Messages in this thread |  | | Date | Fri, 17 Jul 2009 22:28:25 +0200 | From | Sam Ravnborg <> | Subject | Re: [RFC][ PATCH -tip v2 3/7] Kbuild: disable gcc crossjumping |
| |
On Sat, Jun 27, 2009 at 04:13:04PM -0400, Steven Rostedt wrote: > > A change like this requires an ACK from Sam Ravnborg. > > -- Steve
Overdue review...
I do not know the gcc option so I cannot comment on theeffect of it.
> > > > > diff --git a/Makefile b/Makefile > > index 2903e13..f73b139 100644 > > --- a/Makefile > > +++ b/Makefile > > @@ -524,6 +524,10 @@ else > > KBUILD_CFLAGS += -O2 > > endif > > > > +ifdef CONFIG_DISABLE_CROSSJUMP > > +KBUILD_CFLAGS += -fno-crossjumping > > +endif > > + > > include $(srctree)/arch/$(SRCARCH)/Makefile
Why do we add this option _before_ we include the arch specific Makefile? If we do not want the arch specific Makefile to undo this then move it lower.
Also please add a comment what the effect of the disabling is. There is no reason I should fire up info gcc to find out what -fno-crossjumping is about.
> > > > ifneq ($(CONFIG_FRAME_WARN),0) > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > > index 8da7467..f88e6b8 100644 > > --- a/lib/Kconfig.debug > > +++ b/lib/Kconfig.debug > > @@ -673,6 +673,13 @@ config FRAME_POINTER > > larger and slower, but it gives very useful debugging information > > in case of kernel bugs. (precise oopses/stacktraces/warnings) > > > > +config DISABLE_CROSSJUMP > > + bool "Disable cross-function jump optimization" > > + help > > + This build option disables cross-function jump optimization > > + (crossjumping) of gcc. Disabling crossjumping might increase > > + kernel binary size a little.
So the above comment tells me that is I disable crossjumping I will increase the kernel image a little. That is by no means a good explanation.
Please explain the potential advantage of disabling crossjumping.
Sam
|  |