2018-07-09 20:39 GMT+09:00 Dirk Gouders <dirk@xxxxxxxxxxx>:
> Dirk Gouders <dirk@xxxxxxxxxxx> writes:
>
>> Dirk Gouders <dirk@xxxxxxxxxxx> writes:
>>
>>> Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> writes:
>>>
>>>> syncconfig updates the .config only when sym_change_count > 0, i.e.
>>>> any change in config symbols has been detected.
>>>>
>>>> Not only symbols but also comments are contained in the .config file.
>>>> If only comments are updated, they are not fed back to the .config,
>>>> then the stale comments are left-over. Of course, this is just a
>>>> matter of comments, but why not fix it.
>>>
>>> Hello Masahiro,
>>>
>>> I am currently looking at and testing this series.
>>>
>>> First: For this patch I would suggest to also edit the syncconfig
>>> section of "conf --help".
>>>
>>> Further, on a slow laptop, I was suspecting, this patch to cause full
>>> rebuilds of everything, each time I ran "make syncconfig" followed by
>>> "make" but could not verify this on another machine, so perhaps I am
>>> just (for testing purposes) removing the wrong files (modules.builtin
>>> for example) -- I am still testing.
>>>
>>> But, what irritates me with testing is that (also without your
>>> patches) two consecutive "make" produce different output, one of them
>>> always shows a warning and this is reproducable. I just want to make
>>> sure there is no other problem that influences my testing:
>>>
>>> $ make
>>> CALL scripts/checksyscalls.sh
>>> DESCEND objtool
>>> CHK include/generated/compile.h
>>> DATAREL arch/x86/boot/compressed/vmlinux
>>> Kernel: arch/x86/boot/bzImage is ready (#15)
>>> Building modules, stage 2.
>>> MODPOST 211 modules
>>>
>>> $ make
>>> CALL scripts/checksyscalls.sh
>>> DESCEND objtool
>>> CHK include/generated/compile.h
>>> LD arch/x86/boot/compressed/vmlinux
>>> ld: arch/x86/boot/compressed/head_64.o: warning: relocation in read-only section `.head.text'
>>> ld: warning: creating a DT_TEXTREL in object.
>>> ZOFFSET arch/x86/boot/zoffset.h
>>> AS arch/x86/boot/header.o
>>> LD arch/x86/boot/setup.elf
>>> OBJCOPY arch/x86/boot/setup.bin
>>> OBJCOPY arch/x86/boot/vmlinux.bin
>>> BUILD arch/x86/boot/bzImage
>>> Setup is 15580 bytes (padded to 15872 bytes).
>>> System is 8069 kB
>>> CRC e01d75ec
>>> Kernel: arch/x86/boot/bzImage is ready (#15)
>>> Building modules, stage 2.
>>> MODPOST 211 modules
>>
>> I spent some more time with the behaviour described above and bisected
>> to the commit after that two consecutive invocations of "make" (on an
>> already compiled tree) seem to do different things. That commit is
>> 98f78525371b55cc (x86/boot: Refuse to build with data relocations), so I
>> put Kees and Ingo on CC.
>>
>> I did the bisecting on another system, so I'll provide the output of two
>> consecutive "make" on an already compiled tree on that machine:
>>
>> $ make
>> CALL scripts/checksyscalls.sh
>> DESCEND objtool
>> CHK include/generated/compile.h
>> DATAREL arch/x86/boot/compressed/vmlinux
>> Kernel: arch/x86/boot/bzImage is ready (#48)
>> Building modules, stage 2.
>> MODPOST 165 modules
>>
>> $ make
>> CALL scripts/checksyscalls.sh
>> DESCEND objtool
>> CHK include/generated/compile.h
>> LD arch/x86/boot/compressed/vmlinux
>> ZOFFSET arch/x86/boot/zoffset.h
>> AS arch/x86/boot/header.o
>> LD arch/x86/boot/setup.elf
>> OBJCOPY arch/x86/boot/setup.bin
>> OBJCOPY arch/x86/boot/vmlinux.bin
>> BUILD arch/x86/boot/bzImage
>> Setup is 15644 bytes (padded to 15872 bytes).
>> System is 6663 kB
>> CRC 3eb90f40
>> Kernel: arch/x86/boot/bzImage is ready (#48)
>> Building modules, stage 2.
>> MODPOST 165 modules
>>
>> If I comment out $(call if_changed,check_data_rel) in
>> arch/x86/boot/compressed/Makefile, two consecutive "make" produce
>> identical output i.e. seem to not do different things:
>>
>> $ make
>> CALL scripts/checksyscalls.sh
>> DESCEND objtool
>> CHK include/generated/compile.h
>> Kernel: arch/x86/boot/bzImage is ready (#49)
>> Building modules, stage 2.
>> MODPOST 165 modules
>>
>> $ make
>> CALL scripts/checksyscalls.sh
>> DESCEND objtool
>> CHK include/generated/compile.h
>> Kernel: arch/x86/boot/bzImage is ready (#49)
>> Building modules, stage 2.
>> MODPOST 165 modules
>>
>> So, I guess this different behaviour of two consecutive "make" is not
>> intentional but I am failing to understand why it happens.
>
> I think, I solved the puzzle and perhaps, that saves others some time:
>
> The problem is that "if_changed" was not designed for multiple use
> inside a recipe and in the case of compressed/vmlinux, the 2-fold use
> created a kind of flip-flop for situations when nothing has to be done
> to build the target.
>
> Because each of the two users of "if_changed" stores it's footprint in
> .vmlinux.cmd but that file then isn't re-read, one of the two
> "if_changed" calculates that nothing has to be done wheras the other one
> recognizes a change in the commandline, because it sees the command-line
> for the other part of the reciepe.
>
> In the next make, the roles flip, because the previously satisfied
> "if_changed" now sees the command-line of the other one. And so on...
>
> I am not a Kbuild expert but the attached patch fixes that problem by
> introducing "if_changed_multi" that accepts two commands -- one whose
> commandline should be checked and a second one that should be
> executed.
if_changed should not appear multiple times in one target.
I think the simplest fix-up is to
create a new command that combines
'cmd_check_data_rel' and 'cmd_ld'.
quiet_cmd_link-vmlinux = LD $@
cmd_link-vmlinux = $(cmd_check_data_rel); $(cmd_ld)
$(obj)/vmlinux: $(vmlinux-objs-y) FORCE
$(call if_changed,link-vmlinux)
Kbuild also supports if_changed_rule,
but the usage is more complex.
There are only a few usages:
https://github.com/torvalds/linux/blob/v4.17/scripts/Makefile.build#L288
> Dirk
>
>
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index fa42f895fdde..f39822fca994 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -107,8 +107,8 @@ define cmd_check_data_rel
> endef
>
> $(obj)/vmlinux: $(vmlinux-objs-y) FORCE
> - $(call if_changed,check_data_rel)
> - $(call if_changed,ld)
> + $(call if_changed_multi,ld,check_data_rel)
> + $(call if_changed_multi,ld,ld)
>
> OBJCOPYFLAGS_vmlinux.bin := -R .comment -S
> $(obj)/vmlinux.bin: vmlinux FORCE
> diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
> index b2d14f1136e8..3bf419319e09 100644
> --- a/scripts/Kbuild.include
> +++ b/scripts/Kbuild.include
> @@ -265,6 +265,23 @@ if_changed = $(if $(strip $(any-prereq) $(arg-check)), \
> $(echo-cmd) $(cmd_$(1)); \
> printf '%s\n' 'cmd_$@ := $(make-cmd)' > $(dot-target).cmd, @:)
>
> +# echo command for command stored in $2
> +# Short version is used, if $(quiet) equals `quiet_', otherwise full one.
> +echo-cmd2 = $(if $($(quiet)cmd_$(2)),\
> + echo ' $(call escsq,$($(quiet)cmd_$(2)))$(echo-why)';)
> +
> +# Execute command arg2 if commandline for command arg1 or prerequisite(s) are
> +# updated.
> +#
> +# This is safe for multiple use inside a recipe; arg1 and arg2 may be
> +# identical.
> +if_changed_multi = $(if $(strip $(any-prereq) $(arg-check)), \
> + @set -e; \
> + $(echo-cmd2) : ; \
> + $(cmd_$(2)); \
> + printf '%s\n' 'cmd_$@ := $(make-cmd)' > $(dot-target).cmd, @:)
> +
> +
> # Execute the command and also postprocess generated .d dependencies file.
> if_changed_dep = $(if $(strip $(any-prereq) $(arg-check) ), \
> @set -e; \
>
--
Best Regards
Masahiro Yamada
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