UBSanitizer runtime error: left shift of negative value -1 #5395

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1. marlowa commented on Apr 22, 2026

   

   Andrew Peter Marlow (marlowa)

   on Apr 22, 2026

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   which sanitizer is this you are using? Address? Or thread?
   I am trying to use the thread sanitizer on a C++ program that uses librdkafka and it gets a SEGV as soon as the kafka background threads start. It blows up in a call get getaddrinfo when it tries to get the broker IP addresses from their names via DNS lookup.
2. Ignition commented on Apr 22, 2026

   

   Gareth Andrew Lloyd (Ignition)

   on Apr 22, 2026

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   Andrew Peter Marlow (@marlowa) this was with undefined behaviour sanitizer.
   -fsanitize=undefined

   ATM there are 3 different areas that we currently have to suppress when building with sanitizers.

   # librdkafka: left shift of negative value in zig-zag varint encoder (rdvarint.h:71)
   src:*/rdvarint.h
   
   # librdkafka: signed integer overflow in timestamp conversion (rdkafka_int.h:1171)
   src:*/rdkafka_int.h
   
   # librdkafka: negative shift exponent in HDR histogram (rdhdrhistogram.c:212)
   src:*/rdhdrhistogram.c
   
3. Ivan Milinović (imilinovic)

   added 4 commits that reference this issue on May 10, 2026

   Fix four UBSan-reported undefined behavior sites

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   cf99dfd

   rdvarint: avoid signed left shift UB in zig-zag varint encoder

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   6aec6ea

   rdvarint: avoid signed left shift UB in zig-zag varint encoder

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   2dc7d3e

   rdvarint: avoid signed left shift UB in zig-zag varint encoder

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   3327461