3e40abbc09
Changes: Doing this always in precompiled mode meant increased data segment sizes when CodeSourceMaps are stored, since encoded line/column information is larger in the LEB-like encoding used. Now we only store column information when we produce non-symbolic stacks, since the increased space needed to store the columns is instead in DWARF sections and can be stripped or elided. Original description: Previously, we passed line number information to the stack trace printer and to DWARF by changing the non-special positions in the CodeSourceMap to line numbers in precompiled mode. However, doing this lost column information. We get the column information back in the majority of cases by encoding the line number and column information when neither is too large to pack together into 30 bits. (Here, 20 bits for line and 10 bits for column.) Otherwise, we just store the line information as before, though due to using a bit to encode whether column info exists, it's reduced to 30 bits. If the line info is too big for that, we just return kNoSourcePos. Cq-Include-Trybots: luci.dart.try:vm-kernel-precomp-nnbd-linux-release-x64-try,vm-kernel-precomp-linux-release-x64-try,vm-kernel-precomp-linux-product-x64-try,vm-kernel-precomp-linux-debug-x64-try,vm-kernel-precomp-linux-release-simarm_x64-try Change-Id: Ia8baee71468da6100a170fa305d03059ffd17f78 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/151822 Commit-Queue: Tess Strickland <sstrickl@google.com> Reviewed-by: Martin Kustermann <kustermann@google.com> |
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native_stack_traces
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.
$ pub get native_stack_traces
$ 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.
$ dart2native -k aot -S throws.debug -o throws.aotsnapshot throws.dart
# Run the program, saving the error output to throws.err.
$ dartaotruntime throws.aotsnapshot 2>throws.err
# Using the saved debugging information, we can translate the stack trace
# contained in throws.err to its symbolic form.
$ pub global run native_stack_traces:decode translate -d throws.debug -i throws.err
# We can also just pipe the output of running the program directly into
# the utility.
$ dartaotruntime throws.aotsnapshot |& \
pub global run native_stack_traces:decode translate -d throws.debug
Features and bugs
Please file feature requests and bugs at the issue tracker.