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Fix two UBSan reports: MCU name lookup past the names array, negative left shift in BRBS/BRBC - #594
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… left shift in BRBS/BRBC avr_make_mcu_by_name stops at a NULL alias, but a core that fills all 4 names slots has none, so the loop read past the array. Bound it by the array's size. BRBS/BRBC computed the target as new_pc + (o << 1) with a negative offset, a left shift of a negative value (undefined behaviour); o * 2 is the same without it.
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Building simavr with
-fsanitize=address,undefinedreports two spots:sim_avr.c:runtime error: index 4 out of bounds for type 'const char *[4]'inavr_make_mcu_by_name. The inner loop stops at a NULL alias, but a core that fills all 4namesslots has none, so it reads past the array. The loop is now bounded byARRAY_SIZE(names)as well.sim_core.c:runtime error: left shift of negative value -2in BRBS/BRBC:new_pc + (o << 1)with a negative offset.o * 2gives the same target without the undefined behaviour.No change in behaviour on the compilers I tried; it lets simavr run under the sanitizers cleanly. We carry it as a patch on v1.8 and ran our simavr-driven test suite (ASan + UBSan, simavr instrumented) with it.