For stack trace support, we'll need to have some architecture-specific
functionality. drgn's current notion of an architecture doesn't actually
include the instruction set architecture. This change expands it to a
"platform", which includes the ISA as well as the existing flags.
struct drgn_symbol doesn't really represent a symbol; it's just an
object which hasn't been fully initialized (see c2be52dff0 ("libdrgn:
rename object index to symbol index"), it used to be called a "partial
object"). For stack traces, we're going to have a notion of a symbol
that more closely represents an ELF symbol, so let's get rid of the
temporary struct drgn_symbol representation and just return an object
directly.
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.
The current array-based memory reader has a bug in the following
scenario:
prog.add_memory_segment(0xffff0000, 128, ...)
# This should replace a subset of the first segment.
prog.add_memory_segment(0xffff0020, 32, ...)
# This moves the first segment back to the front of the array.
prog.read(0xffff0000, 32)
# This finds the first segment instead of the second segment.
prog.read(0xffff0032, 32)
Fix it by using the newly-added splay tree. This also splits up the
virtual and physical memory segments into separate trees.
Currently, size_t and ptrdiff_t default to typedefs of the default
unsigned long and long, respectively, regardless of what the program
actually defines unsigned long or long as. Instead, make them refer the
whatever integer type (long, long long, or int) is the same size as the
word size.
Currently, programs can be created for three main use-cases: core dumps,
the running kernel, and a running process. However, internally, the
program memory, types, and symbols are pluggable. Expose that as a
callback API, which makes it possible to use drgn in much more creative
ways.
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.
It's silly to have these trival factory methods. Instead, directly
construct with Object() and add a new NULL() function. We also
automatically import these in interactive mode.
This is preparation for the next change, so that a Program can clean up
after itself. The Program will close the CoreReader, and the CoreReader
will close the underlying file.
ProgramObject.__dir__(), member_(), and container_of_() all check that
the relevant type is a struct or union, but they all need to allow
typedefs of structs or unions, as well.
We're currently also doing this check in __getattr__(), which is
unnecessary overhead in the common case. We can just check the exception
in the error case.
