Previously, symbols with rust escape sequences (denoted with dollar signs)
weren't demangled if the escape sequence showed up in the middle. This alters
the printing loop to look through the entire string for dollar characters.
This commit switches over the backtrace infrastructure from piggy-backing off
the RUST_LOG environment variable to using the RUST_BACKTRACE environment
variable (logging is now disabled in libstd).
The rust compiler not only outputs symbols in the form that C++ does, but it
also mangle symbols like '&' and '~' to special compiler-defined escape
sequences. For convenience, these symbols are demangled when printing
backtraces.
Whenever a failure happens, if a program is run with
`RUST_LOG=std::rt::backtrace` a backtrace will be printed to the task's stderr
handle. Stack traces are uncondtionally printed on double-failure and
rtabort!().
This ended up having a nontrivial implementation, and here's some highlights of
it:
* We're bundling libbacktrace for everything but OSX and Windows
* We use libgcc_s and its libunwind apis to get a backtrace of instruction
pointers
* On OSX we use dladdr() to go from an instruction pointer to a symbol
* On unix that isn't OSX, we use libbacktrace to get symbols
* Windows, as usual, has an entirely separate implementation
Lots more fun details and comments can be found in the source itself.
Closes#10128
