fix(lua): Use lua_tonumber to support 32-bit platforms
#4369
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Previously, `luaC_tovalue` used `lua_tointeger` for variables of type "derive", "counter", and "absolute". However, on 32-bit platforms, `lua_Integer` may be only 32 bits wide [1], so if you set `values` to a value larger than 2^31-1 from Lua, the value of `lua_tointeger` will be unspecified [2]. This commit changes the code to use `lua_tonumber` on 32-bit platforms, which returns a float, which will then be cast to the (typedef'ed to `[u]int64_t`) integer types `derive_t`, `counter_t`, and `absolute_t`, ensuring that large values are not truncated. When `lua_Integer` is 64 bits wide, the code will still use `lua_tointeger` to ensure that integers between 2^53 and 2^63-1 do not lose precision on newer versions of Lua with dedicated integer types [3]. [1]: https://www.lua.org/manual/5.1/manual.html#lua_Integer [2]: https://www.lua.org/manual/5.1/manual.html#lua_tointeger [3]: https://www.lua.org/manual/5.3/manual.html#8.1
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Currently, if you set a value larger than 2^31-1 from Lua on a 32-bit platform, collectd will truncate the value to 0, as this is what `lua_tointeger` returns on Lua 5.1 with a 32-bit `lua_Integer`. This commit modifies the `collectd-mod-lua` plugin to use `lua_tonumber` to first get the value as a float, and then cast it to the appropriate (>32 bit) integer type, ensuring that large values are not truncated. See also: - collectd/collectd#4369 - mstojek/nlbw2collectd#11 Signed-off-by: Max Chernoff <git@maxchernoff.ca>
gucci-on-fleek
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Jun 24, 2025
Currently, if you set a value larger than 2^31-1 from Lua on a 32-bit platform, collectd will truncate the value to 0, as this is what `lua_tointeger` returns on Lua 5.1 with a 32-bit `lua_Integer`. This commit modifies the `collectd-mod-lua` plugin to use `lua_tonumber` to first get the value as a float, and then cast it to the appropriate (>32 bit) integer type, ensuring that large values are not truncated. See also: - collectd/collectd#4369 - mstojek/nlbw2collectd#11 Signed-off-by: Max Chernoff <git@maxchernoff.ca>
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Previously,
luaC_tovalueusedlua_tointegerfor variables of type "derive", "counter", and "absolute". However, on 32-bit platforms,lua_Integermay be only 32 bits wide, so if you setvaluesto a value larger than 2^31-1 from Lua, the value oflua_tointegerwill be unspecified.This commit changes the code to use
lua_tonumberon 32-bit platforms, which returns a float, which will then be cast to the (typedef'ed to[u]int64_t) integer typesderive_t, counter_t, andabsolute_t`, ensuring that large values are not truncated.When
lua_Integeris 64 bits wide, the code will still uselua_tointegerto ensure that integers between 2^53 and 2^63-1 do not lose precision on newer versions of Lua with dedicated integer types.I've only personally tested this patch on a 32-bit platform, but in theory this patch shouldn't affect 64-bit platforms at all.
ChangeLog: Lua plugin: Support "derive", "counter", and "absolute" values >2^31 on 32-bit platforms.