Created attachment 23298 [details]
testcase.

When compiling the attached test program for i.e. -mcpu=cortex-a9 -marm the tail call mechanism works correctly ... if you replace -marm for -mthumb then the result is a traditional stack frame, for which i couldn't find any switches to turn it off.

For example, this was taken from the example code for -mthumb:


func_c:
        @ args = 0, pretend = 0, frame = 0
        @ frame_needed = 0, uses_anonymous_args = 0
        push    {lr}
        movs    r3, #33
        bl      func_a
        pop     {pc}
        .size   func_c, .-func_c

And this for -marm:


func_c:
        @ args = 0, pretend = 0, frame = 0
        @ frame_needed = 0, uses_anonymous_args = 0
        @ link register save eliminated.
        mov     r3, #33
        b       func_a
        .size   func_c, .-func_c


This is more relevant for example to -mcpu=cortex-m3 where we have no ram to waste.