Commit 18b12a5c7b ("libdrgn: get .eh_frame from the correct file")
missed this, but it's unlikely to matter in practice.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
These opcodes appear in practice, and we choke on them with an exception
like "unknown DWARF expression opcode 0xf3" or "unknown DWARF expression
opcode 0xa3". In some cases, it'd be possible to recover the entry value
by looking at call site information, but that's pretty involved. For
now, just treat these operations as optimized out so we stop failing
hard.
Closes#233.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
When we get the DIE from the offset with dwarf_offdie(), there's no need
to go back to the offset with dwarf_dieoffset().
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Thierry found that as soon as drgn_module_find_dwarf_scopes() finds any
DIE containing the PC, it walks the entire subtree rooted at that DIE.
However, we only need to look at the immediate children of a DIE
containing the PC. I think this is what I originally intended, but I
failed to reset the children flag to false when the last DIE didn't
contain the PC. Thierry's suggested check of it.dies.size == subtree is
simpler.
This is a massive performance improvement: for a kernel core dump with
10k threads, getting the stack trace of every thread took ~90 seconds
without this fix and ~50 seconds with it.
Let's also add a comment to this very subtle code.
Fixes: d8d4157346 ("libdrgn: debug_info: add drgn_debug_info_module_find_dwarf_scopes()")
Co-authored-by: Thierry Treyer <ttreyer@fb.com>
Signed-off-by: Thierry Treyer <ttreyer@fb.com>
Signed-off-by: Omar Sandoval <osandov@osandov.com>
GCC appears to use data8 at -1 when reporting zero length arrays when
comping c++ code, this patch adds support and a test for that behavior.
dwarf_info.c: Remove check for sdata on quirk for array length == 0
Signed-off-by: Jay Kamat <jaygkamat@gmail.com>
Looking up objects in namespaces is already well-supported by `drgn`.
These changes bring the same to functionality type lookup, so that
`prog.type('struct A::B::C::MyType')` works in an analogous fashion to
`prog['A::B::C::MyVar']`.
Signed-off-by: Kevin Svetlitski <svetlitski@meta.com>
This DWARF tag is used by C++ classes which take a variable number
of template parameters, such as std::variant and std::tuple.
Signed-off-by: Alastair Robertson <ajor@meta.com>
We're currently getting .eh_frame from the debug file. However, since
.eh_frame is an SHF_ALLOC section, it is actually in the loaded file,
and may not be in the debug file. This causes us to fail to unwind in
modules whose debug file was created with objcopy --only-keep-debug
(which is typical for Linux distro debug files).
Fix it by getting .eh_frame from the loaded file. To make this easier,
we split .eh_frame and .debug_frame data into two separate tables. We
also don't bother deduplicating them anymore, since GCC and Clang only
seem to generate one or the other in practice.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Now that we track the debug file ourselves, we can avoid calling libdwfl
in a bunch of places. By tracking the bias ourselves, we can avoid a
bunch more.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
struct drgn_module contains a bunch of information about the debug info
file. Let's pull it out into its own structure, struct drgn_elf_file.
This will be reused for the "main"/"loaded" file in an upcoming change.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
It's confusing that we have a platform both for the program and for each
module. They usually match, but they're not required to. For example,
the user can manually add a file with a different platform just to read
its debug info. Our rule is that if we're parsing anything from the
module, we use the module platform; and otherwise, use the program
platform. There are a couple of places where the platforms must match:
when using call frame information (CFI) or registers. Let's make all of
this more clear in the code (by using the module's platform even when it
must match the program's platform) and in comments. No functional
change.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
If a DW_TAG_pointer_type DIE doesn't specify its size with
DW_AT_byte_size, we currently default to the program's address size.
However, the DWARF we're parsing could be for a platform with a
different address size. It's more correct to use the CU's address size.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
qsort_r is a non-standard glibc extension and turns out to be the only
thing that prevents drgn from working on a musl system. "Fix" the use of
qsort_r by switching it to qsort with a thread local variable for the
parameter.
Tested in a clean chroot install of musl voidlinux.
Signed-off-by: Boris Burkov <boris@bur.io>
The StackFrame's __getitem__() method allows looking up names in the
scope of a stack frame, which is an incredibly useful tool for
debugging. However, the names are not discoverable -- you must already
be looking at the source code or some other source to know what names
can be queried. To fix this, add a locals() method to StackFrame, which
lists names that can be queried in the scope. Since this method is named
locals(), it stops at the function scope and doesn't include globals or
class members.
Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com>
find_dwarf_enumerator() needs to check that the return value of
dwarf_diename() is not NULL before calling strcmp(). This is similar to
commit 330c71b5b5 ("libdrgn: dwarf_info: fix segfault on anonymous
DIEs during scope search"), although I haven't seen this one happen in
practice.
Fixes: bc85767e5f ("libdrgn: support looking up parameters and variables in stack traces")
Signed-off-by: Omar Sandoval <osandov@osandov.com>
drgn is currently licensed as GPLv3+. Part of the long term vision for
drgn is that other projects can use it as a library providing
programmatic interfaces for debugger functionality. A more permissive
license is better suited to this goal. We decided on LGPLv2.1+ as a good
balance between software freedom and permissiveness.
All contributors not employed by Meta were contacted via email and
consented to the license change. The only exception was the author of
commit c4fbf7e589 ("libdrgn: fix for compilation error"), who did not
respond. That commit reverted a single line of code to one originally
written by me in commit 640b1c011d ("libdrgn: embed DWARF index in
DWARF info cache").
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Rename DW_TAG_{UNKNOWN_FORMAT,BUF_LEN} to
DW_TAG_STR_{UNKNOWN_FORMAT,BUF_LEN} to make it more clear that they're
for dw_tag_str.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Eventually, modules will be exposed as part of the public libdrgn API,
so they should have a clean name. Additionally, the module API I'm
currently working on will allow modules for which we don't have the
debug info file, so "debug info module" would be a misnomer.
Also rename drgn_dwarf_module_info to drgn_module_dwarf_info and
drgn_orc_module_info to drgn_module_orc_info to fit the new naming
scheme better.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
This time, in order to work on both GCC and Clang, use
__attribute__((__fallthrough__)) instead of /* fallthrough */ comments.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Jakub Kicinski reported that
prog.crashed_thread().stack_trace()[1]['does not exist'] segfaulted on a
vmcore he encountered. The segfault was a NULL pointer dereference of
dwarf_diename() of a DW_TAG_subprogram DIE in
drgn_find_in_dwarf_scopes(). The fix is to ignore DIEs without a name.
I was curious what this anonymous DW_TAG_subprogram was. It turned out
to be some dubious DWARF generated by Clang when a local variable is
defined via a macro. One such example comes from the following code in
arch/x86/events/intel/uncore.h:
static inline bool uncore_mmio_is_valid_offset(struct intel_uncore_box *box,
unsigned long offset)
{
if (offset < box->pmu->type->mmio_map_size)
return true;
pr_warn_once("perf uncore: Invalid offset 0x%lx exceeds mapped area of %s.\n",
offset, box->pmu->type->name);
return false;
}
pr_warn_once() expands to:
#define pr_warn_once(fmt, ...) \
printk_once(KERN_WARNING pr_fmt(fmt), ##__VA_ARGS__)
#define printk_once(fmt, ...) \
({ \
static bool __section(".data.once") __print_once; \
bool __ret_print_once = !__print_once; \
\
if (!__print_once) { \
__print_once = true; \
printk(fmt, ##__VA_ARGS__); \
} \
unlikely(__ret_print_once); \
})
For some reason, Clang generates an anonymous, top-level
DW_TAG_subprogram DIE to contain the __print_once variable:
<1><1cf86e>: Abbrev Number: 62 (DW_TAG_subprogram)
<2><1cf86f>: Abbrev Number: 61 (DW_TAG_variable)
<1cf870> DW_AT_name : (indirect string, offset: 0x34fb2e): __print_once
<1cf874> DW_AT_type : <0x1c574c>
<1cf878> DW_AT_decl_file : 1
<1cf879> DW_AT_decl_line : 229
<1cf87a> DW_AT_location : 16 byte block: 3 2c 84 66 83 ff ff ff ff 94 1 31 1e 30 22 9f (DW_OP_addr: ffffffff8366842c; DW_OP_deref_size: 1; DW_OP_lit1; DW_OP_mul; DW_OP_lit0; DW_OP_plus; DW_OP_stack_value)
Whereas GCC puts it in a DW_TAG_lexical block DIE inside of the
DW_TAG_subprogram DIE for uncore_mmio_is_valid_offset():
<1><3110b2>: Abbrev Number: 45 (DW_TAG_subprogram)
<3110b3> DW_AT_name : (indirect string, offset: 0x2e13e): uncore_mmio_is_valid_offset
<3110b7> DW_AT_decl_file : 4
<3110b8> DW_AT_decl_line : 223
<3110b9> DW_AT_decl_column : 20
<3110ba> DW_AT_prototyped : 1
<3110ba> DW_AT_type : <0x2f416b>
<3110be> DW_AT_inline : 3 (declared as inline and inlined)
<3110bf> DW_AT_sibling : <0x311142>
<2><3110ef>: Abbrev Number: 66 (DW_TAG_lexical_block)
<3><3110f0>: Abbrev Number: 120 (DW_TAG_variable)
<3110f1> DW_AT_name : (indirect string, offset: 0x2da3f): __print_once
<3110f5> DW_AT_decl_file : 4
<3110f6> DW_AT_decl_line : 229
<3110f7> DW_AT_decl_column : 2
<3110f8> DW_AT_type : <0x2f416b>
<3110fc> DW_AT_location : 9 byte block: 3 2c 28 48 83 ff ff ff ff (DW_OP_addr: ffffffff8348282c)
Regardless, we shouldn't crash on this input.
Reported-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Omar Sandoval <osandov@osandov.com>
drgn_debug_info_find_complete() looks up the name of the incomplete type
in the global namespace. This is incorrect for C++: we need to look it
up in the namespace that the DIE is in.
To find the containing namespace, we need to do a DIE ancestor walk. We
don't want to do this for C, so add a flag indicating whether a language
has namespaces to struct drgn_language. If it's true, then we do the
ancestor walk and then look up the name in the appropriate namespace.
Signed-off-by: Jay Kamat <jaygkamat@gmail.com>
Previously `drgn` did not recognize the `DW_ATE_UTF` encoding for base
types, and consequently could not handle `char8_t`, `char16_t`, or
`char32_t`. This has been remedied, and a corresponding test case added
to prevent regressions.
Signed-off-by: Kevin Svetlitski <svetlitski@fb.com>
The RA_SIGN_STATE pseudo-register indicates whether the return address
is signed with a pointer authentication code. Add it to the register
definitions. It can be set through a normal CFI register rule or the
vendor-specific DW_CFA_AARCH64_negate_ra_state rule.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
GCC and Clang have 128-bit integer types on 64-bit targets: __int128 and
unsigned __int128. Clang additionally has N-bit integers of up to 2<<24
bits with _ExtInt(N), which was standardized in C23 as _BitInt(N).
Currently, we disallow creating objects with a >64-bit integer type. Jay
Kamat reported that this would cause errors when examining some
binaries. The reason we disallow this is that we don't have a way to
represent or do operations on >64-bit values. We could make use of a
bignum library like GMP to do this in the future.
However, for now, we can loosen this restriction and at least allow
reference and absent objects with big integer types. This requires
enforcing two things: that we never create a value object with a >64-bit
integer type, and that we never read the value of a reference object
with a >64-bit integer type.
Co-authored-by: Jay Kamat <jaygkamat@gmail.com>
Signed-off-by: Omar Sandoval <osandov@osandov.com>
On gcc version 7.3, we get following compilation error
CC libdrgnimpl_la-dwarf_info.lo
../../libdrgn/dwarf_info.c:181:51: error: initializer element is not
constant
static const size_t DRGN_DWARF_INDEX_NUM_SHARDS = 1 <<
DRGN_DWARF_INDEX_SHARD_BITS;
This fixes the compilation error on older versions of gcc
Signed-off-by: Alakesh Haloi <alakesh.haloi@gmail.com>
Issue #130 reported an "unknown attribute form 0x1f20" from drgn. 0x1f20
is DW_FORM_GNU_ref_alt, which is a reference to a DIE in an alternate
file. Similarly, DW_FORM_GNU_strp_alt is a string in an alternate file.
The alternate file is specified by the .gnu_debugaltlink section. This
is generated by dwz, which is used by at least Fedora and Debian.
libdwfl already finds the alternate debug info file, so we can save its
.debug_info and .debug_str and use those to support DW_FORM_GNU_ref_alt
and DW_FORM_GNU_strp_alt in the DWARF index.
Imported units are going to be more work to support in the DWARF index,
but this at least lets drgn start up.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
The upcoming introduction of a higher level data structure to represent
a namespace has implications on the organization of the DWARF index and
debug info management code. Basically, we're going to want to track what
is currently known as struct drgn_dwarf_index_namespace as part of the
new struct drgn_namespace. That only leaves the DWARF specification map
and list of CUs in struct drgn_dwarf_index, which doesn't make much
sense anymore. Instead, let's:
* Move the specification map and CUs into struct drgn_dwarf_info.
* Rename struct drgn_dwarf_index_namespace to struct
drgn_namespace_dwarf_index to indicate that it is the "DWARF index for
a namespace" rather than a "namespace of a DWARF index".
* Move the DWARF index implementation into dwarf_info.c. The DWARF index
and debugging information management have always been coupled, so this
makes it more explicit and is more convenient.
* Improve documentation and naming in the DWARF index implementation.
Now, the only DWARF-specific code outside of dwarf_info.c is for stack
tracing, but we'll leave that for another day.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Continuing the refactoring from the previous commit, move the DWARF code
from debug_info.c to its own file, leaving only the generic ELF file
management in debug_info.c
Signed-off-by: Omar Sandoval <osandov@osandov.com>
