Messages in this thread |  | | Date | Fri, 17 Jul 2009 17:13:22 -0400 | From | Masami Hiramatsu <> | Subject | Re: [RFC][ PATCH -tip v2 3/7] Kbuild: disable gcc crossjumping |
| |
Sam Ravnborg wrote: > 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.
Thanks for comment. however, as far as I can see, I couldn't find in the difference between binary with -fno-crossjump and without it. So I decided to drop this patch...
> >>> 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.
Sure, I'll write a comment on, next time.
> > >>> >>> 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.
Agreed.
Thank you, -- Masami Hiramatsu
Software Engineer Hitachi Computer Products (America), Inc. Software Solutions Division
e-mail: mhiramat@redhat.com
|  |