[Bug target/77933] New: Stack corruption on ARM when using high registers and __builtin_return_address

["thopre01 at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77933

            Bug ID: 77933
           Summary: Stack corruption on ARM when using high registers and
                    __builtin_return_address
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: thopre01 at gcc dot gnu.org
  Target Milestone: ---
            Target: arm-none-eabi

When compiling the following testcase with -march=armv6-m -mthumb -O1:

void* foo() {

  asm volatile("" : : : "r8", "r9");

  return __builtin_return_address(0);

}

GCC produces the following assembler:

        mov     r3, r9
        push    {r3, lr}
        mov     r3, r8
        push    {r3, lr}
        mov     r0, lr
        pop     {r2, r3}
        mov     r8, r2
        mov     r9, r3
        pop     {pc}

Note how 4 words are pushed on the stack but only 3 are popped, hence the stack
gets corrupted