On 09-02-19 22:07, Ian Lance Taylor wrote: > 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.
FTR, filed as PR89273 - "Count inlined functions in skip parm for backtrace_full and backtrace_print" ( https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89273 ). Thanks, - Tom
