On Tuesday, 18 November 2014 at 16:49:55 UTC, Marco Leise wrote:
Without fully understanding the issue, omitting the frame
pointer on GNU amd64 systems is the default and is supposed to
work using DWARF debug information. So there should be no need
for a stack frame pointer, right?
Firstly, does DMD generate DWARF debug information in practice
that's correct enough to substitute stack frames? As far as I can
tell, it doesn't.
Second, there's still the argument that not every debugger and
profiler can take advantage of the DWARF debug information. It's
certainly nowhere as easy: from the technical point of view, but
also from a legal one, considering that (IIRC) most libraries
dealing with DWARF debug information are GPL or LGPL, meaning we
can't use them in the D runtime. And indeed, for printing the
stack trace for an unhandled exception, Druntime currently walks
the stack frames:
https://github.com/D-Programming-Language/druntime/blob/master/src/core/runtime.d#L452-L478
There is also the libc backtrace function, which the D runtime
apparently used at some point:
http://www.gnu.org/software/libc/manual/html_node/Backtraces.html
It was removed in this commit:
https://github.com/D-Programming-Language/druntime/commit/9dca50fe65402fb3cdfbb689f1aca58dc835dce4
The commit message doesn't seem to mention why the use of the
backtrace function was removed. But from reading the function's
documentation, it looks like it works in the same way (walking
the stack frame pointers, i.e. also reliant on stack frames).
