For live userspace processes, we add a single [0, UINT64_MAX) memory
file segment for /proc/$pid/mem. Of course, not every address in that
range is valid; reading from an invalid address returns EIO. We should
translate this to a DRGN_ERROR_FAULT instead of DRGN_ERROR_OS, but only
for /proc/$pid/mem.
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.
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.
