Re: [PATCH] libtracefs: improve reproducibility

On Mon, 24 Mar 2025 16:59:11 -0700
Oleh Matiusha <[email protected]> wrote:

> Currently, the files generated by flex & bison are present among sources
> to ease builds for people lacking these tools. However, make rules for them
> are also present in Makefile, and while fetching source code, targets might
> or might not be created with timestamps older than their prerequisites.
> This means in build environments with flex and/or bison available, the
> decision whether headers will be regenerated from sqlhist.l and sqlhist.y
> is random. Since more fresh versions of these tools make different outputs,
> this breaks build determinism, which is essential for people wanting their
> builds to be reproducible. Assuming those who have their own flex & bison
> want headers to be generated by fresh versions, I modified Makefile to check
> for them and add corresponding targets to .PHONY to force re-generation,
> retaining fallback option in case of their absence.
> 

Thanks, it is annoying even if it tries to build them because of the way
git handles timestamps.

I think I rather just have the make targets for them be generated by a new
main target.

Something like this:

diff --git a/Makefile b/Makefile
index bd5c76bcd4f0..6e8022609ee7 100644
--- a/Makefile
+++ b/Makefile
@@ -400,6 +400,9 @@ sqlhist: samples/sqlhist
 samples: libtracefs.a force
 	$(Q)$(call descend,$(src)/samples,all)
 
+sqlhist_remake:
+	$(Q)$(call descend,$(src)/src,sqlhist_remake)
+
 clean: clean_meson
 	$(Q)$(call descend_clean,utest)
 	$(Q)$(call descend_clean,src)
diff --git a/src/Makefile b/src/Makefile
index be81059ce10a..d981d802f8b1 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -46,18 +46,20 @@ $(LIBTRACEFS_SHARED_SO): $(LIBTRACEFS_SHARED_VERSION)
 libtracefs.so: $(LIBTRACEFS_SHARED_SO)
 
 # bison will create both sqlhist.tab.c and sqlhist.tab.h
-sqlhist.tab.h:
-sqlhist.tab.c: sqlhist.y sqlhist.tab.h
-	bison --debug -v --report-file=bison.report -d -o $@ $<
+sqlhist.tab_gen.h:
+sqlhist.tab_gen.c: sqlhist.y sqlhist.tab.h
+	bison --debug -v --report-file=bison.report -d -o $(subst _gen,,$@) $<
 
-sqlhist-lex.c: sqlhist.l sqlhist.tab.c
-	flex -o $@ $<
+sqlhist-lex_gen.c: sqlhist.l sqlhist.tab.c
+	flex -o $(subst _gen,,$@) $<
 
 $(bdir)/%.o: %.c
 	$(Q)$(call do_fpic_compile)
 
 tracefs-sqlhist.o: sqlhist.tab.h
 
+sqlhist_remake: sqlhist.tab_gen.c sqlhist-lex_gen.c
+
 $(OBJS): | $(bdir)
 
 clean:
@@ -67,4 +69,4 @@ clean:
 
 $(bdir)/tracefs-sqlhist.o tracefs-sqlhist.o: sqlhist.tab.h
 
-.PHONY: $(LIBTRACEFS_SHARED_SO) $(LIBTRACEFS_STATIC)
+.PHONY: $(LIBTRACEFS_SHARED_SO) $(LIBTRACEFS_STATIC) sqlhist.tab_gen.c sqlhist-lex_gen.c


Then we don't need to worry about these being built when they are not
needed to be built. If the source files change, then you need to do:

  make sqlhist_remake

to build it again.

Thoughts,

-- Steve