Currently-harmless UB in stack_reset() and stack_reallocate() #2881
Description
Reported here.
clang w/ -fsanitize=undefied reports:
../src/exec_stack.h:64:32: runtime error: applying zero offset to null pointer
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior ../src/exec_stack.h:64:32 in
../src/exec_stack.h:83:36: runtime error: applying zero offset to null pointer
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior ../src/exec_stack.h:83:36 in
These are cases doing pointer arithmetic with NULL pointers and then yield NULL pointers. If the compiler were to try to optimize these functions away due to this, then that would cause jq to break immediately -- the tests certainly wouldn't pass, especially with valgrind. Therefore it is safe to say that for all the tested builds of jq this bit of UB is not currently a problem.