On 31.03.2020 12:30, Anthony PERARD wrote: > The if_changed macro from Linux, in addition to check if any files > needs an update, check if the command line has changed since the last > invocation. The latter will force a rebuild if any options to the > executable have changed. > > if_changed_rule checks dependencies like if_changed, but execute > rule_$(1) instead of cmd_$(1) when a target needs to be rebuilt. A rule_ > macro can call more than one cmd_ macro. One of the cmd_ macro in a > rule need to be call using a macro that record the command line, so > cmd_and_record is introduced. It is similar to cmd_and_fixup from > Linux but without a call to fixdep which we don't have yet. (We will > later replace cmd_and_record by cmd_and_fixup.) > > Example of a rule_ macro: > define rule_cc_o_c > $(call cmd_and_record,cc_o_o) > $(call cmd,objcopy) > endef > > This needs one of the call to use cmd_and_record, otherwise no .*.cmd > file will be created, and the target will keep been rebuilt. > > In order for if_changed to works correctly, we need to load the .%.cmd > files that the macro generates, this is done by adding targets in to > the $(targets) variable. We use intermediate_targets to add %.init.o > dependency %.o to target since there aren't in obj-y. > > We also add $(MAKECMDGOALS) to targets so that when running for > example `make common/memory.i`, make will load the associated .%.cmd > dependency file. > > Beside the if_changed*, we import the machinery used for a "beautify > output". The important one is when running make with V=2 which help to > debug the makefiles by printing why a target is been rebuilt, via the > $(echo-why) macro. > > if_changed and if_changed_rule aren't used yet. > > Most of this code is copied from Linux v5.4, including the > documentation. > > Signed-off-by: Anthony PERARD <anthony.per...@citrix.com>
Acked-by: Jan Beulich <jbeul...@suse.com> with ... > --- a/docs/misc/xen-makefiles/makefiles.rst > +++ b/docs/misc/xen-makefiles/makefiles.rst > @@ -85,3 +85,102 @@ Compilation flags > > CFLAGS-y specifies options for compiling with $(CC). > AFLAGS-y specifies assembler options. > + > + > +Build system infrastructure > +=========================== > + > +This chapter describe some of the macro used when building Xen. > + > +Macros > +------ > + > + > + if_changed > + if_changed is the infrastructure used for the following commands. > + > + Usage:: > + > + target: source(s) FORCE > + $(call if_changed,ld/objcopy/...) > + > + When the rule is evaluated, it is checked to see if any files > + need an update, or the command line has changed since the last > + invocation. The latter will force a rebuild if any options > + to the executable have changed. > + Any target that utilises if_changed must be listed in $(targets), > + otherwise the command line check will fail, and the target will > + always be built. > + if_changed may be used in conjunction with custom commands as > + defined in "Custom commands". > + > + Note: It is a typical mistake to forget the FORCE prerequisite. > + Another common pitfall is that whitespace is sometimes > + significant; for instance, the below will fail (note the extra space > + after the comma):: > + > + target: source(s) FORCE > + > + **WRONG!** $(call if_changed, ld/objcopy/...) > + > + Note: > + if_changed should not be used more than once per target. > + It stores the executed command in a corresponding .cmd ... the odd mixing of tabs and spaces here taken care of (I didn't check if there are more) and ... > + > + file and multiple calls would result in overwrites and ... the apparently stray blank like here dropped. Jan
