Subject: Re: [PATCH 2/2] fuzz: link fuzz programs with `make all` on Linux

From: Junio C Hamano <[email-masked]>
Date: Tue, 05 Mar 2024 13:44:33 -0800

Josh Steadmon <[email-masked]> writes:

> Since 5e47215080 (fuzz: add basic fuzz testing target., 2018-10-12), we
> have compiled object files for the fuzz tests as part of the default
> 'make all' target. This helps prevent bit-rot in lesser-used parts of
> the codebase, by making sure that incompatible changes are caught at
> build time.
>
> However, since we never linked the fuzzer executables, this did not
> protect us from link-time errors. As of 8b9a42bf48 (fuzz: fix fuzz test
> build rules, 2024-01-19), it's now possible to link the fuzzer
> executables without using a fuzzing engine and a variety of
> compiler-specific (and compiler-version-specific) flags, at least on
> Linux. So let's add a platform-specific option in config.mak.uname to
> link the executables as part of the default `make all` target.
>
> Suggested-by: Junio C Hamano <[email-masked]>
> Signed-off-by: Josh Steadmon <[email-masked]>
> ---
>  Makefile         | 14 +++++++++++---
>  config.mak.uname |  1 +
>  2 files changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index 4e255c81f2..f74e96d7c2 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -409,6 +409,9 @@ include shared.mak
>  # to the "<name>" of the corresponding `compat/fsmonitor/fsm-settings-<name>.c`
>  # that implements the `fsm_os_settings__*()` routines.
>  #
> +# Define LINK_FUZZ_PROGRAMS if you want `make all` to also build the fuzz test
> +# programs in oss-fuzz/.
> +#
>  # === Optional library: libintl ===
>  #
>  # Define NO_GETTEXT if you don't want Git output to be translated.
> @@ -763,9 +766,6 @@ FUZZ_OBJS += oss-fuzz/fuzz-pack-idx.o
>  .PHONY: fuzz-objs
>  fuzz-objs: $(FUZZ_OBJS)
>  
> -# Always build fuzz objects even if not testing, to prevent bit-rot.
> -all:: $(FUZZ_OBJS)
> -
>  FUZZ_PROGRAMS += $(patsubst %.o,%,$(filter-out %dummy-cmd-main.o,$(FUZZ_OBJS)))
>  
>  # Empty...
> @@ -2368,6 +2368,14 @@ ifndef NO_TCLTK
>  endif
>  	$(QUIET_SUBDIR0)templates $(QUIET_SUBDIR1) SHELL_PATH='$(SHELL_PATH_SQ)' PERL_PATH='$(PERL_PATH_SQ)'
>  
> +# Build fuzz programs if possible, or at least compile the object files; even
> +# without the necessary fuzzing support, this prevents bit-rot.
> +ifdef LINK_FUZZ_PROGRAMS
> +all:: $(FUZZ_PROGRAMS)
> +else
> +all:: $(FUZZ_OBJS)
> +endif

It would have been easier on the eyes if we had the fuzz things
together, perhaps like this simplified version?  We build FUZZ_OBJS
either way, and when the LINK_FUZZ_PROGRAMS is requested, we follow
the fuzz-all recipe, too.

diff --git c/Makefile w/Makefile
index 4e255c81f2..46e457a7a8 100644
--- c/Makefile
+++ w/Makefile
@@ -409,6 +409,9 @@ include shared.mak
 # to the "<name>" of the corresponding `compat/fsmonitor/fsm-settings-<name>.c`
 # that implements the `fsm_os_settings__*()` routines.
 #
+# Define LINK_FUZZ_PROGRAMS if you want `make all` to also build the fuzz test
+# programs in oss-fuzz/.
+#
 # === Optional library: libintl ===
 #
 # Define NO_GETTEXT if you don't want Git output to be translated.
@@ -766,6 +769,12 @@ fuzz-objs: $(FUZZ_OBJS)
 # Always build fuzz objects even if not testing, to prevent bit-rot.
 all:: $(FUZZ_OBJS)
 
+# Build fuzz programs, even without the necessary fuzzing support,
+# this prevents bit-rot.
+ifdef LINK_FUZZ_PROGRAMS
+all:: fuzz-all
+endif
+
 FUZZ_PROGRAMS += $(patsubst %.o,%,$(filter-out %dummy-cmd-main.o,$(FUZZ_OBJS)))
 
 # Empty...