[INFO] cloning repository https://github.com/wrmthorne/Colatz-Calculator
[INFO] running `Command { std: "git" "-c" "credential.helper=" "-c" "credential.helper=/workspace/cargo-home/bin/git-credential-null" "clone" "--bare" "https://github.com/wrmthorne/Colatz-Calculator" "/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fwrmthorne%2FColatz-Calculator", kill_on_drop: false }`
[INFO] [stderr] Cloning into bare repository '/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fwrmthorne%2FColatz-Calculator'...
[INFO] running `Command { std: "git" "rev-parse" "HEAD", kill_on_drop: false }`
[INFO] [stdout] 23777995cd7e38add1da66ae9ff4c81e1616498c
[INFO] checking wrmthorne/Colatz-Calculator against master#91c0823ee63e793d990bb9fed898dc95b5d6db51 for pr-125741
[INFO] running `Command { std: "git" "clone" "/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fwrmthorne%2FColatz-Calculator" "/workspace/builds/worker-0-tc1/source", kill_on_drop: false }`
[INFO] [stderr] Cloning into '/workspace/builds/worker-0-tc1/source'...
[INFO] [stderr] done.
[INFO] validating manifest of git repo https://github.com/wrmthorne/Colatz-Calculator on toolchain 91c0823ee63e793d990bb9fed898dc95b5d6db51
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+91c0823ee63e793d990bb9fed898dc95b5d6db51" "metadata" "--manifest-path" "Cargo.toml" "--no-deps", kill_on_drop: false }`
[INFO] started tweaking git repo https://github.com/wrmthorne/Colatz-Calculator
[INFO] finished tweaking git repo https://github.com/wrmthorne/Colatz-Calculator
[INFO] tweaked toml for git repo https://github.com/wrmthorne/Colatz-Calculator written to /workspace/builds/worker-0-tc1/source/Cargo.toml
[INFO] crate git repo https://github.com/wrmthorne/Colatz-Calculator already has a lockfile, it will not be regenerated
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+91c0823ee63e793d990bb9fed898dc95b5d6db51" "fetch" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-0-tc1/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-0-tc1/source:/opt/rustwide/workdir:ro,Z" "-v" "/var/lib/crater-agent-workspace/cargo-home:/opt/rustwide/cargo-home:ro,Z" "-v" "/var/lib/crater-agent-workspace/rustup-home:/opt/rustwide/rustup-home:ro,Z" "-e" "SOURCE_DIR=/opt/rustwide/workdir" "-e" "CARGO_TARGET_DIR=/opt/rustwide/target" "-e" "CARGO_HOME=/opt/rustwide/cargo-home" "-e" "RUSTUP_HOME=/opt/rustwide/rustup-home" "-w" "/opt/rustwide/workdir" "-m" "1610612736" "--user" "0:0" "--network" "none" "ghcr.io/rust-lang/crates-build-env/linux@sha256:dff56e7819e73ed36160586b3445e93eb0be776c16704aeeded9c3fb668b2384" "/opt/rustwide/cargo-home/bin/cargo" "+91c0823ee63e793d990bb9fed898dc95b5d6db51" "metadata" "--no-deps" "--format-version=1", kill_on_drop: false }`
[INFO] [stdout] 3bc28fa0bad81915b30ae6411686ad7a2b0fd70bef75201f80ea72e43788449a
[INFO] running `Command { std: "docker" "start" "-a" "3bc28fa0bad81915b30ae6411686ad7a2b0fd70bef75201f80ea72e43788449a", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "inspect" "3bc28fa0bad81915b30ae6411686ad7a2b0fd70bef75201f80ea72e43788449a", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "3bc28fa0bad81915b30ae6411686ad7a2b0fd70bef75201f80ea72e43788449a", kill_on_drop: false }`
[INFO] [stdout] 3bc28fa0bad81915b30ae6411686ad7a2b0fd70bef75201f80ea72e43788449a
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-0-tc1/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-0-tc1/source:/opt/rustwide/workdir:ro,Z" "-v" "/var/lib/crater-agent-workspace/cargo-home:/opt/rustwide/cargo-home:ro,Z" "-v" "/var/lib/crater-agent-workspace/rustup-home:/opt/rustwide/rustup-home:ro,Z" "-e" "SOURCE_DIR=/opt/rustwide/workdir" "-e" "CARGO_TARGET_DIR=/opt/rustwide/target" "-e" "CARGO_INCREMENTAL=0" "-e" "RUST_BACKTRACE=full" "-e" "RUSTFLAGS=--cap-lints=forbid" "-e" "RUSTDOCFLAGS=--cap-lints=forbid" "-e" "CARGO_HOME=/opt/rustwide/cargo-home" "-e" "RUSTUP_HOME=/opt/rustwide/rustup-home" "-w" "/opt/rustwide/workdir" "-m" "1610612736" "--user" "0:0" "--network" "none" "ghcr.io/rust-lang/crates-build-env/linux@sha256:dff56e7819e73ed36160586b3445e93eb0be776c16704aeeded9c3fb668b2384" "/opt/rustwide/cargo-home/bin/cargo" "+91c0823ee63e793d990bb9fed898dc95b5d6db51" "check" "--frozen" "--all" "--all-targets" "--message-format=json", kill_on_drop: false }`
[INFO] [stdout] 5c8a7464fcf21f0b53a92583bd97de6bda0f9064836536cc6e2cd6734dc8677d
[INFO] running `Command { std: "docker" "start" "-a" "5c8a7464fcf21f0b53a92583bd97de6bda0f9064836536cc6e2cd6734dc8677d", kill_on_drop: false }`
[INFO] [stderr] time="2024-06-05T01:06:19Z" level=error msg="error waiting for container: "
[INFO] [stderr] Error response from daemon: mkdir /var/lib/docker/overlay2/0730bbab9457175af2de50838e709fb4aff1b4808721cc51e2f98623f8468d92/merged: no space left on device
[INFO] running `Command { std: "docker" "inspect" "5c8a7464fcf21f0b53a92583bd97de6bda0f9064836536cc6e2cd6734dc8677d", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "5c8a7464fcf21f0b53a92583bd97de6bda0f9064836536cc6e2cd6734dc8677d", kill_on_drop: false }`
[INFO] [stdout] 5c8a7464fcf21f0b53a92583bd97de6bda0f9064836536cc6e2cd6734dc8677d
[INFO] checking wrmthorne/Colatz-Calculator against try#0525276e4a85ae0a91f6f7447e501e2981e77908 for pr-125741
[INFO] running `Command { std: "git" "clone" "/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fwrmthorne%2FColatz-Calculator" "/workspace/builds/worker-0-tc2/source", kill_on_drop: false }`
[INFO] [stderr] Cloning into '/workspace/builds/worker-0-tc2/source'...
[INFO] [stderr] done.
[INFO] validating manifest of git repo https://github.com/wrmthorne/Colatz-Calculator on toolchain 0525276e4a85ae0a91f6f7447e501e2981e77908
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0525276e4a85ae0a91f6f7447e501e2981e77908" "metadata" "--manifest-path" "Cargo.toml" "--no-deps", kill_on_drop: false }`
[INFO] started tweaking git repo https://github.com/wrmthorne/Colatz-Calculator
[INFO] finished tweaking git repo https://github.com/wrmthorne/Colatz-Calculator
[INFO] tweaked toml for git repo https://github.com/wrmthorne/Colatz-Calculator written to /workspace/builds/worker-0-tc2/source/Cargo.toml
[INFO] crate git repo https://github.com/wrmthorne/Colatz-Calculator already has a lockfile, it will not be regenerated
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0525276e4a85ae0a91f6f7447e501e2981e77908" "fetch" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-0-tc2/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-0-tc2/source:/opt/rustwide/workdir:ro,Z" "-v" "/var/lib/crater-agent-workspace/cargo-home:/opt/rustwide/cargo-home:ro,Z" "-v" "/var/lib/crater-agent-workspace/rustup-home:/opt/rustwide/rustup-home:ro,Z" "-e" "SOURCE_DIR=/opt/rustwide/workdir" "-e" "CARGO_TARGET_DIR=/opt/rustwide/target" "-e" "CARGO_HOME=/opt/rustwide/cargo-home" "-e" "RUSTUP_HOME=/opt/rustwide/rustup-home" "-w" "/opt/rustwide/workdir" "-m" "1610612736" "--user" "0:0" "--network" "none" "ghcr.io/rust-lang/crates-build-env/linux@sha256:dff56e7819e73ed36160586b3445e93eb0be776c16704aeeded9c3fb668b2384" "/opt/rustwide/cargo-home/bin/cargo" "+0525276e4a85ae0a91f6f7447e501e2981e77908" "metadata" "--no-deps" "--format-version=1", kill_on_drop: false }`
[INFO] [stdout] 61c35dea223ba0ebfc861032765995e0c750e99616be460b5b9620cddaf335ad
[INFO] running `Command { std: "docker" "start" "-a" "61c35dea223ba0ebfc861032765995e0c750e99616be460b5b9620cddaf335ad", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "inspect" "61c35dea223ba0ebfc861032765995e0c750e99616be460b5b9620cddaf335ad", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "61c35dea223ba0ebfc861032765995e0c750e99616be460b5b9620cddaf335ad", kill_on_drop: false }`
[INFO] [stdout] 61c35dea223ba0ebfc861032765995e0c750e99616be460b5b9620cddaf335ad
[INFO] checking wrmthorne/Colatz-Calculator against try#0525276e4a85ae0a91f6f7447e501e2981e77908 for pr-125741
[INFO] running `Command { std: "git" "clone" "/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fwrmthorne%2FColatz-Calculator" "/workspace/builds/worker-0-tc2/source", kill_on_drop: false }`
[INFO] [stderr] Cloning into '/workspace/builds/worker-0-tc2/source'...
[INFO] [stderr] done.
[INFO] validating manifest of git repo https://github.com/wrmthorne/Colatz-Calculator on toolchain 0525276e4a85ae0a91f6f7447e501e2981e77908
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0525276e4a85ae0a91f6f7447e501e2981e77908" "metadata" "--manifest-path" "Cargo.toml" "--no-deps", kill_on_drop: false }`
[INFO] started tweaking git repo https://github.com/wrmthorne/Colatz-Calculator
[INFO] finished tweaking git repo https://github.com/wrmthorne/Colatz-Calculator
[INFO] tweaked toml for git repo https://github.com/wrmthorne/Colatz-Calculator written to /workspace/builds/worker-0-tc2/source/Cargo.toml
[INFO] crate git repo https://github.com/wrmthorne/Colatz-Calculator already has a lockfile, it will not be regenerated
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0525276e4a85ae0a91f6f7447e501e2981e77908" "fetch" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-0-tc2/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-0-tc2/source:/opt/rustwide/workdir:ro,Z" "-v" "/var/lib/crater-agent-workspace/cargo-home:/opt/rustwide/cargo-home:ro,Z" "-v" "/var/lib/crater-agent-workspace/rustup-home:/opt/rustwide/rustup-home:ro,Z" "-e" "SOURCE_DIR=/opt/rustwide/workdir" "-e" "CARGO_TARGET_DIR=/opt/rustwide/target" "-e" "CARGO_HOME=/opt/rustwide/cargo-home" "-e" "RUSTUP_HOME=/opt/rustwide/rustup-home" "-w" "/opt/rustwide/workdir" "-m" "1610612736" "--user" "0:0" "--network" "none" "ghcr.io/rust-lang/crates-build-env/linux@sha256:dff56e7819e73ed36160586b3445e93eb0be776c16704aeeded9c3fb668b2384" "/opt/rustwide/cargo-home/bin/cargo" "+0525276e4a85ae0a91f6f7447e501e2981e77908" "metadata" "--no-deps" "--format-version=1", kill_on_drop: false }`
[INFO] [stderr] Error response from daemon: write /var/lib/docker/containers/d44356e8656b53351f51e2972dbe5169934055f55c01ebb7e0070c7db6996ddf/.tmp-hostconfig.json2175387548: no space left on device
[INFO] checking wrmthorne/Colatz-Calculator against try#0525276e4a85ae0a91f6f7447e501e2981e77908 for pr-125741
[INFO] running `Command { std: "git" "clone" "/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fwrmthorne%2FColatz-Calculator" "/workspace/builds/worker-0-tc2/source", kill_on_drop: false }`
[INFO] [stderr] Cloning into '/workspace/builds/worker-0-tc2/source'...
[INFO] [stderr] done.
[INFO] validating manifest of git repo https://github.com/wrmthorne/Colatz-Calculator on toolchain 0525276e4a85ae0a91f6f7447e501e2981e77908
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0525276e4a85ae0a91f6f7447e501e2981e77908" "metadata" "--manifest-path" "Cargo.toml" "--no-deps", kill_on_drop: false }`
[INFO] started tweaking git repo https://github.com/wrmthorne/Colatz-Calculator
[INFO] finished tweaking git repo https://github.com/wrmthorne/Colatz-Calculator
[INFO] tweaked toml for git repo https://github.com/wrmthorne/Colatz-Calculator written to /workspace/builds/worker-0-tc2/source/Cargo.toml
[INFO] crate git repo https://github.com/wrmthorne/Colatz-Calculator already has a lockfile, it will not be regenerated
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0525276e4a85ae0a91f6f7447e501e2981e77908" "fetch" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-0-tc2/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-0-tc2/source:/opt/rustwide/workdir:ro,Z" "-v" "/var/lib/crater-agent-workspace/cargo-home:/opt/rustwide/cargo-home:ro,Z" "-v" "/var/lib/crater-agent-workspace/rustup-home:/opt/rustwide/rustup-home:ro,Z" "-e" "SOURCE_DIR=/opt/rustwide/workdir" "-e" "CARGO_TARGET_DIR=/opt/rustwide/target" "-e" "CARGO_HOME=/opt/rustwide/cargo-home" "-e" "RUSTUP_HOME=/opt/rustwide/rustup-home" "-w" "/opt/rustwide/workdir" "-m" "1610612736" "--user" "0:0" "--network" "none" "ghcr.io/rust-lang/crates-build-env/linux@sha256:dff56e7819e73ed36160586b3445e93eb0be776c16704aeeded9c3fb668b2384" "/opt/rustwide/cargo-home/bin/cargo" "+0525276e4a85ae0a91f6f7447e501e2981e77908" "metadata" "--no-deps" "--format-version=1", kill_on_drop: false }`
[INFO] [stderr] Error response from daemon: mkdir /var/lib/docker/overlay2/1e85e211f6705807b98935c76a45d311f93d6e3f957a41ec5b9f77f07f02782f/merged/opt/rustwide/workdir: no space left on device
[INFO] checking wrmthorne/Colatz-Calculator against try#0525276e4a85ae0a91f6f7447e501e2981e77908 for pr-125741
[INFO] running `Command { std: "git" "clone" "/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fwrmthorne%2FColatz-Calculator" "/workspace/builds/worker-0-tc2/source", kill_on_drop: false }`
[INFO] [stderr] Cloning into '/workspace/builds/worker-0-tc2/source'...
[INFO] [stderr] done.
[INFO] validating manifest of git repo https://github.com/wrmthorne/Colatz-Calculator on toolchain 0525276e4a85ae0a91f6f7447e501e2981e77908
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0525276e4a85ae0a91f6f7447e501e2981e77908" "metadata" "--manifest-path" "Cargo.toml" "--no-deps", kill_on_drop: false }`
[INFO] started tweaking git repo https://github.com/wrmthorne/Colatz-Calculator
[INFO] finished tweaking git repo https://github.com/wrmthorne/Colatz-Calculator
[INFO] tweaked toml for git repo https://github.com/wrmthorne/Colatz-Calculator written to /workspace/builds/worker-0-tc2/source/Cargo.toml
[INFO] crate git repo https://github.com/wrmthorne/Colatz-Calculator already has a lockfile, it will not be regenerated
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0525276e4a85ae0a91f6f7447e501e2981e77908" "fetch" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-0-tc2/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-0-tc2/source:/opt/rustwide/workdir:ro,Z" "-v" "/var/lib/crater-agent-workspace/cargo-home:/opt/rustwide/cargo-home:ro,Z" "-v" "/var/lib/crater-agent-workspace/rustup-home:/opt/rustwide/rustup-home:ro,Z" "-e" "SOURCE_DIR=/opt/rustwide/workdir" "-e" "CARGO_TARGET_DIR=/opt/rustwide/target" "-e" "CARGO_HOME=/opt/rustwide/cargo-home" "-e" "RUSTUP_HOME=/opt/rustwide/rustup-home" "-w" "/opt/rustwide/workdir" "-m" "1610612736" "--user" "0:0" "--network" "none" "ghcr.io/rust-lang/crates-build-env/linux@sha256:dff56e7819e73ed36160586b3445e93eb0be776c16704aeeded9c3fb668b2384" "/opt/rustwide/cargo-home/bin/cargo" "+0525276e4a85ae0a91f6f7447e501e2981e77908" "metadata" "--no-deps" "--format-version=1", kill_on_drop: false }`
[INFO] [stderr] Error response from daemon: mkdir /var/lib/docker/overlay2/b5f9dc898794ca27ef2827be6185e779699932b53ab7a8eee140d47ad3f85cd1/merged/opt/rustwide: no space left on device
[INFO] checking wrmthorne/Colatz-Calculator against try#0525276e4a85ae0a91f6f7447e501e2981e77908 for pr-125741
[INFO] running `Command { std: "git" "clone" "/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fwrmthorne%2FColatz-Calculator" "/workspace/builds/worker-0-tc2/source", kill_on_drop: false }`
[INFO] [stderr] Cloning into '/workspace/builds/worker-0-tc2/source'...
[INFO] [stderr] done.
[INFO] validating manifest of git repo https://github.com/wrmthorne/Colatz-Calculator on toolchain 0525276e4a85ae0a91f6f7447e501e2981e77908
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0525276e4a85ae0a91f6f7447e501e2981e77908" "metadata" "--manifest-path" "Cargo.toml" "--no-deps", kill_on_drop: false }`
[INFO] started tweaking git repo https://github.com/wrmthorne/Colatz-Calculator
[INFO] finished tweaking git repo https://github.com/wrmthorne/Colatz-Calculator
[INFO] tweaked toml for git repo https://github.com/wrmthorne/Colatz-Calculator written to /workspace/builds/worker-0-tc2/source/Cargo.toml
[INFO] crate git repo https://github.com/wrmthorne/Colatz-Calculator already has a lockfile, it will not be regenerated
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0525276e4a85ae0a91f6f7447e501e2981e77908" "fetch" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-0-tc2/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-0-tc2/source:/opt/rustwide/workdir:ro,Z" "-v" "/var/lib/crater-agent-workspace/cargo-home:/opt/rustwide/cargo-home:ro,Z" "-v" "/var/lib/crater-agent-workspace/rustup-home:/opt/rustwide/rustup-home:ro,Z" "-e" "SOURCE_DIR=/opt/rustwide/workdir" "-e" "CARGO_TARGET_DIR=/opt/rustwide/target" "-e" "CARGO_HOME=/opt/rustwide/cargo-home" "-e" "RUSTUP_HOME=/opt/rustwide/rustup-home" "-w" "/opt/rustwide/workdir" "-m" "1610612736" "--user" "0:0" "--network" "none" "ghcr.io/rust-lang/crates-build-env/linux@sha256:dff56e7819e73ed36160586b3445e93eb0be776c16704aeeded9c3fb668b2384" "/opt/rustwide/cargo-home/bin/cargo" "+0525276e4a85ae0a91f6f7447e501e2981e77908" "metadata" "--no-deps" "--format-version=1", kill_on_drop: false }`
[INFO] [stderr] Error response from daemon: chown /var/lib/docker/overlay2/e2be4820b96247358e501766c14e06adcd449b9f01c15b3017fd12e1ded5f117/work/work: no such file or directory
[ERROR] this task or one of its parent failed!
[ERROR] command failed: exit status: 1
[ERROR] note: run with `RUST_BACKTRACE=1` to display a backtrace.