Most places that call these check has_platform and return an error, and
those that don't can live with the extra check.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Program::objects is used to store references to objects that must stay
alive while the Program is alive. It is currently a PyDict where the
keys are the object addresses as PyLong and the values are the objects
themselves. This has two problems:
1. Allocating the key as a full object is obviously wasteful.
2. PyDict doesn't have an API for reserving capacity ahead of time,
which we want for an upcoming change.
Both of these are easily fixed by using our own hash table.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
drgn_object_init() is available in drgh.h file and seems to a required
call before calling drgn_program_find_object().
Without this, trying to call drgn_object_init() from an external C
application results in undefined reference.
Signed-off-by: Aditya Sarwade <asarwade@fb.com>
Now that drgndoc can handle overloads and we have the IntegerLike and
Path aliases, we can add type annotations to all helpers. There are also
a couple of functional changes that snuck in here to make annotating
easier.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Rather than duplicating Union[str, bytes, os.PathLike] everywhere, add
an alias. Also make it explicitly os.PathLike[str] or os.PathLike[bytes]
to get rid of some mypy --strict errors.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Lots if interfaces in drgn transparently turn an integer Object into an
int by using __index__(), so add an IntegerLike protocol for this and
use it everywhere applicable.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Make the KASLR offset available to Python in a new
drgn.helpers.linux.boot module, and move pgtable_l5_enabled() there,
too.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Clean up the coding style of the remaining few places that the last
couple of changes didn't rewrite.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
The folly F14 implementation provides 3 storage policies: value, node,
and vector. The default F14FastMap/F14FastSet chooses between the value
and vector policies based on the value size.
We currently only implement the value policy, as the node policy is easy
to emulate and the vector policy would've added more complexity. This
adds support for the vector policy (adding even more C abuse :) and
automatically chooses the policy the same way as folly. It'd be easy to
add a way to choose the policy if needed.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
The only major change to the folly F14 implementation since I originally
ported it is commit 3d169f4365cf ("memory savings for F14 tables with
explicit reserve()"). That is a small improvement for small tables and a
large improvement for vector tables, which are about to be added.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
posix_memalign() doesn't have the restriction that the size must be a
multiple of the alignment like aligned_alloc() does in C11.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Compile-time constants have DW_AT_const_value instead of DW_AT_location.
We can translate those to a value object.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Really it's more of a test program than an example program. It's useful
for benchmarking, testing with valgrind, etc. It's not built by default,
but it can be built manually with:
$ make -C build/temp.* examples/load_debug_info
And run with:
$ ./build/temp.*/examples/load_debug_info
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Commit eea5422546 ("libdrgn: make Linux kernel stack unwinding more
robust") overlooked that if the task is running in userspace, the stack
pointer in PRSTATUS obviously won't match the kernel stack pointer.
Let's bite the bullet and use the PID. If the race shows up in practice,
we can try to come up with another workaround.
I once tried to implement a generic arithmetic right shift macro without
relying on any implementation-defined behavior, but this turned out to
be really hard. drgn is fairly tied to GCC and GCC-compatible compilers
(like Clang), so let's just assume GCC's model [1]: modular conversion
to signed types, two's complement signed bitwise operators, and sign
extension for signed right shift.
1: https://gcc.gnu.org/onlinedocs/gcc/Integers-implementation.html
Declaring a local vector or hash table and separately initializing it
with vector_init()/hash_table_init() is annoying. Add macros that can be
used as initializers.
This exposes several places where the C89 style of placing all
declarations at the beginning of a block is awkward. I adopted this
style from the Linux kernel, which uses C89 and thus requires this
style. I'm now convinced that it's usually nicer to declare variables
where they're used. So let's officially adopt the style of mixing
declarations and code (and ditch the blank line after declarations) and
update the functions touched by this change.
We were forgetting to mask away the extra bits. There are two places
that we use the tag without converting it to a uint8_t:
hash_table_probe_delta(), which is mostly benign since we mask it by the
chunk mask anyways; and table_chunk_match() without SSE 2, which
completely breaks.
While we're here, let's align the comments better.
After thinking about it some more, I realized that "libdwfl: simplify
activation frame logic" breaks the case where during unwinding someone
queries isactivation for reasons other than knowing whether to decrement
program counter. Revert the patch and refactor "libdwfl: add interface
for getting Dwfl_Module and Dwarf_Frame for Dwfl_Frame" to handle it
differently.
Based on:
c95081596 size: Also obey radix printing for bsd format.
With the following patches:
configure: Add --disable-programs
configure: Add --disable-shared
libdwfl: add interface for attaching to/detaching from threads
libdwfl: export __libdwfl_frame_reg_get as dwfl_frame_register
libdwfl: add interface for getting Dwfl_Module and Dwarf_Frame for Dwfl_Frame
libdwfl: add interface for evaluating DWARF expressions in a frame
drgn has a couple of issues unwinding stack traces for kernel core
dumps:
1. It can't unwind the stack for the idle task (PID 0), which commonly
appears in core dumps.
2. It uses the PID in PRSTATUS, which is racy and can't actually be
trusted.
The solution for both of these is to look up the PRSTATUS note by CPU
instead of PID.
For the live kernel, drgn refuses to unwind the stack of tasks in the
"R" state. However, the "R" state is running *or runnable*, so in the
latter case, we can still unwind the stack. The solution for this is to
look at on_cpu for the task instead of the state.
We currently unwind from pt_regs and NT_PRSTATUS using an array of
register definitions. It's more flexible and more efficient to do this
with an architecture-specific callback. For x86-64, this change also
makes us depend on the binary layout rather than member names of struct
pt_regs, but that shouldn't matter unless people are defining their own,
weird struct pt_regs.
The model has always been that drgn Objects are immutable, but for some
reason I went through the trouble of allowing __init__() to reinitialize
an already initialized Object. Instead, let's fully initialize the
Object in __new__() and get rid of __init__().
It's annoying to have to do value= when creating objects, especially in
interactive mode. Let's allow passing in the value positionally so that
`Object(prog, "int", value=0)` becomes `Object(prog, "int", 0)`. It's
clear enough that this is creating an int with value 0.
drgn was originally my side project, but for awhile now it's also been
my work project. Update the copyright headers to reflect this, and add a
copyright header to various files that were missing it.
For functions that call a noreturn function, the compiler may omit code
after the call instruction. This means that the return address may not
lie in the caller's symbol. dwfl_frame_pc() returns whether a frame is
an "activation", i.e., its program counter is guaranteed to lie within
the caller. This is only the case for the initial frame, frames
interrupted by a signal, and the signal trampoline frame. For everything
else, we need to decrement the program counter before doing any lookups.
Rebase on master and fix dwfl_frame_module/dwfl_frame_dwarf_frame to
decrement the program counter when necessary.
Based on:
a8493c12a libdw: Skip imported compiler_units in libdw_visit_scopes walking DIE tree
With the following patches:
configure: Add --disable-programs
configure: Add --disable-shared
libdwfl: simplify activation frame logic
libdwfl: add interface for attaching to/detaching from threads
libdwfl: add interface for getting Dwfl_Module and Dwarf_Frame for Dwfl_Frame
libdwfl: export __libdwfl_frame_reg_get as dwfl_frame_register
libdwfl: add interface for evaluating DWARF expressions in a frame
Now that we can walk page tables, we can use it in a memory reader that
reads kernel memory via the kernel page table. This means that we don't
need libkdumpfile for ELF vmcores anymore (although I'll keep the
functionality around until this code has been validated more).
I originally wanted to avoid depending on another vmcoreinfo field, but
an the next change is going to depend on swapper_pg_dir in vmcoreinfo
anyways, and it ends up being simpler to use it.
There are a few big use cases for this in drgn:
* Helpers for accessing memory in the virtual address space of userspace
tasks.
* Removing the libkdumpfile dependency for vmcores.
* Handling gaps in the virtual address space of /proc/kcore (cf. #27).
I dragged my feet on implementing this because I thought it would be
more complicated, but the page table layout on x86-64 isn't too bad.
This commit implements page table walking using a page table iterator
abstraction. The first thing we'll add on top of this will be a helper
for reading memory from a virtual address space, but in the future it'd
also be possible to export the page table iterator directly.
UNARY_OP_SIGNED_2C() uses a union of int64_t and uint64_t to avoid
signed integer overflow... except that there's a typo and the uint64_t
is actually an int64_t. Fix it and add a test that would catch it with
-fsanitize=undefined.
internal.h includes both drgn-specific helpers and generic utility
functions. Split the latter into their own util.h header and use it
instead of internal.h in the generic data structure code. This makes it
easier to copy the data structures into other projects/test programs.
Program_load_debug_info() is the last user of the
resize_array()/realloc_array() utility functions. We can clean it up by
using a vector and finally get rid of those functions.
This also happens to fix three bugs in Program_load_debug_info(): we
weren't setting a Python exception if we couldn't allocate the path_args
array, we weren't zeroing path_args after resizing the array, and we
weren't freeing the path_args array. Shame on whoever wrote this.
DRGN_UNREACHABLE() currently expands to abort(), but assert() provides
more information. If NDEBUG is defined, we can use
__builtin_unreachable() instead.
DRGN_UNREACHABLE() isn't drgn-specific, so this renames it to
UNREACHABLE(). It's also not really related to errors, so this moves it
to internal.h.
Before Linux v4.11, /proc/kcore didn't have valid physical addresses, so
it's currently not possible to read from physical memory on old kernels.
However, if we can figure out the address of the direct mapping, then we
can determine the corresponding physical addresses for the segments and
add them.
We treat core dumps with all zero p_paddrs as not having valid physical
addresses. However, it is theoretically possible for a kernel core dump
to only have one segment which legitimately has a p_paddr of 0 (e.g., if
it only has a segment for the direct mapping, although note that this
isn't currently possible on x86, as Linux on x86 reserves PFN 0 for the
BIOS [1]).
If the core dump has a VMCOREINFO note, then it is either a vmcore,
which has valid physical addresses, or it is /proc/kcore with Linux
kernel commit 23c85094fe18 ("proc/kcore: add vmcoreinfo note to
/proc/kcore") (in v4.19), so it must also have Linux kernel commit
464920104bf7 ("/proc/kcore: update physical address for kcore ram and
text") (in v4.11) (ignoring the possibility of a franken-kernel which
backported the former but not the latter). Therefore, treat core dumps
with a VMCOREINFO note as having valid physical addresses.
1: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x86/kernel/setup.c?h=v5.6#n678
Even on 32-bit architectures, physical addresses can be 64 bits (e.g.,
x86 with PAE). It's unlikely that the vmcoreinfo note would be in such
an address, but let's always parse it as a uint64_t just to be safe.
I've found that I do this manually a lot (e.g., when digging through a
task's stack). Add shortcuts for reading unsigned integers and a note
for how to manually read other formats.
DrgnObject_getattro() uses PyObject_GenericGetAttr() and catches the
AttributeError raised if the name is not an attribute of the Object
class. If the member is found, we then destroy the AttributeError.
Raising an exception only to destroy it is obviously wasteful. Luckily,
as of Python 3.7, the lower-level _PyObject_GenericGetAttrWithDict() can
suppress the AttributeError; we can raise it ourselves if we need it. In
my microbenchmarks, this makes Object.__getattribute__() at least twice
as fast when the member exists.
This also fixes a drgn_error leak.
Loading debuginfo from a kernel with separate or re-combined debuginfo
results in the following failure:
Traceback (most recent call last):
File "/home/jeffm/.local/bin/drgn", line 11, in <module>
load_entry_point('drgn==0.0.3+39.gbf05d9bf', 'console_scripts', 'drgn')()
File "/home/jeffm/.local/lib/python3.6/site-packages/drgn-0.0.3+39.gbf05d9bf-py3.6-linux-x86_64.egg/drgn/internal/cli.py", line 121, in main
prog.load_debug_info(args.symbols, **args.default_symbols)
Exception: invalid DW_AT_decl_file 10
A typical kernel build results in DWARF information with
DW_TAG_compile_unit tags but the objcopy --only-keep-debug and eu-unstrip
commands use DW_TAG_partial_unit tags. The DWARF indexer only handles
the former, so the file table isn't populated and we get the exception.
Fortunately, the two are more or less interchangeable. (See
http://dwarfstd.org/doc/Dwarf3.pdf, section E.2.3). Accepting both for
indexing compile units results in a working session.
compound_initializer_init_next() saves a pointer to the compound
initializer stack and uses it after appending to the stack, which may
have reallocated the stack.
For C++ support, we need to add an array of template parameters to
struct drgn_type. struct drgn_type already has arrays for members,
enumerators, and parameters embedded at the end of the structure,
because no type needs more than one of those. However, struct, union,
and class types may need members and template parameters. We could add a
separate array of templates, but then it gets confusing having two
methods of storing arrays in struct drgn_type. Let's make these arrays
separate instead of embedding them.
Similarly to PAGE_OFFSET, vmemmap makes more sense as part of the Linux
kernel object finder than an internal helper.
While we're here, let's fix the definition for 5-level page tables. This
only matters for kernels with commit 77ef56e4f0fb ("x86: Enable 5-level
paging support via CONFIG_X86_5LEVEL=y") but without eedb92abb9bb
("x86/mm: Make virtual memory layout dynamic for CONFIG_X86_5LEVEL=y")
(namely, v4.14, v4.15, and v4.16); since v4.17, 5-level page table
support enables KASLR.
The internal _page_offset() helper gets the value of PAGE_OFFSET, but
the fallback when KASLR is disabled has been out of date since Linux
v4.20 and never handled 5-level page tables. Additionally, it makes more
sense as part of the Linux kernel (formerly vmcoreinfo) object finder so
that it's cleanly accessible outside of drgn internals.
The configure script allows the user to not use any openmp
implementation but dwarf_index.c uses the locking APIs unconditionally.
This compiles but fails at runtime.
Adding simple stubs for the locking API. This is useful when debugging
crashes in dwarf indexing during development.
elfutils 0.179 was just released, and it includes my fix for vmcores
with >= 2^16 phdrs.
Based on:
3a7728808 Prepare for 0.179
With the following patches:
configure: Add --disable-programs
configure: Add --disable-shared
libdwfl: add interface for attaching to/detaching from threads
libdwfl: add interface for getting Dwfl_Module and Dwarf_Frame for Dwfl_Frame
libdwfl: export __libdwfl_frame_reg_get as dwfl_frame_register
libdwfl: add interface for evaluating DWARF expressions in a frame
Jay reported that the default language detection was happening too early
and not finding "main". We need to make sure to do it after the DWARF
index is actually populated. The problem with that is that it makes
error reporting much harder, as we don't want to return a fatal error
from drgn_program_set_language_from_main() if we actually succeeded in
loading debug info. That means we probably need to ignore errors in
drgn_program_set_language_from_main(). To reduce the surface area where
we'd be failing, let's get the language directly from the DWARF index.
This also allows us to avoid setting the language if it's actually
unknown (information which is lost by the time we convert it to a
drgn_object in the current code).
Currently, drgn_language_from_die() returns the default language when it
encounters an unknown DW_LANG because the dwarf_info_cache always wants
a language. The next change will want to detect the unknown language
case, so make drgn_language_from_die() return NULL if the language is
unknown, move it to language.c, and fold drgn_language_from_dw_lang()
into it.
We need to keep the Program alive for its types to stay valid, not just
the objects the Program has pinned. (I have no idea why I changed this
in commit 565e0343ef ("libdrgn: make symbol index pluggable with
callbacks").)
For operations where we don't have a type available, we currently fall
back to C. Instead, we should guess the language of the program and use
that as the default. The heurisitic implemented here gets the language
of the CU containing "main" (except for the Linux kernel, which is
always C). In the future, we should allow manually overriding the
automatically determined language.
For types obtained from DWARF, we determine it from the language of the
CU. For other types, it can be specified manually or fall back to the
default (C). Then, we can use the language for operations where the type
is available.
This way, languages can be identified by an index, which will be useful
for adding Python bindings for drgn_language and for adding a language
field to drgn_type.
I've been wanting to add type hints for the _drgn C extension for
awhile. The main blocker was that there is a large overlap between the
documentation (in docs/api_reference.rst) and the stub file, and I
really didn't want to duplicate the information. Therefore, it was a
requirement that the the documentation could be generated from the stub
file, or vice versa. Unfortunately, none of the existing tools that I
could find supported this very well. So, I bit the bullet and wrote my
own Sphinx extension that uses the stub file as the source of truth (and
subsumes my old autopackage extension and gen_docstrings script).
The stub file is probably incomplete/inaccurate in places, but this
should be a good starting point to improve on.
Closes#22.
I thought I'd be able to avoid adding a separate API for register values
and reuse dwfl_frame_eval_expr(), but this doesn't work if the frame is
missing debug information but has known register values (e.g., if the
program crashed with an invalid instruction pointer).
Rebase on master, add the improved
dwfl_frame_module/dwfl_frame_dwarf_frame patch, and add the
dwfl_frame_register patch.
Based on:
889edd912 PR25365: debuginfod-client: restrict cleanup to client-pattern files
With the following patches:
configure: Add --disable-programs
configure: Add --disable-shared
libdwfl: add interface for attaching to/detaching from threads
libdwfl: add interface for getting Dwfl_Module and Dwarf_Frame for Dwfl_Frame
libdwfl: export __libdwfl_frame_reg_get as dwfl_frame_register
libdwfl: add interface for evaluating DWARF expressions in a frame
UTS_RELEASE is currently only accessible once debug info is loaded with
prog.load_debug_info(main=True). This makes it difficult to get the
release, find the appropriate vmlinux, then load the found vmlinux. We
can add vmcoreinfo_object_find as part of set_core_dump(), which makes
it possible to do the following:
prog = drgn.Program()
prog.set_core_dump(core_dump_path)
release = prog['UTS_RELEASE'].string_()
vmlinux_path = find_vmlinux(release)
prog.load_debug_info([vmlinux_path])
The only downside is that this ends up using the default definition of
char rather than what we would get from the debug info, but that
shouldn't be a big problem.
The osrelease is accessible via init_uts_ns.name.release, but we can
also get it straight out of vmcoreinfo, which will be useful for the
next change. UTS_RELEASE is the name of the macro defined in the kernel.
This continues the conversion from the last commit. Members and
parameters are basically the same, so we can do them together. Unlike
enumerators, these don't make sense to unpack or access as sequences.
Currently, type members, enumerators, and parameters are all represented
by tuples in the Python bindings. This is awkward to document and
implement. Instead, let's replace these tuples with proper types,
starting with the easiest one, TypeEnumerator. This one still makes
sense to treat as a sequence so that it can be unpacked as (name,
value).
Currently, we print:
>>> prog.symbol(prog['init_task'])
Traceback (most recent call last):
File "<console>", line 1, in <module>
TypeError: cannot convert 'struct task_struct' to index
It's not obvious what it means to convert to an index. Instead, let's
use the error message raised by operator.index():
TypeError: 'struct task_struct' object cannot be interpreted as an integer
Decouple some of the responsibilities of FaultError to
OutOfBoundsError so consumers can differentiate between
invalid memory accesses and running out of bounds in
drgn Objects which may be based on valid memory address.
At Facebook, we link OpenMP code with libomp instead of libgomp. We have
an internal patch to drgn to do this, as it can't be done by setting
CFLAGS/LDFLAGS. Let's add a way to specify the OpenMP library at
configure time so that we can drop the internal patch.
When investigating a reported bug, it's important to know which exact
version of drgn is being used. Let's include the git revision in the
version printed by the CLI in PEP440 format. This commit will also serve
as the 0.0.1 release.
Currently the drgn version number is defined in drgn.h.in, and configure
and setup.py both parse it out of there. However, now that we're
generating drgn.h anyways, it's easier to make configure.ac the source
of truth.
When we're checking whether the element that we formatted on one line
would fit on the previous line, we check whether the previous line is
empty with remaining_columns == start_columns. This is never true, as
remaining_columns is always set to start_columns - 1 at most, and it
only decreases from there until we start a new line.
drgn_object_truthiness() is a misnomer, as truthiness is a
language-specific concept. Instead, invert the return value and rename
it to drgn_object_is_zero(), which more accurately conveys the meaning.
Instead of having two internal variants (drgn_find_symbol_internal() and
drgn_program_find_symbol_in_module()), combine them into the former and
add a separate drgn_error_symbol_not_found() for translating the static
error to the user-facing one. This makes things more flexible for the
next change.
We'd like to have more control over how objects are formatted. I
considered defining a custom string format specification syntax, but
that's not easily discoverable. Instead, let's get rid of the current
format specification support and replace it with a normal method.
In preparation for making drgn_pretty_print_object() more flexible
(i.e., not always "pretty"), rename it to drgn_format_object(). For
consistency, let's rename drgn_pretty_print_type_name(),
drgn_pretty_print_type(), and drgn_pretty_print_stack_trace(), too.
Commit f327552229 ("libdrgn: add strstartswith()") flipped the test
for a name entry in modinfo. This introduced a regression resulting in
kernel modules not loading at the right offset. This patch fixes the
regression.
The previous commit was the real fix for the failed symbol lookups. On
the bright side, the build fixes were merged, so we can rebase on master
and drop those.
Based on:
277c2c54f libcpu: Compile i386_lex.c with -Wno-implicit-fallthrough
With the following patches:
configure: Add --disable-programs
configure: Add --disable-shared
libdwfl: add interface for attaching to/detaching from threads
libdwfl: cache Dwfl_Module and Dwarf_Frame for Dwfl_Frame
libdwfl: add interface for evaluating DWARF expressions in a frame
It turns out this wasn't a problem with dwfl_addrmodule() at all; the
real problem is that .init sections are freed once the module is loaded
but we're still considering them for the address range we pass to
dwfl_report_module(). Ignore those sections entirely (by omitting them
from the section name to section index map). While we're here, let's not
bother inserting non-SHF_ALLOC sections in the map.
This fixes the issue that Program.symbol() sometimes fails for kernel
module symbols.
Based on:
2c7c4037 elfutils.spec.in: Sync with fedora spec, remove rhel/fedora specifics.
With the following patches:
configure: Add --disable-programs
configure: Add --disable-shared
configure: Fix -D_FORTIFY_SOURCE=2 check when CFLAGS contains -Wno-error
libcpu: compile i386_lex.c with -Wno-implicit-fallthrough
libdwfl: add interface for attaching to/detaching from threads
libdwfl: cache Dwfl_Module and Dwarf_Frame for Dwfl_Frame
libdwfl: add interface for evaluating DWARF expressions in a frame
libdwfl: return error from __libdwfl_relocate_value for unloaded sections
libdwfl: remove broken coalescing logic in dwfl_report_segment
libdwfl: store module lookup table separately from segments
libdwfl: use sections of relocatable files for dwfl_addrmodule
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.
In commit 55a9700435 ("libdrgn: python: accept integer-like arguments
in more places"), I converted Program_symbol to use index_converter but
forgot to initialize the struct index_arg. Then, in commit c243daed59
("Translate find_task() helper (and dependencies) to C"), I added a
bunch more cases of uninitialized struct index_arg. If
index_arg.allow_none gets a non-zero garbage value, then this can end up
allowing None through when it shouldn't. Furthermore, since commit
2561226918 ("libdrgn: python: add signed integer support to
index_converter"), if index_arg.is_signed gets a non-zero garbage value,
then this will try to get a signed integer when we're expecting an
unsigned integer, which can blow up for values >= 2**63 (like kernel
symbols). Fix it by initializing struct index_arg everywhere.
Fixes#30.
Rebase on 0.178. The only additional change needed is to pass
--disable-debuginfod to configure.
Based on:
2c7c4037 elfutils.spec.in: Sync with fedora spec, remove rhel/fedora specifics.
With the following patches:
configure: Add --disable-programs
configure: Add --disable-shared
configure: Fix -D_FORTIFY_SOURCE=2 check when CFLAGS contains -Wno-error
libcpu: compile i386_lex.c with -Wno-implicit-fallthrough
libdwfl: add interface for attaching to/detaching from threads
libdwfl: cache Dwfl_Module and Dwarf_Frame for Dwfl_Frame
libdwfl: add interface for evaluating DWARF expressions in a frame
Matt Ahrens reported that comparing two types would sometimes end up in
a seemingly infinite loop, which he discovered was because we repeat
comparisons of types as long as they're not in a cycle. Fix it by
caching all comparisons during a call.
Some tests (e.g., tests.test_object.TestSpecialMethods.test_round) are
printing:
DeprecationWarning: an integer is required (got type float). Implicit
conversion to integers using __int__ is deprecated, and may be removed
in a future version of Python.
See https://bugs.python.org/issue36048. This is coming from calls like:
Object(prog, 'int', value=1.5)
We actually want the truncating behavior, so explicitly call
PyNumber_Long().
If we only want debugging information for vmlinux and not kernel
modules, it'd be nice to only load the former. This adds a load_main
parameter to drgn_program_load_debug_info() which specifies just that.
For now, it's only implemented for the Linux kernel. While we're here,
let's make the paths parameter optional for the Python bindings.
This implements the first step at supporting C++: class types. In
particular, this adds a new drgn_type_kind, DRGN_TYPE_CLASS, and support
for parsing DW_TAG_class_type from DWARF. Although classes are not valid
in C, this adds support for pretty printing them, for completeness.
Python 3.8 replaced the unused void *tp_print field with Py_ssize_t
tp_vectorcall_offset, so with -Werror we get "error: initialization of
‘long int’ from ‘void *’ makes integer from pointer without a cast".
Let's just use designated initializers.
We currently don't check that the task we're unwinding is actually
blocked, which means that linux_kernel_set_initial_registers_x86_64()
will get garbage from the stack and we'll return a nonsense stack trace.
Let's avoid this by checking that the task isn't running if we didn't
find a NT_PRSTATUS note.
Add a helper to get the state of a task (e.g., 'R', 'S', 'D'). This will
be used to make sure that a task is not running when getting a stack
trace, so implement it in libdrgn.
When debugging the Linux kernel, it's inconvenient to have to get the
task_struct of a thread in order to get its stack trace. This adds
support for looking it up solely by PID. In that case, we do the
find_task() inside of libdrgn. This also gives us stack trace support
for userspace core dumps almost for free since we already added support
for NT_PRSTATUS.
vmcores include a NT_PRSTATUS note for each CPU containing the PID of
the task running on that CPU at the time of the crash and its registers.
We can use that to unwind the stack of the crashed tasks.
Currently, we close the Elf handle in drgn_set_core_dump() after we're
done with it. However, we need the Elf handle in
userspace_report_debug_info(), so we reopen it temporarily. We will also
need it to support getting stack traces from core dumps, so we might as
well keep it open. Note that we keep it even if we're using libkdumpfile
because libkdumpfile doesn't seem to have an API to access ELF notes.
We'd like to be able to look up tasks by PID from libdrgn, but those
helpers are written in Python. Translate them to C and add some thin
bindings so we can use the same implementation from Python.
There are some cases where we want to read an integer regardless of its
signedness, so drgn_object_read_signed() and drgn_object_read_unsigned()
are cumbersome to use, and drgn_object_read_value() is too permissive.
Currently, the only information available from a stack frame is the
program counter. Eventually, we'd like to add support for getting
arguments and local variables, but that will require more work. In the
mean time, we can at least get the values of other registers. A
determined user can read the assembly for the code they're debugging and
derive the values of variables from the registers.
Rebase the existing patches and add the patches which extend the libdwfl
stack frame interface.
Based on:
47780c9e elflint, readelf: enhance error diagnostics
With the following patches:
configure: Add --disable-programs
configure: Add --disable-shared
configure: Fix -D_FORTIFY_SOURCE=2 check when CFLAGS contains -Wno-error
libcpu: compile i386_lex.c with -Wno-implicit-fallthrough
libdwfl: don't bother freeing frames outside of dwfl_thread_getframes
libdwfl: only use thread->unwound for initial frame
libdwfl: add interface for attaching to/detaching from threads
libdwfl: cache Dwfl_Module and Dwarf_Frame for Dwfl_Frame
libdwfl: add interface for evaluating DWARF expressions in a frame
In order to retrieve registers from stack traces, we need to know what
registers are defined for a platform. This adds a small DSL for defining
registers for an architecture. The DSL is parsed by an awk script that
generates the necessary tables, lookup functions, and enum definitions.
It's annoying to do obj.type_.size, and that doesn't even work for every
type. Add sizeof() that does the right thing whether it's given a Type
or Object.
For the following source code:
int arr[] = {};
GCC emits the following DWARF:
DWARF section [ 4] '.debug_info' at offset 0x40:
[Offset]
Compilation unit at offset 0:
Version: 4, Abbreviation section offset: 0, Address size: 8, Offset size: 4
[ b] compile_unit abbrev: 1
producer (strp) "GNU C17 9.2.0 -mtune=generic -march=x86-64 -g"
language (data1) C99 (12)
name (strp) "test.c"
comp_dir (strp) "/home/osandov"
stmt_list (sec_offset) 0
[ 1d] array_type abbrev: 2
type (ref4) [ 34]
sibling (ref4) [ 2d]
[ 26] subrange_type abbrev: 3
type (ref4) [ 2d]
upper_bound (sdata) -1
[ 2d] base_type abbrev: 4
byte_size (data1) 8
encoding (data1) signed (5)
name (strp) "ssizetype"
[ 34] base_type abbrev: 5
byte_size (data1) 4
encoding (data1) signed (5)
name (string) "int"
[ 3b] variable abbrev: 6
name (string) "arr"
decl_file (data1) test.c (1)
decl_line (data1) 1
decl_column (data1) 5
type (ref4) [ 1d]
external (flag_present) yes
location (exprloc)
[ 0] addr .bss+0 <arr>
Note the DW_AT_upper_bound of -1. We end up parsing this as UINT64_MAX
and returning a "DW_AT_upper_bound is too large" error. It appears that
GCC is simply emitting the array length minus one, so let's treat these
as having a length of zero.
Fixes#19.
There are a few places (e.g., Program.symbol(), Program.read()) where it
makes sense to accept, e.g., a drgn.Object with integer type. Replace
index_arg() with a converter function and use it everywhere that we use
the "K" format for PyArg_Parse*.
I got the error messages for DW_AT_upper_bound and DW_AT_count
backwards; fix it. Also fix the condition for word + 1 overflowing
dimension->length to be word >= UINT64_MAX. (Dwarf_Word is uint64_t so
this is kind of silly, but at least it documents the intent).
Sometimes, I'd like to see all of the missing debug info errors rather
than just the first 5. Allow setting this through the
DRGN_MAX_DEBUG_INFO_ERRORS environment variable.
Make the error message more concise, and reorder the sections so that we
check the most obviously-named section (.debug_info) first and least
important section (.debug_line) last.
Currently, the interface between the DWARF index, libdwfl, and the code
which finds and reports vmlinux/kernel modules is spaghetti. The DWARF
index tracks Dwfl_Modules via their userdata. However, despite
conceptually being owned by the DWARF index, the reporting code reports
the Dwfl_Modules and sets up the userdata. These Dwfl_Modules and
drgn_dwfl_module_userdatas are messy to track and pass between the
layers.
This reworks the architecture so that the DWARF index owns the Dwfl
instance and files are reported to the DWARF index; the DWARF index
takes care of reporting to libdwfl internally. In addition to making the
interface for the reporter much cleaner, this improves a few things as a
side-effect:
- We now deduplicate on build ID in addition to path.
- We now skip searching for vmlinux and/or kernel modules if they were
already indexed.
- We now support compressed ELF files via libdwelf.
- We can now load default debug info at the same time as additional
debug info.
It's undefined behavior to pass NULL to memcmp() even if the length is
zero. See also commit a17215e984 ("libdrgn: dwarf_index: fix memcpy()
undefined behavior").
vmcores don't include program headers for special memory regions like
vmalloc and percpu. Instead, we need to walk the kernel page table to
map those addresses. Luckily, libkdumpfile already does that. So, if
drgn was built with libkdumpfile support, use it for ELF vmcores. Also
add an environment variable to override this behavior.
Closes#15.
I didn't want to use BUILT_SOURCES before because that would break make
$TARGET. But, now that doesn't work anyways because we're using SUBDIRS,
so we might as well use BUILT_SOURCES.
Now that we have the bundled version of elfutils, build it from libdrgn
and link to it. We can also get rid of the elfutils version checks from
the libdrgn code.
Based on:
c950e8a9 config: Fix spec file, add manpages and new GFDL license.
With the following patches:
configure: Add --disable-programs
configure: Add --disable-shared
configure: Fix -D_FORTIFY_SOURCE=2 check when CFLAGS contains -Wno-error
libcpu: compile i386_lex.c with -Wno-implicit-fallthrough
The plan is to stop relying on the distribution's version of elfutils
and instead ship our own. This gives us freedom to assume that we're
using the latest version and even ship our own patches (starting with a
few build system improvements). More details are in
scripts/update-elfutils.sh, which was used to generate this commit.
Currently, we have a special Makefile target to output the files for a
libdrgn source tarball, and we use that for setuptools. However, the
next change is going to import elfutils, and it'd be a pain to add the
same thing for the elfutils sources. Instead, let's just use git
ls-files for everything. The only difference is that source
distributions won't have the autoconf/automake output.
I started with drgn_elf_relocator as a separate interface to parallelize
by relocation. However, the final result is parallelized by file, which
means that it can be done as part of the main read_cus() loop. Get rid
of the elf_relocator interface and do it in dwarf_index.c instead. This
means that if/when libdwfl gets faster at ELF relocations, we can rip
out the relocation code without any other changes.
We're too inconsistent with how we use these for them to be useful (and
it's impossible to distinguish between a format error and some other
error from libelf/libdw/libdwfl), so let's just get rid of them and make
it all DRGN_ERROR_OTHER/Exception.
For now, we only support stack traces for the Linux kernel (at least
v4.9) on x86-64, and we only support getting the program counter and
corresponding function symbol from each stack frame.
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.
Now that we're not overloading the name "symbol", we can define struct
drgn_symbol as a symbol table entry. For now, this is very minimal: it's
just a name, address, and size. We can then add a way to find the symbol
for a given address, drgn_program_find_symbol(). For now, this is only
supported through the actual ELF symbol tables. However, in the future,
we can probably support adding "symbol finders".
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.
Currently, finders indicate a non-fatal lookup error by setting the type
member to NULL. This won't work when we replace the symbol finder with
an object finder (which shouldn't modify the object on failure).
Instead, use a static error for this purpose.
Currently, repr() of structure and union types goes arbitrarily deep
(except for cycles). However, for lots of real-world types, this is
easily deeper than Python's recursion limit, so we can't get a useful
repr() at all:
>>> repr(prog.type('struct task_struct'))
Traceback (most recent call last):
File "<console>", line 1, in <module>
RecursionError: maximum recursion depth exceeded while getting the repr of an object
Instead, only print one level of structure and union types.
We don't need to get the DWARF index at the time we get the Dwfl handle,
so get rid of drgn_program_get_dwarf(), add drgn_program_get_dwfl(), and
create the DWARF index right before we update in a new function,
drgn_program_update_dwarf_index().
After the libdwfl conversion, we apply ELF relocations with libdwfl
instead of our homegrown implementation. However, libdwfl is much slower
at it than the previous implementation. We can work around this by
(again) applying ELF relocations ourselves for architectures that we
care about (x86-64, to start). For other architectures, we can fall back
to libdwfl.
This new implementation of ELF relocation reworks the parallelization to
be per-file rather than per-relocation. The latter was done originally
because before commit 6f16ab09d6 ("libdrgn: only apply ELF relocations
to relocatable files"), we applied relocations to vmlinux, which is much
larger than most kernel modules. Now that we don't do that, it seems to
be slightly faster to parallelize by file.
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.
This converts several open-coded dynamic arrays to the new common vector
implementation:
- drgn_lexer stack
- Array dimension array for DWARF parsing
- drgn_program_read_c_string()
- DWARF index directory name hashes
- DWARF index file name hashes
- DWARF index abbreviation table
- DWARF index shard entries
drgn has enough open-coded dynamic arrays at this point to warrant a
common implementation. Add one inspired by hash_table.h. The API is
pretty minimal. I'll add more to it as the need arises.
There are some cases where we format a path (e.g., with asprintf()) and
keep it around only in case of errors. Add drgn_error_format_os() so we
can just reformat it if we hit the error, which simplifies cleanup.
Since we currently don't parse DWARF macro information, there's no easy
way to get the value PAGE_SIZE and friends in drgn. However, vmcoreinfo
contains the value of PAGE_SIZE, so let's add a special symbol finder
that returns that.
Currently, if we don't get vmcoreinfo from /proc/kcore, and we can't get
it from /sys/kernel/vmcoreinfo, then we manually determine the kernel
release and KASLR offset. This has a couple of issues:
1. We look for vmlinux to determine the KASLR offset, which may not be
in a standard location.
2. We might want to start using other information from vmcoreinfo which
can't be determined as easily.
Instead, we can get the virtual address of vmcoreinfo from
/proc/kallsyms and read it directly from there.
kernel_module_iterator_next() can also fail in
open_loaded_kernel_modules(), so handle it in the same way that we
currently handle kernel_module_iterator_init().
/proc/kcore contains segments which don't have a valid physical address,
which it indicates with a p_paddr of -1. Skip those segments, otherwise
we got an overflow error from the memory reader.
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.
This will be used to track memory segments instead of the array we
currently use. The API is based on the hash table API; it can support
alternative implementations in the future, like red-black trees.
This makes several improvements to the hash table API.
The first two changes make things more general in order to be consistent
with the upcoming binary search tree API:
- Items are renamed to entries.
- Positions are renamed to iterators.
- hash_table_empty() is added.
One change makes the definition API more convenient:
- It is no longer necessary to pass the types into
DEFINE_HASH_{MAP,SET}_FUNCTIONS().
A few changes take some good ideas from the C++ STL:
- hash_table_insert() now fails on duplicates instead of overwriting.
- hash_table_delete_iterator() returns the next iterator.
- hash_table_next() returns an iterator instead of modifying it.
One change reduces memory usage:
- The lower-level DEFINE_HASH_TABLE() is cleaned up and exposed as an
alternative to DEFINE_HASH_MAP() and DEFINE_HASH_SET(). This allows us
to get rid of the duplicated key where a hash map value already embeds
the key (the DWARF index file table) and gets rid of the need to make
a dummy hash set entry to do a search (the pointer and array type
caches).
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.
We need to set the value after we've reinitialized the object, otherwise
drgn_object_deinit() may try to free a buffer that we've already
overwritten. This also adds a test which triggers the crash.
There's a bug that we don't allow comparisons between void * and other
pointer types, so let's fix it by allowing all pointer comparisons
regardless of the referenced type. Although this isn't valid by the C
standard, GCC and Clang both allow it by default (with a warning).
drgn has pretty thorough in-program documentation, but it doesn't have a
nice overview or introduction to the basic concepts. This commit adds
that using Sphinx. In order to avoid documenting everything in two
places, the libdrgn bindings have their docstrings generated from the
API documentation. The alternative would be to use Sphinx's autodoc
extension, but that's not as flexible and would also require building
the extension to build the docs. The documentation for the helpers is
generated using autodoc and a small custom extension.
I went back and forth on using setuptools or autotools for the Python
extension, but I eventually settled on using only setuptools after
fighting to get the two to integrate well. However, setuptools is kind
of crappy; for one, it rebuilds every source file when rebuilding the
extension, which is really annoying for development. automake is a
better designed build system overall, so let's use that for the
extension. We override the build_ext command to build using autotools
and copy things where setuptools expects them.
The declaration file name of a DIE depends on the compilation directory,
which may not always be what the user expects. Instead, make the search
match as long as the full declaration file name ends with the given file
name. This is more convenient and more intuitive.
Running tests with Clang's AddressSanitizer fails with "runtime error:
index 1 out of bounds for type 'struct drgn_type_member [0]'". Zero
length arrays are a GCC extension and aren't buying us much anyways, so
just add a helper function that gets the array payload using pointer
arithmetic.
Older versions of Clang generate a call to __muloti4() for
__builtin_mul_overflow() with mixed signed and unsigned types. However,
Clang doesn't link to compiler-rt by default. Work around it by making
all of our calls to __builtin_mul_overflow() use unsigned types only.
1: https://bugs.llvm.org/show_bug.cgi?id=16404
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.
