The arm ABI defines that the value in register r0 is used as the return
value of a function. To indicate success for get/set/swapcontext (return
value of 0) the register r0 must contain zero at the end of the function
call. Thus set r0 to zero and store it in the context. This context
is restored later and indicate successful execution, because r0 is 0.
The order registers are stored has changed so that only one additional
instruction (mov r0, #0) needs to be added to fix the return value
bug for get/set/swapcontext.
Signed-off-by: Volker Christian <me@vchrist.at>
This is needed because in libucontext.h we include "libucontext/bits.h".
We therefore need to have bits.h in somepath/libucontext/bits.h. In the
Makefile, somepath/freestanding/bits.h was copied to the right path but
in the meson build system, the include copy happens at the end.
Volker Christian
Ariadne Conill