Currently, we load debug information for every kernel module that we
find under /lib/modules/$(uname -r)/kernel. This has a few issues:
1. Distribution kernels have lots of modules (~3000 for Fedora and
Debian).
a) This can exceed the default soft limit on the number of open file
descriptors.
b) The mmap'd debug information can trip the overcommit heuristics
and cause OOM kills.
c) It can take a long time to parse all of the debug information.
2. Not all modules are under the "kernel" directory; some distros also
have an "extra" directory.
3. The user is not made aware of loaded kernel modules that don't have
debug information available.
So, instead of walking /lib/modules, walk the list of loaded kernel
modules and look up their debugging information.
const char * const * is not compatible with char * const *, so make
c_string_hash() and c_string_eq() macros so they can work with both
const char * and char * keys.
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.
Similar to "libdrgn: make memory reader pluggable with callbacks", we
want to support custom type indexes (imagine, e.g., using drgn to parse
a binary format). For now, this disables the dwarf index tests; we'll
have a better way to test them later, so let's not bother adding more
test scaffolding.
I've been planning to make memory readers pluggable (in order to support
use cases like, e.g., reading a core file over the network), but the
C-style "inheritance" drgn uses internally is awkward as a library
interface; it's much easier to just register a callback. This change
effectively makes drgn_memory_reader a mapping from a memory range to an
arbitrary callback. As a bonus, this means that read callbacks can be
mixed and matched; a part of memory can be in a core file, another part
can be in the executable file, and another part could be filled from an
arbitrary buffer.
Currently, we deduplicate files for userspace mappings manually.
However, to prepare for adding symbol files at runtime, move the
deduplication to DWARF index. In the future, we probably want to
deduplicate based on build ID, as well.
Relocations are only supposed to be applied to ET_REL files, not ET_EXEC
files like vmlinux. This hasn't been an issue with the kernel builds
that I've tested on because the relocations match the contents of the
section. However, on Fedora, the relocation sections don't match,
probably because they post-process the binary in some way. This leads to
completely bogus debug information being parsed by drgn_dwarf_index. Fix
it by only relocating ET_REL files.
autoreconf may successfully run autoconf but not automake, so we should
check that Makefile.in exists, not configure. Additionally, there also
seem to be some cases where configure fails but Makefile is still
generated. Make sure we delete the potentially-broken output if
autoreconf/configure failed.
