[Bug runtime/22330] New: bpf: generate printf via event tuples, userspace formatting postprocessing

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[Bug runtime/22330] New: bpf: generate printf via event tuples, userspace formatting postprocessing

albert.aribaud at 3adev dot fr
https://sourceware.org/bugzilla/show_bug.cgi?id=22330

            Bug ID: 22330
           Summary: bpf: generate printf via event tuples, userspace
                    formatting postprocessing
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: runtime
          Assignee: systemtap at sourceware dot org
          Reporter: amerey at redhat dot com
  Target Milestone: ---

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[Bug runtime/22330] bpf: generate printf via event tuples, userspace formatting postprocessing

albert.aribaud at 3adev dot fr
https://sourceware.org/bugzilla/show_bug.cgi?id=22330

Serhei Makarov <serhei.public at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |serhei.public at gmail dot com

--- Comment #1 from Serhei Makarov <serhei.public at gmail dot com> ---
This is also relevant because the current trace_printk() mechanism is
discouraged on 'production kernels' and will log a prominent notice to that
effect to dmesg.

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[Bug bpf/22330] bpf: generate printf via event tuples, userspace formatting postprocessing

albert.aribaud at 3adev dot fr
In reply to this post by albert.aribaud at 3adev dot fr
https://sourceware.org/bugzilla/show_bug.cgi?id=22330

Serhei Makarov <me at serhei dot io> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |me at serhei dot io
          Component|runtime                     |bpf

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[Bug bpf/22330] bpf: generate printf via event tuples, userspace formatting postprocessing

albert.aribaud at 3adev dot fr
In reply to this post by albert.aribaud at 3adev dot fr
https://sourceware.org/bugzilla/show_bug.cgi?id=22330

--- Comment #2 from Serhei Makarov <me at serhei dot io> ---
As part of the reworking of printf() on stapbpf, large printf() invocations
should also be split up into a series of manageable ones. The following example
should work:

probe kernel.trace("netif_receive_skb"), kernel.trace("netif_rx"),
  kernel.trace("net_dev_queue"), kernel.trace("napi_gro_receive_entry") {
  printf("vars %s\n", $$vars);
}

Currently it fails with "too many arguments to print (19)".

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[Bug bpf/22330] bpf: generate printf via event tuples, userspace formatting postprocessing

albert.aribaud at 3adev dot fr
In reply to this post by albert.aribaud at 3adev dot fr
https://sourceware.org/bugzilla/show_bug.cgi?id=22330

Serhei Makarov <me at serhei dot io> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |23435, 23559


Referenced Bugs:

https://sourceware.org/bugzilla/show_bug.cgi?id=23435
[Bug 23435] stapbpf transport layer can swallow a message before exit()
https://sourceware.org/bugzilla/show_bug.cgi?id=23559
[Bug 23559] stapbpf string literal support for octal and hex escape codes
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[Bug bpf/22330] bpf: generate printf via event tuples, userspace formatting postprocessing

albert.aribaud at 3adev dot fr
In reply to this post by albert.aribaud at 3adev dot fr
https://sourceware.org/bugzilla/show_bug.cgi?id=22330

--- Comment #3 from Serhei Makarov <me at serhei dot io> ---
Another reason to rework printf() -- the trace_printk() implementation
hardcodes any string operands to 64 bytes:

https://github.com/torvalds/linux/blob/6b2edf27fe26c73cd67b6bf5ffb23dce882e1455/kernel/trace/bpf_trace.c#L226

Prioritizing this PR on account of the 64-byte trace_printk() limitation.

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[Bug bpf/22330] bpf: generate printf via event tuples, userspace formatting postprocessing

albert.aribaud at 3adev dot fr
In reply to this post by albert.aribaud at 3adev dot fr
https://sourceware.org/bugzilla/show_bug.cgi?id=22330

Serhei Makarov <me at serhei dot io> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|systemtap at sourceware dot org    |me at serhei dot io

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