One question: Does the omission of sign extension by avr-gcc remain without optimisation for size?
Thank you for your suggestion, I did not think of that. When I compile without any optimization at all, the sign extension by the called function is also missing, like with optimizations enabled. A user on avrfreaks suggested that the paragraph in the AVR-Libc FAQ that causes the confusion might simply be mixing up "called function" and "calling function". is: Return values: 8-bit in r24 (not r25!), ... 8-bit return values are zero/sign-extended to 16 bits by the *called* function (which is actually contradicting itself, as mentioned by another user) should be: Return values: 8-bit in r24 (not r25!), ... 8-bit return values are zero/sign-extended to 16 bits by the *calling* function Also, the avr-gcc ABI page states that 8-bit values are returned in r24 and does not say anything about 8-bit return values being extended to 16 bits by the called function. [1] So I think that the "called" vs "calling" mixup might actually be the answer to my question. Benoit [1] https://gcc.gnu.org/wiki/avr-gcc#Calling_Convention _______________________________________________ AVR-GCC-list mailing list AVR-GCC-list@nongnu.org https://lists.nongnu.org/mailman/listinfo/avr-gcc-list
