harder for
attackers.
rdar://136977833
Add the ability to specify a filename or directory name as the output-to
setting in `SWIFT_BACKTRACE`. If the option is set to a directory name,
generate a unique filename in that directory using the process name,
process ID and timestamp.
rdar://136977833
Rather than just on or off, I've changed it to allow "off", "fast",
or "full". "fast" means that we'll do symbol lookup, but we won't
try to find inline frames and we won't run line number programs
(those are the things that are taking considerable time in some
cases).
rdar://122302117
Symbolication can take some time, depending on the binaries involved.
In certain contexts it's better for the backtrace to finish quickly,
and then symbolication could be done offline.
rdar://122302117
We shouldn't try to erase the message when in non-color mode; mostly
that's intended for redirected output scenarios anyway, and in that case
we don't really want garbage in the output.
Also, improve the failure messages when the backtracer itself goes
wrong or can't be executed.
Finally, change the behaviour slightly so that *if* we're explicitly
enabled, *and* the backtracer path wasn't explicitly specified, *and*
we can't find the backtracer, we print a warning on start-up. We
don't do that in any other case because we don't want spurious warnings
everywhere.
rdar://118055527
When we crash, emit a message straight away that says we're working
on a backtrace. If starting the backtracer fails, report that also.
Finally, add a duration to the messages output by the backtracer, so
that we can see how long it took.
rdar://118055527
