| Message ID | 20160812065011.GB3296@wotan.suse.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, Aug 12, 2016 at 08:50:11AM +0200, Luis R. Rodriguez wrote: > On Fri, Aug 12, 2016 at 07:23:03AM +0200, Borislav Petkov wrote: > > On Fri, Aug 12, 2016 at 05:51:29AM +0200, Luis R. Rodriguez wrote: > > > OK I've added CONFIG_BUILD_AVOID_BITROT. > > > > What does that do? > > > Enabling it allows the forced compilation chosen by maintainers. > Otherwise forced compilations with the new special targets are > ignored. Nice. > I've gone with table-obj-y and table-lib-y as we have > to support both lib-y and obj-y respective targets. > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > index 33e2966dd741..7893e3b8da82 100644 > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -1895,6 +1895,30 @@ config PROVIDE_OHCI1394_DMA_INIT > > See Documentation/debugging-via-ohci1394.txt for more information. > > +config BUILD_AVOID_BITROT > + bool "Always force building specially annotated" ...annotated targets" > + default y > + help > + If enabled then the the special table-* Makefile targets will always > + be forced to be compiled even if their respective CONFIG_ option has > + been disabled, but its objects will only be linked in if the same > + respective CONFIG_ option has been enabled. This helps avoid code > + bit rot issues, use for these targets should be carefully considred > + by maintainers. You can safely enable this option at the expense of > + increasing compile time slightly. Enabling this option helps avoid s/slightly// :-) > + code bit rot by taking advantage of the facilities provided and > + enabled by using linker tables documented under: > + > + include/linux/tables.h > + > + The special targets supported are: > + > + o table-obj-y > + o table-lib-y > + > + Say Y unless you are a grumpy maintainer and don't trust other > + maintainer's judgements on what code should always get compiled. ... or you're running a tiny-config setup ... or you're an embedded, resource-constrained person ... or you simply don't want to have stuff which is forcibly enabled on you even if you're never going to need it ... I got a million o'those :-) Thanks.
On Fri, Aug 12, 2016 at 09:25:07AM +0200, Borislav Petkov wrote: > On Fri, Aug 12, 2016 at 08:50:11AM +0200, Luis R. Rodriguez wrote: > > On Fri, Aug 12, 2016 at 07:23:03AM +0200, Borislav Petkov wrote: > > > On Fri, Aug 12, 2016 at 05:51:29AM +0200, Luis R. Rodriguez wrote: > > > > OK I've added CONFIG_BUILD_AVOID_BITROT. > > > > > > What does that do? > > > > > > Enabling it allows the forced compilation chosen by maintainers. > > Otherwise forced compilations with the new special targets are > > ignored. > > Nice. > > > I've gone with table-obj-y and table-lib-y as we have > > to support both lib-y and obj-y respective targets. > > > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > > index 33e2966dd741..7893e3b8da82 100644 > > --- a/lib/Kconfig.debug > > +++ b/lib/Kconfig.debug > > @@ -1895,6 +1895,30 @@ config PROVIDE_OHCI1394_DMA_INIT > > > > See Documentation/debugging-via-ohci1394.txt for more information. > > > > +config BUILD_AVOID_BITROT > > + bool "Always force building specially annotated" > > ...annotated targets" > > > + default y > > + help > > + If enabled then the the special table-* Makefile targets will always > > + be forced to be compiled even if their respective CONFIG_ option has > > + been disabled, but its objects will only be linked in if the same > > + respective CONFIG_ option has been enabled. This helps avoid code > > + bit rot issues, use for these targets should be carefully considred > > + by maintainers. You can safely enable this option at the expense of > > + increasing compile time slightly. Enabling this option helps avoid > > s/slightly// > > :-) > > > + code bit rot by taking advantage of the facilities provided and > > + enabled by using linker tables documented under: > > + > > + include/linux/tables.h > > + > > + The special targets supported are: > > + > > + o table-obj-y > > + o table-lib-y > > + > > + Say Y unless you are a grumpy maintainer and don't trust other > > + maintainer's judgements on what code should always get compiled. > > ... or you're running a tiny-config setup Even so, you don't link the compiled extra code so the only penalty here is when compiling, nothing more. And if you are compiling typically the cost here is just a few seconds. > ... or you're an embedded, resource-constrained person For the compilation of th kernel ? > ... or you simply don't want to have stuff which is forcibly enabled on you even > if you're never going to need it > ... Which seems to be the same as the reason I noted ? > I got a million o'those :-) I can remove the grumpy maintainer description :) Luis
On Fri, Aug 12, 2016 at 05:28:05PM +0200, Luis R. Rodriguez wrote: > Even so, you don't link the compiled extra code so the only penalty > here is when compiling, nothing more. And if you are compiling typically > the cost here is just a few seconds. Yeah, so let's make it clear that this is similar to COMPILE_TEST and people with fast machines and who don't mind building a couple more seconds longer, should enable it. You don't want to be doing bit-rotting tests on small, weak machines, which barely get done with the build as it is. I have a 32-bit atom which takes hours to build a kernel. Enabling that there is not making the kernel build any more fun. > > ... or you simply don't want to have stuff which is forcibly enabled on you even > > if you're never going to need it > > ... > > Which seems to be the same as the reason I noted ? No, the reason is we don't force stuff down people's throats just because we think we know better. Other people do that. Instead, we help them make an informed decision by describing the feature as precisely as possible. > I can remove the grumpy maintainer description :) Yap :-)
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 33e2966dd741..7893e3b8da82 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -1895,6 +1895,30 @@ config PROVIDE_OHCI1394_DMA_INIT See Documentation/debugging-via-ohci1394.txt for more information. +config BUILD_AVOID_BITROT + bool "Always force building specially annotated" + default y + help + If enabled then the the special table-* Makefile targets will always + be forced to be compiled even if their respective CONFIG_ option has + been disabled, but its objects will only be linked in if the same + respective CONFIG_ option has been enabled. This helps avoid code + bit rot issues, use for these targets should be carefully considred + by maintainers. You can safely enable this option at the expense of + increasing compile time slightly. Enabling this option helps avoid + code bit rot by taking advantage of the facilities provided and + enabled by using linker tables documented under: + + include/linux/tables.h + + The special targets supported are: + + o table-obj-y + o table-lib-y + + Say Y unless you are a grumpy maintainer and don't trust other + maintainer's judgements on what code should always get compiled. + config BUILD_DOCSRC bool "Build targets in Documentation/ tree" depends on HEADERS_CHECK diff --git a/scripts/Makefile.build b/scripts/Makefile.build index 002857fe8d0d..17ced5ac44b2 100644 --- a/scripts/Makefile.build +++ b/scripts/Makefile.build @@ -91,7 +91,8 @@ modorder-target := $(obj)/modules.order # We keep a list of all modules in $(MODVERDIR) -__build: $(if $(KBUILD_BUILTIN),$(builtin-target) $(lib-target) $(extra-y) $(table-y)) \ +__build: $(if $(KBUILD_BUILTIN),$(builtin-target) $(lib-target) $(extra-y) \ + $(table-obj-y)) \ $(if $(KBUILD_MODULES),$(obj-m) $(modorder-target)) \ $(subdir-ym) $(always) @: @@ -325,8 +326,8 @@ cmd_as_o_S = $(CC) $(a_flags) -c -o $@ $< $(obj)/%.o: $(src)/%.S $(objtool_obj) FORCE $(call if_changed_rule,as_o_S) -targets += $(real-objs-y) $(real-objs-m) $(lib-y) -targets += $(extra-y) $(table-y) $(MAKECMDGOALS) $(always) +targets += $(real-objs-y) $(real-objs-m) $(lib-y) $(table-lib-y) +targets += $(extra-y) $(table-obj-y) $(MAKECMDGOALS) $(always) # Linker scripts preprocessor (.lds.S -> .lds) # --------------------------------------------------------------------------- diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib index 494f215ebaa4..58db6b503aca 100644 --- a/scripts/Makefile.lib +++ b/scripts/Makefile.lib @@ -12,15 +12,14 @@ export KBUILD_SUBDIR_CCFLAGS := $(KBUILD_SUBDIR_CCFLAGS) $(subdir-ccflags-y) # Figure out what we need to build from the various variables # =========================================================================== -# Linker tables objects always wish to be built to avoid bit-rot in -# code, but only linked in *iff* they were enabled. We accomplish this -# using pegging linker table objects into extra-y, which forces -# compilation and then using the respective table-y and table-m as -# as hints for things we do want enabled. Objects which we want to -# avoid linking in will be in table-, not table-y and table-m. -extra-y += $(table-) -obj-m += $(table-m) -obj-y += $(table-y) +ifeq ($(CONFIG_BUILD_AVOID_BITROT),y) +extra-y += $(table-obj-) $(table-lib-) +endif + +obj-m += $(table-obj-m) +obj-y += $(table-obj-y) +lib-m += $(table-lib-m) +lib-y += $(table-lib-y) # When an object is listed to be built compiled-in and modular, # only build the compiled-in version @@ -82,8 +81,8 @@ real-objs-m := $(foreach m, $(obj-m), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y) # Add subdir path extra-y := $(addprefix $(obj)/,$(extra-y)) -table-y := $(addprefix $(obj)/,$(table-y)) -table-m := $(addprefix $(obj)/,$(table-m)) +table-obj-y := $(addprefix $(obj)/,$(table-obj-y)) +table-obj-m := $(addprefix $(obj)/,$(table-obj-m)) always := $(addprefix $(obj)/,$(always)) targets := $(addprefix $(obj)/,$(targets)) modorder := $(addprefix $(obj)/,$(modorder))