1. DTrace Release Notes
  2. DTrace Changelog
  3. 2.0.0-1.0 (Apr 24th, 2020)

2.0.0-1.0 (Apr 24th, 2020)

First errata of the standalone userspace implementation.

This is a pre-release with limited functionality.

New features:

  • BEGIN and END probes are functional. They are implemented using uprobes on trigger functions in libdtrace. The current implementation does not yet satisfy all documented semantics for these special probes. E.g. It is possible for a probe to be reported prior to the BEGIN probe.

  • The exit(n) action has been implemented. It terminates probing and will result in dtrace reporting the given return value <n> as its return code.

  • The flow-indent option -F has been implemented. Some of the heuristics present in DTrace 1.x are not available in this version - further code analysis is ongoing to determine whether they are necessary.

New options:

  • -xdisasm=n: Specify which disassembler listings to generate when the -S option is supplied. The value for <n> is the sum of any of the following:

    • 1 = After compilation and assembly of a program.

    • 2 = After linking in precompiled BPF functions (dependencies).

    • 4 = After final relocation processing (final program).

Bugfixes:

  • Various memory management issues such as memory leak and unsafe memory access operations were fixed.

  • Using local variables in D clauses could cause the compiler to generate instruction sequences where a load instruction for a local variable occurred before a store took place to that variable. The BPF verifier rejects such sequences. We now ensure that we do not load from stack locations that were never initialized.

  • The code generated for the post-increment operation resulted in the new value to be used as value of the expression. The value of the expression is now the old value.

  • Various issues were resolved concerning register use in the compiler. We are now using proper register spilling techniques to free up a sufficient amount of general purpose registers.

  • FBT return probes were not created correctly if an entry probe also existed for the same function. Both were getting attached to the same probe (either entry or return, depending on which was created first).

Internal changes:

  • Various helper functions have been implemented in C code that is compiled to BPF code using the GCC BPF cross compiler. These are available as an ELF object for linking with the dynamically generated code that the DTrace compiler produces. When D code has been compiled into BPF code, we resolve any references to precompiled BPF functions against this ELF object and add any functions used (and their dependencies) to the compiled program.

  • Various tests in the testsuite make use of the -xerrtags and -xdroptags options in dtrace to include specific error and drop tags in the error output. The testsuite engine did not enforce validation of these tags. Tests that specify a tag in their name err.<tag>.* and drp.<tag>.*) will now trigger validation that the specified tag is mentioned in the error output that dtrace produces.

  • Dynamically created system level probes (kprobes and uprobes are now grouped under a tracepoint group named dt_<pid>_<prv>[_<prb>] where <pid> is the PID of the dtrace process, <prv> the name of the probe provider, and <prb> the probe name. The _<prb> optional suffix is used for FBT probes to separate entry probes from return probes.