Tess Strickland
38ef28a058
This is the initial framework for creating snapshots as Mach-O dynamic
libraries. Note that this framework is not 100% feature complete
compared to generating Mach-O snapshots via assembly. In particular,
the directly-compiled Mach-O dylib does not yet contain compact
unwinding information.
Other changes:
* Adds UuidCommand to the native_stack_traces package's Mach-O reader,
which now appropriately returns the UUID as the build ID for Mach-O
shared objects.
* Adds Utils::Basename(path) for portably retrieving the basename
from a path. (Returns nullptr for all arguments where it is not
currently implemented on Fuchsia or Windows.)
* Adjusts vm/timeline.h to avoid pulling in <mach_o/loader.h> on MacOS,
as that interferes with uses of the namespaced Mach-O definitions
in platform/mach_o.h.
* Only attempt to dlopen() a snapshot if ELF is the native format
for the host platform or the snapshot is not an ELF shared object.
If dlopen() is used, report the error message if it fails rather
than attempting to manually load the snapshot as an ELF shared object.
* Fix the magic number stored in DylibAppSnapshot for loaded non-ELF
dynamic libraries.
* Remove the detection of reverse-endian Mach-O magic numbers in
DartUtils::SniffForMagicNumber(), since all our Mach-O related code
assumes host-endian Mach-O files and so there's no point other than
to give a slightly better error message when failing.
TEST=vm/dart/exported_symbols_test
vm/dart/unobfuscated_static_symbols_test
vm/dart/use_dwarf_stack_traces_flag_test
vm/cc/CanDetectMachOFiles
Issue: https://github.com/dart-lang/sdk/issues/60307
Change-Id: Idf5b49d6c6d035ab033509613212b95520d65965
Cq-Include-Trybots: luci.dart.try:vm-aot-linux-debug-x64-try,vm-mac-release-arm64-try,vm-aot-mac-release-arm64-try,vm-aot-mac-release-x64-try,vm-aot-dwarf-linux-product-x64-try,vm-linux-debug-x64-try,vm-mac-debug-arm64-try,vm-fuchsia-release-x64-try,vm-fuchsia-release-arm64-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/415020
Reviewed-by: Slava Egorov <vegorov@google.com>
Commit-Queue: Tess Strickland <sstrickl@google.com>
This package provides libraries and a utility for decoding non-symbolic stack traces generated by an AOT-compiled Dart application.
Converting stack traces
In some modes of AOT compilation, information on mapping execution points to source locations is no longer stored in the Dart image. Instead, this information is translated to separately stored debugging information. This debugging information can then be stripped from the application before shipping.
However, there is a drawback. Stack traces generated by such an application no longer includes file, function, and line number information (i.e., symbolic stack traces). Instead, stack trace frames simply include program counter information. Thus, to find the source information for these frames, we must use the debugging information. This means either keeping the original unstripped application, or saving the debugging information into a separate file.
Given this debugging information, the libraries in this package can turn
non-symbolic stack traces back into symbolic stack traces. In addition, this
package includes a command line tool decode whose output is the same as its
input except that non-symbolic stack traces are translated.
Using decode
Take the following Dart code, which we put in throws.dart. The inlining
pragmas are here just to ensure that bar is inlined into foo and that foo
is not inlined into bar, to illustrate how inlined code is handled in the
translated output.
@pragma('vm:prefer-inline')
bar() => throw Null;
@pragma('vm:never-inline')
foo() => bar();
main() => foo();
Now we run the following commands:
# Make sure that we have the native_stack_traces package.
$ dart pub global activate native_stack_traces
# We compile the example program, removing the source location information
# from the snapshot and saving the debugging information into throws.debug.
$ dart compile exe -S throws.debug throws.dart
# Run the program, saving the error output to throws.err.
$ ./throws.exe 2>throws.err
# Using the saved debugging information, we can translate the stack trace
# contained in throws.err to its symbolic form.
$ dart pub global run native_stack_traces:decode translate -d throws.debug -i throws.err
Features and bugs
Please file feature requests and bugs at the issue tracker.