Hi,
On Wed, 2009-10-21 at 13:23 -0400, Steven Rostedt wrote:
On Wed, 2009-10-21 at 10:07 -0700, David Daney wrote:
I have not used -pg, so I don't know for sure, I think all it does is
add the calls to _mcount. Someone could investigate
-fno-omit-frame-pointer, with that you may be able to use:
Note, -pg assumes -fno-omit-frame-pointer, since -fomit-frame-pointer
and -pg are incompatible.
Ralf have told me -pg really works with -fomit-frame-pointer, although
the gcc tool tell us they are not incompatible when we use both of them
together, but when I remove -fno-omit-frame-pointer in
KBUILD_FLAGS(enabled by CONFIG_FRAME_POINTER), it definitely remove the
s8(fp) relative source code(Seems -fomit-frame-pionter is used by
default by gcc), the leaf function becomes this:
function:
80101144 <au1k_wait>:
80101144: 03e00821 move at,ra
80101148: 0c04271c jal 80109c70 <_mcount>
No more instruction,
and the non-leaf function becomes,
80126590 <copy_process>:
80126590: 27bdffa0 addiu sp,sp,-96
80126594: afbf005c sw ra,92(sp)
80126598: afbe0058 sw s8,88(sp)
8012659c: afb70054 sw s7,84(sp)
801265a0: afb60050 sw s6,80(sp)
801265a4: afb5004c sw s5,76(sp)
801265a8: afb40048 sw s4,72(sp)
801265ac: afb30044 sw s3,68(sp)
801265b0: afb20040 sw s2,64(sp)
801265b4: afb1003c sw s1,60(sp)
801265b8: afb00038 sw s0,56(sp)
801265bc: 03e00821 move at,ra
801265c0: 0c04271c jal 80109c70 <_mcount>
It may save about two instructions for us.
sw s8, offset(sp)
move s8, fp
and also, I have tried to just search "Save" instruction, if I find one,
that should be a non-leaf function, otherwise, it's leaf function, but I
can not prove no "Save" instruction before the leaf function's "move at,
ra", for example:
8010113c: 03e00008 jr ra
80101140: 00020021 nop
80101144 <au1k_wait>:
80101144: 03e00821 move at,ra
80101148: 0c04271c jal 80109c70 <_mcount>
if there is "save" instruction at address 80101140, it will fail.
Although, I met not failure with several tries, but no prove on it! any
ABI protection for this? if YES, this should be a better solution, for
it may works without -fno-omit-frame-pointer and save several
instructions for us.
