I proposed to build Phobos and Druntime with stack frames enabled:
https://issues.dlang.org/show_bug.cgi?id=13726
Stack frames add three CPU instructions to each function (two in
the prolog, and one in the epilog). This creates a linked list
which debuggers, profilers, etc. can easily walk to find which
function called which. They would allow debugging certain classes
of bugs much more easily (e.g. the recurring
InvalidMemoryOperationError - there's a thread about it in
D.learn just today), and profiling your code with polling
(non-instrumenting) profilers.
As I understood, in theory, debug information (DWARF and PDB,
probably not CV) should also contain information allowing an
accurate stack walk, but it doesn't look like we're currently
emitting debug information to that level of accuracy. Not all
debuggers/profilers understand this debug information, either
(whereas walking the linked list emitted by the stack frames is
trivial).
We could also start bundling debug builds of Phobos. However,
these will not help in cases where the performance impact of
using a full-blown debug build is not acceptable (e.g. if it'll
skew the profiling results too much, or if you just want readable
stack frames for your D web service in production).
How much will this cost in performance?
I've run two benchmarks, both show a figure around 0.1%. Many
performance-sensitive parts of Phobos (std.algorithm) are
templated and thus are not affected by the Makefile switches. The
GC is built with -inline, which, although it causes the call
stack to not contain inlined functions, doesn't cause it to
abruptly break off like without stack frames.
Is D the first to build its release stdlib with stack frames?
Nope. Microsoft's C release runtime is built stack frames enabled.
Personally, I think the 0.1% is practically negligible
considering the advantages. My proposal was rejected, so I'd like
to hear more opinions about this. What do you think?
If you want to run some benchmarks yourself, here are the patches:
https://github.com/CyberShadow/phobos/compare/enable-stack-frames?expand=1
https://github.com/CyberShadow/druntime/compare/enable-stack-frames?expand=1
Or, using Digger:
digger build
v2.065.0+CyberShadow/phobos/enable-stack-frames+CyberShadow/druntime/enable-stack-frames
Previous discussion from 2012:
http://forum.dlang.org/post/zebqmrhcigfuockcp...@forum.dlang.org
