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sd-bus: bus_message_type_from_string is not pure
GCC document [1] says: The pure attribute prohibits a function from modifying the state of the program that is observable by means other than inspecting the function’s return value. And there is an example: `int hash (char *) __attribute__ ((pure));` ... Even though hash takes a non-const pointer argument it must not modify the array it points to, ... But we are modifying the object pointed to by the pointer u, which is clearly a violation of the semantic of pure. With -ftrivial-auto-var-init (enabled by -Dmode=release), on some targets (GCC 12.2 on AArch64 and GCC 13.1 on x86_64) performs an optimization: as the variable "u" in bus_match_parse has been zero-initialized (by the -ftrivial-auto-var-init option) and never modified (because a "pure" bus_message_type_from_string is not allowed to modify it), "u" will be always 0. Then 0 is used to initialize .value_u8 field of struct bus_match_component. This then causes a infinite event loop, so "systemctl restart" never stops, and pam_systemd timeouts communicating with logind, etc. So we should remove the "pure" attribute here. Fixes #26395. [1]:https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-pure-function-attribute
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