Re: [XFRM] Make XFRM core subsystem af-independent

["David S. Miller" <davem@xxxxxxxxxxxxx>]

On Sat, 18 Sep 2004 08:50:03 +0900 (JST)
YOSHIFUJI Hideaki / 吉藤英明 <yoshfuji@xxxxxxxxxxxxxx> wrote:

>  2. David's one
>     - maintenancability will be improved
>     - maintains exported symbols for binary-only modules.
>     - more function call and more stack usage.

Compiler is smarter than you think :-)

The whole stack frame is eliminated, because gcc
optimizes it away using tail-call optimizations.

Look at the assembler output for
net/ipv4/route.c:ip_route_output_key() after applying
my changes.

On sparc64 it looks like this:

ip_route_output_key:
        mov     0, %o2
        mov     0, %o3
        or      %o7, %g0, %g1
        call    ip_route_output_flow, 0
         or     %g1, %g0, %o7

No stack frame allocated at all, it basically amounts to
a branch and clearing two argument registers.