tools/profile: fix kernel delimiter when folding

[graphaelli]

When combining delmiiter and folding options: profile -d -f, this exception is thrown:

Traceback (most recent call last):
  File "./profile", line 337, in <module>
    line.extend(b["-"] if (need_delimiter and k.kernel_stack_id >= 0 and k.user_stack_id >= 0) else [])
  File "/usr/local/lib/python2.7/dist-packages/bcc/__init__.py", line 508, in __getitem__
    self.tables[key] = self.get_table(key)
  File "/usr/local/lib/python2.7/dist-packages/bcc/__init__.py", line 493, in get_table
    raise KeyError
KeyError

This change eliminates the delimiter when folding is enabled.

[yonghong-song]

[buildbot, test this please]

[yonghong-song]

[buildbot, ok to test]

[yonghong-song]

[buildbot, test this please]

[brendangregg]

If you specify a delimiter you should get it, in the folded output. I have used them in flame graphs on purpose.

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[graphaelli]

@brendangregg That makes sense to me but I was trying to address the bug rather than introduce new functionality, happy to do it all at once here. How do you usually represent the delimiter in the flamegraph? Is the issue just that

bcc/tools/profile.py

Line 337 in 9b6a0e3

line.extend(b["-"] if (need_delimiter and k.kernel_stack_id >= 0 and k.user_stack_id >= 0) else [])

should be b"[-]" ? That looks like:

[graphaelli]

pushed a commit reverting the original change with a fix that retains the delimiter

[yonghong-song]

[buildbot, test this please]