Libx snapshot note (2026-10-02, Asia/Tokyo): This page preserves the official bugs list acquired at 2026-10-01T17:29:12.280720Z. For later reports, see the current official bugs list. The 2026-08-11 snapshot is retained separately.

Lua 5.5.1 1

1. ‘luaO_applyparam’ can be called with a negative parameter, causing a negative value to be left-shifted (undefined behavior). reported by Sergey Bronnikov on 26 Aug 2026. existed since 5.0. fixed in github.

   Example:

   Copy code

   -- To be run with Lua compiled with -fsanitize=undefined
   
   local lim = 1e6
   
   -- make major collections non-incremental
   collectgarbage("param", "stepmul", 0)
   
   -- make "majorminor" large enough to force a left-shift
   -- when applying the parameter (internal details)
   collectgarbage("param", "majorminor", 2000)
   
   collectgarbage(); collectgarbage()
   
   local M = collectgarbage"count"
   
   -- create a large table
   local t = {}
   for i = 1, lim do t[i] = true end
   assert(collectgarbage"count" > M + (lim * string.packsize"j")/1024)
   
   -- force collector to "generational major" mode
   collectgarbage"step"
   collectgarbage"step"
   collectgarbage"step"
   assert(not T or T.gcquery() == "genmajor")
   
   -- shrink the table
   for i = 1, lim do t[i] = nil end
   t[2 * lim] = true
   assert(collectgarbage"count" < M * 5/4)
   
   collectgarbage"step"   -- assert violation

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