On 08-02-19 18:25, Thomas Schwinge wrote: > Hi Tom! > > On Fri, 8 Feb 2019 10:41:47 +0100, Tom de Vries <tdevr...@suse.de> wrote: >> The backtrace functions backtrace_full, backtrace_print and backtrace_simple >> walk the call stack, but make sure to skip the first entry, in order to skip >> over the functions themselves, and start the backtrace at the caller of the >> functions. >> >> When compiling with -flto, the functions may be inlined, causing them to skip >> over the caller instead. > > So, when recently working on the OpenACC Profiling Interface > implementation in libgomp, where I'm using libbacktrace to figure out the > caller of certain libgomp functions, I recently wondered about the very > same issue, that we reliably have to skip a few initial frames. > > So, "noinline" is how to do that reliably... ;-/ That might be > non-obvious for the casual reader, so they might not understand... > >> Fix this by declaring the functions with __attribute__((noinline)). > > ... this alone. > > I'd suggest to have a common "#define LIBBACKTRACE_NOINLINE [...]" (or > similar), together with the explanatory comment given above, and use that > at the respective definition (or declaration?) sites. Can that go into > the public libbacktrace "*.h" file, so that it can also be used > elsewhere, as described above? > > If you agree, want me to prepare a patch?
Hi Thomas, I suppose adding an explanatory comment at the places where I added "__attribute__((noinline))" could be an improvement. But to me, this is just an implementation detail of the library, and I would avoid changing the public header file. Thanks, - Tom
