RUST_BACKTRACE=1 should be set

[omo]

The error message of rustc internal compiler errors asks this.

It'd be great if we can post a reproduction code on play.rust-lang.org and
the compiler developer sees the live diagnose information there.

[ghost]

Depends on: rust-lang/rust#29293

[jonas-schievink]

Depends on: rust-lang/rust#29293

That only happens when rustc is compiled with debuginfo btw, so it shouldn't affect playpen

[respeccing]

That only happens when rustc is compiled with debuginfo btw, so it shouldn't affect playpen

You're right - I misunderstood what Mode: Debug means in playpen: "debug assertions on"(--enable-debug-assertions) is not the same as debugging info on(--enable-debuginfo).

[respeccing]

EDIT5: NEVERMIND what I said below, it's easier than I thought!

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tl;dr: must modify playpen.c to accept env. var(s) from arguments. OR pass a command like this to playpen bash -c 'export RUST_BACKTRACE=1;set|grep -i rust'

Looks like an env var could only be set in playpen.c: https://github.com/thestinger/playpen/blob/f8becccff56827c1d9ed70f0edc9470bf408bb86/playpen.c#L774-L780

Perhaps if rustc had an arg that would do the same thing as the RUST_BACKTRACE env var, that would be preferable ? (and while at it it would be even better if this arg could override the env var - I found myself in need of forcing that which is why I made a variant as RUST_BACKTRACE=disabled to mean the same as the env var being unset.)

EDIT: actually, I just realized an error in my thinking... it's the resulting binary which needs that arg, not rustc! That is, to emulate the env var being set. Although rustc could, in theory, permanently set that in the resulting binary. But having that binary accept an arg is out of the question /unacceptable, imho.
EDIT6: actually both rustc (while compiling) and the output binary(./out) might need RUST_BACKTRACE to be set, (so not just ./out might need this) just in case the compiler is panic-ing. This means in both compile.sh and evaluate.sh ...

EDIT2: or maybe another env var could be introduced which would change the default to always show backtrace, unless RUST_NOBACKTRACE is set, and since playpen cannot set any vars, rust-playpen will have backtrace be shown by default. Unfortunately this would also mean you cannot turn it off, which might be necessary to reproduce certain output... so it's not an acceptable solution (for me). (not to mention that changing a default like that is already a huge no no)

EDIT3: for what is worth, this seems to work:

$ sudo ./playpen ./sandbox --mount-proc --user=manj1 --syscalls-file=./whitelist -l -- bash -c 'export RUST_BACKTRACE=1;set|grep -i rust'

BASH_EXECUTION_STRING='export RUST_BACKTRACE=1;set|grep -i rust'
RUST_BACKTRACE=1
_=RUST_BACKTRACE

EDIT4: ok, I just realized that this exists and it's already setting an env var (TERM)

EDIT7: I have a workable implementation that turns on RUST_BACKTRACE only when Debug (but not Stable) is selected in rust-playpen... will submit a PR soon...

[respeccing]

Can probably close this one now.