[DTrace-devel] [PATCH v5 0/9] stapsdt provider: simple system-wide probing

[Alan Maguire]

On 04/03/2026 08:01, Alan Maguire wrote:
> This series adds wildcard support to stapsdt probes to allow
> tracing system-wide; this has caveats due to the way the kernel
> implements probe addition.  In essence, probes are added on a
> per-inode basis (actually in the VMA associated with the inode)
> so it is necessary to identify the file where probes are found.
> Probes will fire for existing and new processes (the RFC incorrectly
> said they will not work for existing binaries; they in fact do).
> 
> Patch 2 describes the approach; to facilitate systemwide tracing
> we need to tell DTrace the name of the binary/library via either
> using module absolute path (patch 1 updates parsing to support use
> of a '/' in a module descriptor to faciliate this support) or an
> module name; to expand this we then use [LD_LIBRARY_]PATH
> to resolve the full path.  ELF reading of the file and insertion
> of probes then proceeds in a similar manner to per-pid tracing.
> 
> Patches 3-8 test various aspects of systemwide probes; basic
> binary support, library support, listing support and is-enabled
> probes support, and use of absolute paths.
> 
> Tests ensure wildcards work for
> 
> 1. a process started prior to DTrace
> 2. a process started by DTrace (-c)
> 3. two processes started after DTrace is running
>    (via system())
> 
> Patch 9 updates docs to describe stapsdt wildcard support.
> 
> Changes since v4:
> 
> - Restrict '/' to module names (Kris, patch 1)
> - Name probes as provider0 rather than provider* (Kris, patch 2)

small clarification here; the name I'm referring to here is the
probeprov we see on _firing_ (or listing) not the one we'd use in the tuple in
a DTrace script; i.e. we still do:

$ sudo dtrace -n 'python*:/usr/lib64/libpython3.6m.so:: { printf("%s:%s:%s:%s\n", probeprov, probemod, probefunc, probename);}'

However we see:

  5   6734                            :line python0:/usr/lib64/libpython3.6m.so::line


> - Resync with devel branch
> 
> Changes since v3:
> 
> - Semaphores need to be more carefully declared to handle
>   the is-enabled case where the process is not running when
>   DTrace starts tracing; the kernel handles reference counts
>   so the probes must be added to the ".probes" section; see
>   patches 8/9 for how this is done.
> - Modified tests to start an instance of the test program
>  prior to DTrace execution and start two further during
>   DTrace execution; ensure we see probe firings for all
>   4 of these processes before declaring success (Kris,
>   patches 3, 4, 5, 8)
> 
> Changes since v2:
> 
> - support absolute paths (patch 1, 2)
> - add tests for absolute paths (patch 4, 7)
> - document systemwide probe support for listing/using absolute
>   paths (patch 9)
> 
> Changes since RFC:
> 
> - update documentation/commit messages to reflect that we also
>   catch existing programs/libraries when probes are enabled
> - fixup provider name for wildcard probes to be 'provider*'
>   rather than using the confusing 'provider-1' since the
>   latter is the concatenation of probename and pid (-1 is
>   used to connote all pids)
> - add test for is-enabled systemwide probes
> 
> Alan Maguire (9):
>   dt_lex: support '/' in probe descriptors
>   stapsdt provider: support systemwide probing
>   test: add systemwide stapsdt note test
>   test: add systemwide stapsdt note test using absolute path
>   test: add systemwide stapsdt note test for library
>   stapsdt: add test for listing systemwide probes in object
>   stapsdt: add test for listing systemwide probes in absolute path
>     object
>   stapsdt: add systemwide test for is-enabled probes
>   documentation: update stapsdt docs to describe wildcard support
> 
>  .../reference/dtrace_providers_stapsdt.md     |  91 +++++-
>  libdtrace/dt_lex.l                            |   2 +-
>  libdtrace/dt_pid.c                            | 174 +++++++++---
>  libdtrace/dt_prov_uprobe.c                    |  15 +-
>  libdtrace/dt_subr.c                           |   6 +
>  .../tst.stapsdt-notes-systemwide-abspath.r    |   5 +
>  .../tst.stapsdt-notes-systemwide-abspath.sh   |  89 ++++++
>  .../tst.stapsdt-notes-systemwide-isenabled.r  |  13 +
>  .../tst.stapsdt-notes-systemwide-isenabled.sh | 266 ++++++++++++++++++
>  .../tst.stapsdt-notes-systemwide-l-abspath.sh |  48 ++++
>  .../usdt/tst.stapsdt-notes-systemwide-l.sh    |  48 ++++
>  .../usdt/tst.stapsdt-notes-systemwide-lib.r   |  14 +
>  .../usdt/tst.stapsdt-notes-systemwide-lib.sh  | 215 ++++++++++++++
>  ...tst.stapsdt-notes-systemwide-lv-abspath.sh |  48 ++++
>  .../usdt/tst.stapsdt-notes-systemwide-lv.sh   |  48 ++++
>  .../usdt/tst.stapsdt-notes-systemwide.r       |   5 +
>  .../usdt/tst.stapsdt-notes-systemwide.sh      |  89 ++++++
>  17 files changed, 1125 insertions(+), 51 deletions(-)
>  create mode 100644 test/unittest/usdt/tst.stapsdt-notes-systemwide-abspath.r
>  create mode 100755 test/unittest/usdt/tst.stapsdt-notes-systemwide-abspath.sh
>  create mode 100644 test/unittest/usdt/tst.stapsdt-notes-systemwide-isenabled.r
>  create mode 100755 test/unittest/usdt/tst.stapsdt-notes-systemwide-isenabled.sh
>  create mode 100755 test/unittest/usdt/tst.stapsdt-notes-systemwide-l-abspath.sh
>  create mode 100755 test/unittest/usdt/tst.stapsdt-notes-systemwide-l.sh
>  create mode 100644 test/unittest/usdt/tst.stapsdt-notes-systemwide-lib.r
>  create mode 100755 test/unittest/usdt/tst.stapsdt-notes-systemwide-lib.sh
>  create mode 100755 test/unittest/usdt/tst.stapsdt-notes-systemwide-lv-abspath.sh
>  create mode 100755 test/unittest/usdt/tst.stapsdt-notes-systemwide-lv.sh
>  create mode 100644 test/unittest/usdt/tst.stapsdt-notes-systemwide.r
>  create mode 100755 test/unittest/usdt/tst.stapsdt-notes-systemwide.sh
>