[Bug inline-asm/93021] New: SP Clobber change prevents compilation of some bootloaders and operating systems

[rongithub at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93021

            Bug ID: 93021
           Summary: SP Clobber change prevents compilation of some
                    bootloaders and operating systems
           Product: gcc
           Version: 9.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: inline-asm
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rongithub at gmail dot com
  Target Milestone: ---

GCC version 9.3.1 throws an error when inline asm code changes the stack
pointer (see Bug IDs 11807 & 52813).

This change causes GCC to fail when compiling boot loaders that set the SP
before passing control to applications. For instance, the current Adafruit
Metro M4 Express boot loader (https://github.com/adafruit/uf2-samdx1) will not
compile using GCC v 9.3.1, but it builds with v 7.3.1

Perhaps adding a flag that allows the user to explicitly override this feature
when compiling any application in which context changes occur that legitimately
change the SP (e.g., boot loader, OS task switching) would address both issues.