Sandbox should print better error message on execvp failure

[philwo]

Reported by user here: https://groups.google.com/forum/#!msg/bazel-discuss/T5KRcV5k9aA/Sdk07EC5BQAJ

The sandbox gave this rather unhelpful error log when it tried to execute a non-existing file:

$ bazel build  --sandbox_debug /base:hello_world
INFO: Found 1 target...
ERROR: /home/michiel/src/renew/base/BUILD:8:1: C++ compilation of rule '//base:hello_world' failed: linux-sandbox failed: error executing command /home/michiel/.cache/bazel/_bazel_michiel/b2baa5abb6f86343b08f67d0e9096f8a/execroot/renew/_bin/linux-sandbox ... (remaining 33 argument(s) skipped).
src/main/tools/linux-sandbox-pid1.cc:180: tmpfs: /tmp
src/main/tools/linux-sandbox-pid1.cc:298: remount ro: /tmp/sandbox.rwVjx7
src/main/tools/linux-sandbox-pid1.cc:298: remount ro: /tmp/sandbox.rwVjx7/dev
src/main/tools/linux-sandbox-pid1.cc:298: remount ro: /tmp/sandbox.rwVjx7/dev/pts
src/main/tools/linux-sandbox-pid1.cc:298: remount ro: /tmp/sandbox.rwVjx7/run
src/main/tools/linux-sandbox-pid1.cc:298: remount ro: /tmp/sandbox.rwVjx7/run/lock
src/main/tools/linux-sandbox-pid1.cc:298: remount ro: /tmp/sandbox.rwVjx7/run/shm
src/main/tools/linux-sandbox-pid1.cc:298: remount ro: /tmp/sandbox.rwVjx7/run/user
src/main/tools/linux-sandbox-pid1.cc:298: remount ro: /tmp/sandbox.rwVjx7/run/user/1000/gvfs
src/main/tools/linux-sandbox-pid1.cc:298: remount ro: /tmp/sandbox.rwVjx7/run/rpc_pipefs
src/main/tools/linux-sandbox-pid1.cc:298: remount ro: /tmp/sandbox.rwVjx7/sys
src/main/tools/linux-sandbox-pid1.cc:298: remount ro: /tmp/sandbox.rwVjx7/sys/fs/cgroup
src/main/tools/linux-sandbox-pid1.cc:298: remount ro: /tmp/sandbox.rwVjx7/sys/fs/cgroup/systemd
src/main/tools/linux-sandbox-pid1.cc:298: remount ro: /tmp/sandbox.rwVjx7/sys/fs/fuse/connections
src/main/tools/linux-sandbox-pid1.cc:298: remount ro: /tmp/sandbox.rwVjx7/sys/kernel/debug
src/main/tools/linux-sandbox-pid1.cc:298: remount ro: /tmp/sandbox.rwVjx7/sys/kernel/security
src/main/tools/linux-sandbox-pid1.cc:298: remount ro: /tmp/sandbox.rwVjx7/sys/fs/pstore
src/main/tools/linux-sandbox-pid1.cc:298: remount ro: /tmp/sandbox.rwVjx7/proc
src/main/tools/linux-sandbox-pid1.cc:298: remount ro: /tmp/sandbox.rwVjx7/proc/sys/fs/binfmt_misc
src/main/tools/linux-sandbox-pid1.cc:298: remount ro: /tmp/sandbox.rwVjx7/home
src/main/tools/linux-sandbox-pid1.cc:298: remount ro: /tmp/sandbox.rwVjx7/usr/local
src/main/tools/linux-sandbox-pid1.cc:298: remount ro: /tmp/sandbox.rwVjx7/nas
src/main/tools/linux-sandbox-pid1.cc:298: remount rw: /tmp/sandbox.rwVjx7/tmp
src/main/tools/linux-sandbox-pid1.cc:298: remount rw: /tmp/sandbox.rwVjx7/home/michiel/.cache/bazel/_bazel_michiel/b2baa5abb6f86343b08f67d0e9096f8a/bazel-sandbox/4e0fb7f2-101d-4dc9-84df-d4fc72a07078-0/execroot
src/main/tools/linux-sandbox-pid1.cc:439: "execvp(0x7ffc80bb8bc9, 0x8e8980)": No such file or directory

It would be great if we could print the actual path used in execvp() here.

[damienmg]

ping @philwo: can this be done this week?

[philwo]

I'm sending a fix for this now.