In my experience, the Arm ecosystem has an excellent track record regarding compatibility across conforming implementations of the architectures (e.g., Armv7-A, ARMv8-A). I can draw a practical comparison to MIPS, where I had to deal with a lot of variability based on various vendor extensions. This is reflected in the "-march=" documentation for GCC:

MIPS: https://gcc.gnu.org/onlinedocs/gcc/MIPS-Options.html AArch64: https://gcc.gnu.org/onlinedocs/gcc/AArch64-Options.html Arm: https://gcc.gnu.org/onlinedocs/gcc/ARM-Options.html