| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Lukas Fittl <lukas(at)fittl(dot)com> |
| Cc: | Haibo Yan <tristan(dot)yim(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, David Geier <geidav(dot)pg(at)gmail(dot)com> |
| Subject: | Re: Reduce timing overhead of EXPLAIN ANALYZE using rdtsc? |
| Date: | 2026-04-12 18:20:31 |
| Message-ID: | 343362.1776018031@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Lukas Fittl <lukas(at)fittl(dot)com> writes:
> FWIW, for archive's sake, drongo is green again now, thanks to commit
> 7fc36c5db550 (Avoid CPUID 0x15/0x16 for Hypervisor TSC frequency).
drongo may be happy, but Coverity is not:
166 uint64 loop_count;
167
168 loop_count = test_timing(test_duration, TIMING_CLOCK_SOURCE_SYSTEM, false);
>>> CID 1691465: Incorrect expression (DIVIDE_BY_ZERO)
>>> In function call "output", division by expression "loop_count" which may be zero has undefined behavior.
169 output(loop_count);
AFAICS it's correct to complain. test_timing() visibly can return zero,
but of the three places where test_timing() is followed by output()
only one has a defense against that.
regards, tom lane
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