[Bug runtime/23435] New: stapbpf transport layer can swallow a message before exit()

["serhei.public at gmail dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=23435

            Bug ID: 23435
           Summary: stapbpf transport layer can swallow a message before
                    exit()
           Product: systemtap
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: runtime
          Assignee: systemtap at sourceware dot org
          Reporter: serhei.public at gmail dot com
  Target Milestone: ---

In the following test program:

probe kernel.function("vfs_read") {
  printf("a\n"); printf("b\n"); exit()
}

The stapbpf transport layer will see the following:

0: <tag>a
1: </tag>
2: <tag>b
3: </tag>
4: <tag></tag>

Because exit() sets exit_status before stapbpf reads this data, the empty
</tag> on line 1 will trigger the program to exit.

Similarly,

probe kernel.function("vfs_read") {
  printf(""); printf("b\n"); exit()
}

will also swallow the second message.

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