################################################################################
/usr/bin/python -u tools/mb/mb.py gen -f infra/mb/mb_config.pyl -m developer_default -b x64.release out.gn/x64.release

Writing """
is_debug = false
target_cpu = "x64"
""" to /media/veilblade/750G-01/downloads/v8/v8/out.gn/x64.release/args.gn.

/media/veilblade/750G-01/downloads/v8/v8/buildtools/linux64/gn gen out.gn/x64.release --check
-> returned 1
ERROR Can't find source root.
I could not find a ".gn" file in the current directory or any parent,
and the --root command-line argument was not specified.
GN gen failed: 1
Traceback (most recent call last):
File "tools/dev/v8gen.py", line 304, in
sys.exit(gen.main())
File "tools/dev/v8gen.py", line 298, in main
return self._options.func()
File "tools/dev/v8gen.py", line 166, in cmd_gen
gn_outdir,
File "tools/dev/v8gen.py", line 208, in _call_cmd
stderr=subprocess.STDOUT,
File "/usr/lib/python2.7/subprocess.py", line 574, in check_output
raise CalledProcessError(retcode, cmd, output=output)
subprocess.CalledProcessError: Command '['/usr/bin/python', '-u', 'tools/mb/mb.py', 'gen', '-f', 'infra/mb/mb_config.pyl', '-m', 'developer_default', '-b', 'x64.release', 'out.gn/x64.release']' returned non-zero exit status 1

there is some file or dir start with '.',did you upload those files