Relinking zImage when nothing changes

[Arnaud Lacombe]

Hi,

On Fri, Aug 12, 2011 at 2:02 PM, Sam Ravnborg <sam at ravnborg.org> wrote:
> On Fri, Aug 12, 2011 at 10:46:24AM -0700, Stephen Boyd wrote:
>> I was hoping with the recent patch e78e8f2 (kernel: prevent unnecessary
>> rebuilding due to config_data.gz, 2011-07-05) compiling ARM linux a
>> second time would amount to no more linking. This doesn't seem to be the
>> case though. Doing a make V=2 I see that lib1funcs.S is shipped and thus
>> we have to recompile it although nothing actually changed. This in turn
>> requires us to relink the compressed vmlinux and then recreate the zImage.
>>
>>   Kernel: arch/arm/boot/Image is ready
>>   SHIPPED arch/arm/boot/compressed/lib1funcs.S - due to missing .cmd file
>>   AS      arch/arm/boot/compressed/lib1funcs.o - due to: arch/arm/boot/compressed/lib1funcs.S
>>   LD      arch/arm/boot/compressed/vmlinux - due to: arch/arm/boot/compressed/lib1funcs.o
>>   OBJCOPY arch/arm/boot/zImage - due to: arch/arm/boot/compressed/vmlinux
>>   Kernel: arch/arm/boot/zImage is ready
>>
>>
>> Is there any way to avoid this? Perhaps the shipped command could become
>> a bit wiser?
>
> Following patch will likely fix it:
> diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
> index 0c74a6f..80b6b6e 100644
> --- a/arch/arm/boot/compressed/Makefile
> +++ b/arch/arm/boot/compressed/Makefile
> @@ -123,7 +123,7 @@ LDFLAGS_vmlinux += -T
>  # For __aeabi_uidivmod
>  lib1funcs = $(obj)/lib1funcs.o
>
> -$(obj)/lib1funcs.S: $(srctree)/arch/$(SRCARCH)/lib/lib1funcs.S FORCE
> +$(obj)/lib1funcs.S: $(srctree)/arch/$(SRCARCH)/lib/lib1funcs.S
>        $(call cmd,shipped)
>
AFAIK, we have a generic rule to handle shipped files:

from scripts/Makefile.lib:

$(obj)/%: $(src)/%_shipped
        $(call cmd,shipped)

so, that rule should not be needed at all.

 - Arnaud

>  # We need to prevent any GOTOFF relocs being used with references
>
> (cut'n'pasted ...)
>
> The FORCE prerequisite will tell make to always execute the command.
> But we only want to execute the command if:
> 1) $(obj)/lib1funcs.S is missing
> 2) or $(srctree)/arch/$(SRCARCH)/lib/lib1funcs.S is not older then $(obj)/lib1funcs.S
>
> So dropping FORCE should be a safe thing to do.
>
>        Sam
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