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# core.internal.backtrace.dwarf

Generates a human-readable stack-trace on POSIX targets using DWARF
The common use case for printing a stack trace is when toString is called on a Throwable (see object.d). It will iterate on what is likely to be the default trace handler (see core.runtime : defaultTraceHandler). The class returned by defaultTraceHandler is what ends up calling into this module, through the use of core.internal.traits : externDFunc.
The entry point of this module is traceHandlerOpApplyImpl, and the only really "public" symbol (since all rt symbols are private). In the future, this implementation should probably be made idiomatic, so that it can for example work with attributes.

Resilience As this module is used for diagnostic, it should handle failures as gracefully as possible. Having the runtime error out on printing the stack trace one is trying to debug would be quite a terrible UX. For this reason, this module works on a "best effort" basis and will sometimes print mangled symbols, or "???" when it cannot do anything more useful.

Source of data This module uses two main sources for generating human-readable data. First, it uses backtrace_symbols to obtain the name of the symbols (functions or methods) associated with the addresses. Since the names are mangled, it will also call into core.demangle, and doesn't need to use any DWARF information for this, however a future extension could make use of the call frame information (See DWARF4 "6.4 Call Frame Information", PDF page 126).

The other piece of data used is the DWARF .debug_line section, which contains the line informations of a program, necessary to associate the instruction address with its (file, line) information.
Since debug lines informations are quite large, they are encoded using a program that is to be fed to a finite state machine. See runStateMachine and readLineNumberProgram for more details.

DWARF Version This module only supports DWARF 3, 4 and 5.

Reference http://www.dwarfstd.org/

License:
Boost License 1.0.
Authors:
Yazan Dabain, Sean Kelly

Source rt/backtrace/dwarf.d

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