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We currently handle DIEs with a DW_AT_specification attribute by parsing
the corresponding declaration to get the name and inserting the DIE as
usual. This has a couple of problems:
1. It only works if DW_AT_specification refers to the same compilation
unit, which is true for DW_FORM_ref{1,2,4,8,_udata}, but not
DW_FORM_ref_addr. As a result, drgn doesn't support the latter.
2. It assumes that the DIE with DW_AT_specification is in the correct
"scope". Unfortunately, this is not true for g++: for a variable
definition in a C++ namespace, it generates a DIE with
DW_AT_declaration as a child of the DW_TAG_namespace DIE and a DIE
which refers to the declaration with DW_AT_specification _outside_ of
the DW_TAG_namespace as a child of the DW_TAG_compilation_unit DIE.
Supporting both of these cases requires reworking how we handle
DW_AT_specification. This commit takes an approach of parsing the DWARF
data in two passes: the first pass reads the abbrevation and file name
tables and builds a map of instances of DW_AT_specification; the second
pass indexes DIEs as before, but ignores DIEs with DW_AT_specification
and handles DIEs with DW_AT_declaration by looking them up in the map
built by the first pass.
This approach is a 10-20% regression in indexing time in the benchmarks
I ran. Thankfully, it is not 100% slower for a couple of reasons. The
first is that the two passes are simpler than the original combined
pass. The second is that a decent part of the indexing time is spent
faulting in the mapped debugging information, which only needs to happen
once (even if the file is cached, minor page faults add non-negligible
overhead).
This doesn't handle DW_AT_specification "chains" yet, but neither did
the original code. If it is necessary, it shouldn't be too difficult to
add.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
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| .. | ||
| build-aux | ||
| elfutils | ||
| examples | ||
| include | ||
| m4 | ||
| python | ||
| .gitignore | ||
| arch_x86_64.c.in | ||
| binary_search_tree.h | ||
| cityhash.h | ||
| configure.ac | ||
| Doxyfile | ||
| drgn.h.in | ||
| dwarf_index.c | ||
| dwarf_index.h | ||
| dwarf_info_cache.c | ||
| dwarf_info_cache.h | ||
| error.c | ||
| error.h | ||
| hash_table.c | ||
| hash_table.h | ||
| helpers.h | ||
| internal.c | ||
| internal.h | ||
| kdump.c | ||
| language_c.c | ||
| language.c | ||
| language.h | ||
| lexer.c | ||
| lexer.h | ||
| linux_kernel_helpers.c | ||
| linux_kernel.c | ||
| linux_kernel.h | ||
| Makefile.am | ||
| memory_reader.c | ||
| memory_reader.h | ||
| object_index.c | ||
| object_index.h | ||
| object.c | ||
| object.h | ||
| path.c | ||
| platform.c | ||
| platform.h | ||
| program.c | ||
| program.h | ||
| read.h | ||
| serialize.c | ||
| serialize.h | ||
| siphash.h | ||
| splay_tree.c | ||
| stack_trace.c | ||
| string_builder.c | ||
| string_builder.h | ||
| symbol.c | ||
| symbol.h | ||
| type.c | ||
| type.h | ||
| util.h | ||
| vector.c | ||
| vector.h | ||