source: src/libcfa/concurrency/CtxSwitch-armv7l.S @ 85b1deb

        @ 32 bit ARM context switch
        @ This function assumes that r9 has no special meaning on the platform it's
        @ being built on.
        @ If r9 is special, uncomment the following line and it will be left alone

        @ #define R9_SPECIAL

        #define PTR_BYTE        4
        #define SP_OFFSET       ( 0 * PTR_BYTE )
        #define FP_OFFSET       ( 1 * PTR_BYTE )
        #define PC_OFFSET       ( 2 * PTR_BYTE )

        .text
        .align  2
        .global CtxSwitch
        .type   CtxSwitch, %function

CtxSwitch:
        @ save callee-saved registers: r4-r8, r10, r11, r13(sp) (plus r9 depending on platform specification)
        @ I've seen reference to 31 registers on 64-bit, if this is the case, more need to be saved
        @ save thread state registers: r14(lr)
        @ r12(ip) is intra-procedure-call scratch register, does not need saving between function calls

        #ifdef R9_SPECIAL
        stmfd r13!, {r4-r8,r10,r11,r14}
        #else
        stmfd r13!, {r4-r11,r14}
        #endif // R9_SPECIAL

        @ save floating point registers: s16-s31
        vstmdb r13!, {s16-s31}

        @ save frame pointer and stack pointer to outgoing datastructure
        str sp, [r0, #SP_OFFSET]
        str fp, [r0, #FP_OFFSET]

        @ restore frame pointer and stack pointer from incoming datastructure
        ldr fp, [r1, #FP_OFFSET]
        ldr sp, [r1, #SP_OFFSET]

        @ restore floating point registers: s16-s31
        vldm r13!, {s16-s31}
        @ restore r14(lr)
        @ restore 64-bit extra registers?
        @ restore callee-saved registers: r4-r8, r10, r11, r13

        #ifdef R9_SPECIAL
        ldmfd r13!, {r4-r8,r10,r11,r15}
        #else
        ldmfd r13!, {r4-r11,r14}    @ loading r14 back into r15 returns

        mov r15, r14
        #endif // R9_SPECIAL
        
        .text
        .align  2
        .global CtxInvokeStub
        .type   CtxInvokeStub, %function

CtxInvokeStub:
        ldmfd r13!, {r0-r1}
        mov r15, r1