Tess Strickland
bc021bbc01
In order to appropriately generate .dSYMs for a snapshot and allow
the strip tool to be used on the snapshot afterwards, add a mode that
not only outputs the snapshot (sans DWARF information) but also
an associated relocatable object file that contains the program's DWARF
information. That allows dsymutil to retrieve the DWARF information
from the relocatable object when run on the snapshot prior to stripping.
To specify that the relocatable object file should be output, use
the new --macho-object command line argument to gen_snapshot
to specify where the object file should be written.
This CL also adds an additional command line argument,
--macho-reduce-padding, which reduces the alignment used for segments
and the text/const sections in Mach-O outputs from 16KB to 64 bytes.
The larger padding is needed for some uses, like non-native loading
of Mach-O objects, but can be elided for other uses like Flutter builds.
TEST=vm/dart/use_dwarf_stack_traces_flag_test
vm/dart/use_macho_reduce_padding_flag_test
Change-Id: I2bf4bacb70c41299b8b6fdb7635c2374acf7a07d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/457420
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.