There are a couple of reasons that it was the wrong choice to have a
bit_offset for value objects:
1. When we store a buffer with a bit_offset, we're storing useless
padding bits.
2. bit_offset describes a location, or in other words, part of an
address. This makes sense for references, but not for values, which
are just a bag of bytes.
Get rid of union drgn_value.bit_offset in libdrgn, make
Object.bit_offset None for value objects, and disallow passing
bit_offset to the Object() constructor when creating a value. bit_offset
can still be passed when creating an object from a buffer, but we'll
shift the bytes down as necessary to store the value with no offset.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
THREAD_SIZE is still broken and I haven't looked into the root cause
(see commit 95be142d17 ("tests: disable THREAD_SIZE test")). We don't
need it anymore anyways, so let's remove it entirely.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
On old kernels, we set the initial frame as containing only rbp and let
libdwfl unwind it assuming frame pointers from there. This means that
the initial frame has a garbage rip. Follow the frame pointer and set
the previous rbp and return address ourselves instead.
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'd like to use the name drgn_object_kind to distinguish between values
and references. "Encoding" is more accurate than "kind", anyways.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
There are several places where we'd like to enforce that every
enumeration is handled in a switch. Add SWITCH_ENUM() and
SWITCH_ENUM_DEFAULT() macros for that and use them.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
If virtual address translation isn't implemented for the target
architecture, then we shouldn't add the page table memory reader. If we
do, we get a DRGN_ERROR_INVALID_ARGUMENT error from
linux_helper_read_vm() instead of a DRGN_ERROR_FAULT error as expected.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
If the DWARF index encounters any error while parsing, it returns an
error saying only "debug information is truncated", which makes it hard
to track down parsing errors. The kmod index parser silently swallows
errors. For both, replace the mread functions with a higher-level
binary_buffer interface that can include more information including the
location of the error. For example:
/tmp/mybinary: .debug_info+0x4: expected at least 56 bytes, have 55
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Back in commit 9ce9094ee0 ("libdrgn: dwarf_index: don't copy sections
into each CU"), I changed the sections to be individual members. The
next change will be easier if they're in an array.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
There are several places where we manually pass around the string name
of a tag so it can be used for error messages. Do it programatically
instead.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Linux v5.8 changed the module section structure, so we need to get the
section name differently.
Closes#73.
Reported-by: Serapheim Dimitropoulos <serapheim@delphix.com>
Signed-off-by: Omar Sandoval <osandov@osandov.com>
If cache_kernel_module_sections() in report_loaded_kernel_module()
fails, we continue to the next iteration without advancing to the next
kernel module. Then, we fail on that same kernel module and repeat. Make
sure that we go to the next kernel module.
Fixes: 423d2cd500 ("libdrgn: dwarf_index: rework file reporting")
Reported-by: Serapheim Dimitropoulos <serapheim@delphix.com>
Signed-off-by: Omar Sandoval <osandov@osandov.com>
We're freeing path and then using it to report an error.
This has some weird knock-on effects. Since we freed the path, the error
message contains garbage. So, PyErr_SetString() can't decode it as a
UTF-8 string. The end result is a MissingDebugInfoError with no message.
Fix it by creating the error before freeing the path.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
We use /proc/modules and /sys/module to find loaded kernel modules for
the running kernel instead of walking the module list in the core dump
as an optimization. To make it easier to test the core dump path, add an
environment variable to disable the optimization.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
The next commit will allow using the offline path for the live kernel,
so the offline naming won't make much sense. Fold the offline path into
the top-level functions, and make the live path an escape hatch. Also
add some comments and improve naming for the file and directory handles
and update the coding style.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
These were added in commit e5874ad18a ("libdrgn: use libdwfl"), but
they have never been used. Remove them.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Use *_hash_pair() for hash functions that do the full double hashing and
return a struct hash_pair and hash_*() for other hashing utility
functions. Also change some of the equality function names to be more
symmetric and improve the documentation.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
min() and max() from the Linux kernel go through the trouble of
resulting in a constant expression if the arguments are constant
expressions, but they can't be used outside of a function due to their
use of ({ }). This means that they can't be used for, e.g., enumerators
or global arrays. Let's simplify min() and max() and instead add
explicit min_iconst() and max_iconst() macros that can be used
everywhere that an integer constant expression is required. We can then
use it in hash_table.h. While we're here, let's split these into their
own header file and document them better.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
drgn_type_members_eq() skips comparing the types of anonymous members.
Fix that and add a test for it.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
The Doxygen documentation for libdrgn has bit-rotted over time. Bring
back the Internal module, clean up a few renamed members and parameters,
and fix broken parsing caused by the generic definition macros.
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>
The elfutils header files should be treated as if they were in the
standard location, so use -isystem instead of -I.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
If we create a pending CU for a namespace, then add more CUs to the
index, the CU might get reallocated, resulting in a use after free. Fix
it by storing the index of the CU instead of the pointer.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Debugging information tracking is currently in two places: drgn_program
finds debugging information, and drgn_dwarf_index stores it. Both of
these responsibilities make more sense as part of drgn_debug_info, so
let's move them there. This prepares us to track extra debugging
information that isn't pertinent to indexing.
This also reworks a couple of details of loading debugging information:
- drgn_dwarf_module and drgn_dwfl_module_userdata are consolidated into
a single structure, drgn_debug_info_module.
- The first pass of DWARF indexing now happens in parallel with reading
compilation units (by using OpenMP tasks).
Signed-off-by: Omar Sandoval <osandov@osandov.com>
DWARF represents namespaces with DW_TAG_namespace DIEs. Add these to the
DWARF index, with each namespace being its own sub-index. We only index
the namespace itself when it is first accessed, which should help with
startup time and simplifies tracking.
Signed-off-by: Jay Kamat <jaygkamat@gmail.com>
In order to index namespaces lazily, we need the CU structures. Rename
struct compilation_unit to the less generic struct drgn_dwarf_index_cu
and keep the CUs in a vector in the dindex.
Signed-off-by: Jay Kamat <jaygkamat@gmail.com>
For namespace support, we will want to access the struct
drgn_dwarf_index_die for namespaces instead of the Dwarf_Die. Split
drgn_dwarf_index_get_die() out of drgn_dwarf_index_iterator_next().
Signed-off-by: Omar Sandoval <osandov@osandov.com>
There are a couple of related ways that we can cause undefined behavior
when parsing a malformed DWARF or depmod index file:
1. There are several places where we increment the cursor to skip past
some data. It is undefined behavior if the result points out of
bounds of the data, even if we don't attempt to dereference it.
2. read_in_bounds() checks that ptr <= end. This pointer comparison is
only defined if ptr and end both point to elements of the same array
object or one past the last element. If ptr has gone past end, then
this comparison is likely undefined anyways.
Fix it by adding a helper to skip past data with bounds checking. Then,
all of the helpers can assume that ptr <= end and maintain that
invariant. while we're here and auditing all of the call sites, let's
clean up the API and rename it from read_foo() to the less generic
mread_foo().
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Now that we can handle a DW_AT_specification that references another
compilation unit, add support for DW_FORM_ref_addr.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
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>
It's very unlikely that we'll ever index more than 4 billion DIEs in a
single shard, so we can shrink the index a bit by using uint32_t
indices (and uint8_t tag).
Signed-off-by: Omar Sandoval <osandov@osandov.com>
I originally copied the sections into each compilation unit to avoid a
pointer indirection, but performance-wise it's a wash, so we might as
well save the memory. This will be more important when we keep the CUs
after indexing.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
In read_cus(), the master thread can use the final CUs vector directly
and the rest of the threads can merge their private vectors in. This
consistently shaves a few milliseconds off of startup.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
We currently assume that if DW_AT_declaration is present, it is true.
This seems to be true in practice, and I see no reason to ever use
DW_FORM_flag with a value of zero. There's no performance hit to handle
it, though, so we might as well.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
As a small simplification, we can take commit 9bb2ccecb7 ("Enable
DWARF indexing to work with partial units") further and not look at the
tag of the top-level DIE at all.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
