On 26.05.15 15:55, Britton Kerin wrote: > What I don't know is what I must do to ensure that avr-libc isn't using the > registers in an unsafe way. It does use the registers: > > $ avr-objdump -d /usr/lib/avr/lib/libc.a > /tmp/libc > $ egrep '\<r2\>' /tmp/libc | more > 1ac: 28 2e mov r2, r24 > 1f4: 20 2e mov r2, r16 > 204: 82 2d mov r24, r2 > ... > > and apparently since there are no push-pop pairs, it doesn't seem guaranteed > that its saving/restoring them. But I'm told that it might not need to, > because a compiler optimization causes only clobbered registers to be > preserved. I'm told that what I need to check is whether avr-gcc "pushes > the clobber list"?
What do you see when you "avr-objdump -d" the compiled object of a small program which calls one avr-libc function? Does the compiler provide push-pop pairs for registers used both by the calling function and the avr-libc function? It would be less efficient to push everything, whether needed or not. Avr-gcc only needs to protect registers which are in use. What do you find when you look? My recollection of the AVR ABI is that r2-r17 are preserved across function calls. As avr-libc lacks obvious signs of doing that intrinsically, you can either hope that avr-gcc does it, or quickly and easily verify the behaviour by observation. Erik _______________________________________________ AVR-GCC-list mailing list AVR-GCC-list@nongnu.org https://lists.nongnu.org/mailman/listinfo/avr-gcc-list
