Exceptions aren't enough to debug complicated code paths like debug info
discovery or stack unwinding. We really need logs for that, so let's add
a small logging framework. By default, we log to stderr, but we also
provide a way to direct logs to a different file, or even an arbitrary
callback so that logs can be directed to the application's logging
library of choice.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
drgn is currently licensed as GPLv3+. Part of the long term vision for
drgn is that other projects can use it as a library providing
programmatic interfaces for debugger functionality. A more permissive
license is better suited to this goal. We decided on LGPLv2.1+ as a good
balance between software freedom and permissiveness.
All contributors not employed by Meta were contacted via email and
consented to the license change. The only exception was the author of
commit c4fbf7e589 ("libdrgn: fix for compilation error"), who did not
respond. That commit reverted a single line of code to one originally
written by me in commit 640b1c011d ("libdrgn: embed DWARF index in
DWARF info cache").
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Instead of string_builder_finalize(), which leaves the string_builder in
an undefined state (according to the documentation, at least), define
string_builder_null_terminate(), which documents exactly what it does.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Like drgn_error_fwrite(), but writes to a file descriptor instead of a
stdio stream. This will be used for logging.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
drgn_error_fwrite() only calls string_builder_append_error() to get
special formatting for DRGN_ERROR_OS, but DRGN_ERROR_FAULT also needs
special formatting. Rather than needing to keep drgn_error_fwrite() and
string_builder_append_error() in sync, define them both in terms of a
common macro.
Fixes: 80fef04c70 ("Add address attribute to FaultError exception")
Signed-off-by: Omar Sandoval <osandov@osandov.com>
I was going to add an Object.available_ attribute, but that made me
realize that the naming is somewhat ambiguous, as a reference object
with an invalid address might also be considered "unavailable" by users.
Use the name "absent" instead, which is more clear: the object isn't
there at all.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
There are some situations where we can find an object but can't
determine its value, like local variables that have been optimized out,
inlined functions without a concrete instance, and pure virtual methods.
It's still useful to get some information from these objects, namely
their types. Let's add the concept of an "unavailable" object, which is
an object with a known type but unknown value/address.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
I recently hit a couple of CI failures caused by relying on transitive
includes that weren't always present. include-what-you-use is a
Clang-based tool that helps with this. It's a bit finicky and noisy, so
this adds scripts/iwyu.py to make running it more convenient (but not
reliable enough to automate it in Travis).
This cleans up all reasonable include-what-you-use warnings and
reorganizes a few header files.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
drgn was originally my side project, but for awhile now it's also been
my work project. Update the copyright headers to reflect this, and add a
copyright header to various files that were missing it.
We're too inconsistent with how we use these for them to be useful (and
it's impossible to distinguish between a format error and some other
error from libelf/libdw/libdwfl), so let's just get rid of them and make
it all DRGN_ERROR_OTHER/Exception.
Currently, finders indicate a non-fatal lookup error by setting the type
member to NULL. This won't work when we replace the symbol finder with
an object finder (which shouldn't modify the object on failure).
Instead, use a static error for this purpose.
libdwfl is the elfutils "DWARF frontend library". It has high-level
functionality for looking up symbols, walking stack traces, etc. In
order to use this functionality, we need to report our debugging
information through libdwfl. For userspace programs, libdwfl has a much
better implementation than drgn for automatically finding debug
information from a core dump or PID. However, for the kernel, libdwfl
has a few issues:
- It only supports finding debug information for the running kernel, not
vmcores.
- It determines the vmlinux address range by reading /proc/kallsyms,
which is slow (~70ms on my machine).
- If separate debug information isn't available for a kernel module, it
finds it by walking /lib/modules/$(uname -r)/kernel; this is repeated
for every module.
- It doesn't find kernel modules with names containing both dashes and
underscores (e.g., aes-x86_64).
Luckily, drgn already solved all of these problems, and with some
effort, we can keep doing it ourselves and report it to libdwfl.
The conversion replaces a bunch of code for dealing with userspace core
dump notes, /proc/$pid/maps, and relocations.
There are some cases where we format a path (e.g., with asprintf()) and
keep it around only in case of errors. Add drgn_error_format_os() so we
can just reformat it if we hit the error, which simplifies cleanup.
The current mixed Python/C implementation works well, but it has a
couple of important limitations:
- It's too slow for some common use cases, like iterating over large
data structures.
- It can't be reused in utilities written in other languages.
This replaces the internals with a new library written in C, libdrgn. It
includes Python bindings with mostly the same public interface as
before, with some important improvements:
- Types are now represented by a single Type class rather than the messy
polymorphism in the Python implementation.
- Qualifiers are a bitmask instead of a set of strings.
- Bit fields are not considered a separate type.
- The lvalue/rvalue terminology is replaced with reference/value.
- Structure, union, and array values are better supported.
- Function objects are supported.
- Program distinguishes between lookups of variables, constants, and
functions.
The C rewrite is about 6x as fast as the original Python when using the
Python bindings, and about 8x when using the C API directly.
Currently, the exposed API in C is fairly conservative. In the future,
the memory reader, type index, and object index APIs will probably be
exposed for more flexibility.
