http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55757
Timmy Brolin <web at brolinembedded dot se> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |web at brolinembedded dot | |se --- Comment #7 from Timmy Brolin <web at brolinembedded dot se> 2013-03-02 15:23:11 UTC --- (In reply to comment #2) > If you really know that you don't need stack-alignment on an M3, then just > remove the interrupt attribute. It really doesn't serve any other purpose on > M-profile cores other than to cause the stack realignment. What you suggest requires a change in the C-code depending on the processor. That is, one piece of C-code will not compile optimally for different Cortex-M3 revisions without modifications to the C-code itself. This is not good for code which is intended to be used on multiple platforms. Cortex-M3 r0p0 needs the prologue/epilogue. Cortex-M3 r1p0 has a new configuration bit called STKALIGN which when enabled makes the prologue/epilogue unnecessary. (But the default setting is that it still needs the prologue/epilogue) Cortex-M3 r2p0 changed the default setting of STKALIGN so that the prologue/epilogue are unnecessary by default. I would suggest that the prologue/epilogue should be removed by default when compiling for r2p0 or higher, but be kept by default for older revisions. There should also be a compilation switch to manually enable/disable the prologue/epilogue according to the chosen setting of STKALIGN. Interrupts can often be time critical, so ISR entry is probably the worst possible place for extra instructions.