Re: [PATCH, PR67627][RFC] broken libatomic multilib parallel build

[Szabolcs Nagy <szabolcs dot nagy at arm dot com>]

On 04/12/15 12:39, Szabolcs Nagy wrote:
> As described in pr other/67627, the all-multi target can be
> built in parallel with the %_.lo targets which generate make
> dependencies that are parsed during the build of all-multi.
>
> gcc -MD does not generate the makefile dependencies in an
> atomic way so make can fail if it concurrently parses those
> half-written files.
> (not observed on x86, but happens on arm native builds.)
>
> this workaround forces all-multi to only run after the *_.lo
> targets are done, but there might be a better solution using
> automake properly. (automake should know about the generated
> make dependency files that are included into the makefile so
> no manual tinkering is needed to get the right build order,
> but i don't know how to do that.)
>
> 2015-12-04  Szabolcs Nagy <szabolcs.nagy@arm.com>
>
>      PR other/67627
>      * Makefile.am (all-multi): Add dependency.
>      * Makefile.in: Regenerate.

ping
and cc rth (as his name is on this makefile).

> diff --git a/libatomic/Makefile.am b/libatomic/Makefile.am
> index bd0ab29..38c635f 100644
> --- a/libatomic/Makefile.am
> +++ b/libatomic/Makefile.am
> @@ -139,3 +139,10 @@ endif
>
>   libatomic_convenience_la_SOURCES = $(libatomic_la_SOURCES)
>   libatomic_convenience_la_LIBADD = $(libatomic_la_LIBADD)
> +
> +# Override the automake generated all-multi rule to guarantee that all-multi
> +# is not run in parallel with the %_.lo rules which generate $(DEPDIR)/*.Ppo
> +# makefile fragments to avoid broken *.Ppo getting included into the Makefile
> +# when it is reloaded during the build of all-multi.
> +all-multi: $(libatomic_la_LIBADD)
> +	$(MULTIDO) $(AM_MAKEFLAGS) DO=all multi-do # $(MAKE)
> diff --git a/libatomic/Makefile.in b/libatomic/Makefile.in
> index b696d55..a083d87 100644
> --- a/libatomic/Makefile.in
> +++ b/libatomic/Makefile.in
> @@ -496,12 +496,6 @@ clean-libtool:
>
>   distclean-libtool:
>   	-rm -f libtool config.lt
> -
> -# GNU Make needs to see an explicit $(MAKE) variable in the command it
> -# runs to enable its job server during parallel builds.  Hence the
> -# comments below.
> -all-multi:
> -	$(MULTIDO) $(AM_MAKEFLAGS) DO=all multi-do # $(MAKE)
>   install-multi:
>   	$(MULTIDO) $(AM_MAKEFLAGS) DO=install multi-do # $(MAKE)
>
> @@ -800,6 +794,13 @@ vpath % $(strip $(search_path))
>   %_.lo: Makefile
>   	$(LTCOMPILE) $(M_DEPS) $(M_SIZE) $(M_IFUNC) -c -o $@ $(M_SRC)
>
> +# Override the automake generated all-multi rule to guarantee that all-multi
> +# is not run in parallel with the %_.lo rules which generate $(DEPDIR)/*.Ppo
> +# makefile fragments to avoid broken *.Ppo getting included into the Makefile
> +# when it is reloaded during the build of all-multi.
> +all-multi: $(libatomic_la_LIBADD)
> +	$(MULTIDO) $(AM_MAKEFLAGS) DO=all multi-do # $(MAKE)
> +
>   # Tell versions [3.59,3.63) of GNU make to not export all variables.
>   # Otherwise a system limit (for SysV at least) may be exceeded.
>   .NOEXPORT: