[DTrace-devel] [PATCH v3 0/6] usdt typed args, translators and arg remapping

[Kris Van Hees]

Can you please rebase on github's devel?  Eugene's USDT work is on there and
that impacts patches 5/6 and 6/6.

Also, 1/6 is already on devel.

Please also searc hfor any occurences of /remap/ and fix those to use the
more consistent "map" and "mapping" language.

On Wed, Oct 30, 2024 at 12:08:44PM +0000, Nick Alcock wrote:
> This series adds back support for the probe foo (...) : (...) syntax
> in USDT provider definitions.  The dtprobed side is routine, pulling
> in the DOF and adding it to a new set of dof_parser.h records fed
> through to the DOF stash and ultimately to dt_pid.c and eventually
> dt_prov_uprobe.c: the end result is that the DOF for a given probe's
> remappings ends up in the dt_uprobe_t in more or less the same form
> as it was in the DOF.
> 
> After that things get tricky, because we want to remap not only arg[N] but
> also argN references (the single existing test for USDT arg remapping
> verifies that this works), but the SDT machinery depends on argN being
> unremapped!  So we do the remapping in dt_prov_uprobe.c while reshuffling
> things into dt_argdesc_t's, and tell the higher layers that no arg remapping
> is ever being performed, then do the remapping in the trampoline by
> physically reshuffling the arguments.  This seems to work without breaking
> SDT on all supported architectures, and is surprisingly simple (at least, it
> surprised me: multiple places where I thought I'd need hundreds of lines of
> complex code turned out to need only three or four lines).
> 
> New tests are added to verify that USDT translators work when types change,
> when arg counts change, and when there are no args at all, and that dtrace
> -vln produces the right output (all previous tests for USDT -vln, translated
> or not, are currently disabled because they all use wildcards: this new one
> doesn't).
> 
> We also fix a couple of tiny error-related bugs encountered in the
> course of development, one in usdt, one related to the print action.
> 
> Changes since v2:
>   Populate dt_argdesc_t's in USDT probe discovery rather than in
>   probe_info.
> 
> Changes since v1:
>   Adapted to review comments (all comments but the stuff around
>   trampolines and arg mapping, which I don't understand well
>   enough to implement); in particular track xlated args and
>   mappings together, and move from a flags word in the
>   dof_parser struct's DIT_PROBE record to an arg count
> 
> Nick Alcock (6):
>   error: add missing EDT_PRINT entry
>   usdt: get arg types and xlations into DTrace from the DOF
>   dtprobed: stop skipping zero-tracepoint probes in dof_stash.c
>   cg: add argument mapping in the trampoline
>   usdt: typed args and arg mapping
>   usdt: fix create_underlying error path
> 
>  dtprobed/dof_stash.c                          |  21 +--
>  dtprobed/dtprobed.c                           |  10 +-
>  include/dtrace/pid.h                          |   7 +
>  libcommon/dof_parser.c                        | 150 ++++++++++++----
>  libcommon/dof_parser.h                        |  64 ++++++-
>  libdtrace/dt_cg.c                             |  36 +++-
>  libdtrace/dt_cg.h                             |   1 +
>  libdtrace/dt_error.c                          |   3 +-
>  libdtrace/dt_pid.c                            |  60 +++++++
>  libdtrace/dt_prov_uprobe.c                    | 168 +++++++++++++++++-
>  test/triggers/usdt-tst-argmap-prov.d          |   5 +-
>  test/triggers/usdt-tst-argmap.c               |   5 +-
>  .../dtrace-util/tst.ListProbesArgsUSDT.r      |  34 ++++
>  .../dtrace-util/tst.ListProbesArgsUSDT.r.p    |   2 +
>  .../dtrace-util/tst.ListProbesArgsUSDT.sh     |  83 +++++++++
>  test/unittest/usdt/err.argmap-null.d          |  40 +++++
>  test/unittest/usdt/err.argmap-null.r          |   2 +
>  test/unittest/usdt/err.argmap-null.r.p        |   2 +
>  test/unittest/usdt/tst.argmap-null.d          |  32 ++++
>  test/unittest/usdt/tst.argmap-typed-partial.d |  49 +++++
>  test/unittest/usdt/tst.argmap-typed.d         |  48 +++++
>  test/unittest/usdt/tst.argmap.d               |   3 +-
>  test/utils/showUSDT.c                         |   5 +-
>  23 files changed, 759 insertions(+), 71 deletions(-)
>  create mode 100644 test/unittest/dtrace-util/tst.ListProbesArgsUSDT.r
>  create mode 100755 test/unittest/dtrace-util/tst.ListProbesArgsUSDT.r.p
>  create mode 100755 test/unittest/dtrace-util/tst.ListProbesArgsUSDT.sh
>  create mode 100644 test/unittest/usdt/err.argmap-null.d
>  create mode 100644 test/unittest/usdt/err.argmap-null.r
>  create mode 100755 test/unittest/usdt/err.argmap-null.r.p
>  create mode 100644 test/unittest/usdt/tst.argmap-null.d
>  create mode 100644 test/unittest/usdt/tst.argmap-typed-partial.d
>  create mode 100644 test/unittest/usdt/tst.argmap-typed.d
> 
> 
> base-commit: 8a1264bf0e818c8624be250eb5174714b62ed93c
> -- 
> 2.46.0.278.g36e3a12567
>