Tess Strickland
a6d06b59ec
Since the virtual addresses in ELF snapshots are the same as in separately saved debugging information, print the virtual address in non-symbolic frames again when running from a snapshot compiled directly to ELF." Storing the relocated address as an extra field in the Image header, which requires increasing the Image header size on 64-bit platforms, means Image pages cannot be used reliably as HeapPages as objects no longer start after kMaxObjectAlignment bytes. Instead, we return to an older design that just uses the lowest bit in the BSS offset to store whether the instructions in an Image were compiled directly to ELF. Cq-Include-Trybots: luci.dart.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-win-release-x64-try,vm-kernel-precomp-linux-release-simarm_x64-try,vm-precomp-ffi-qemu-linux-release-arm-try Change-Id: I3819b0dc2719d69f5e8764ca8be8c6ae7171a7bc Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/146560 Reviewed-by: Ryan Macnak <rmacnak@google.com> Reviewed-by: Vyacheslav Egorov <vegorov@google.com> Commit-Queue: Tess Strickland <sstrickl@google.com>
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.