On Fri, Feb 8, 2019 at 9:26 AM Thomas Schwinge <tho...@codesourcery.com> wrote: > > 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?
I think that at least for backtrace_full and backtrace_print we are arguably looking at the SKIP parameter in the wrong place. We shouldn't look at it in unwind before calling backtrace_pcinfo. We should count the inlined functions found by backtrace_pcinfo against the SKIP parameter. Ian
