When profiling an app I kept getting "Failed instruments errored: blank" (ie. no reason for the error).
Turns out xctrace was printing "Target app exited" (there was a problem with my command line) to stdOUT and nothing to stdERR.
Looks like xctrace prints the interesting information to stdout instead of stderr in at least some scenarios, so including the output of both on failure.
When profiling an app I kept getting "Failed instruments errored: blank" (ie. no reason for the error). Turns out xctrace was printing "Target app exited" (there was a problem with my command line) to stdOUT and nothing to stdERR.
Looks like xctrace prints the interesting information to stdout instead of stderr in at least some scenarios, so including the output of both on failure.