depends bdb -Werror=format-security "format not a string literal and no format arguments" #25211

Running make -C depends on nixos with gcc 10.3.0 results in

libtool: compile:  gcc -c -I. -I../dist/./.. -I/home/russ/work/bitcoin/depends/x86_64-pc-linux-gnu/include -D_GNU_SOURCE -D_REENTRANT -pipe -O2 -Wno-error=implicit-function-declaration ../dist/./../txn/txn.c  -fPIC -DPIC -o txn.o
../dist/./../txn/txn.c: In function ‘__txn_begin’:
../dist/./../txn/txn.c:171:3: error: format not a string literal and no format arguments [-Werror=format-security]
  171 |   __db_errx(env, TxnAlloc);
      |   ^~~~~~~~~
../dist/./../txn/txn.c: In function ‘__txn_compensate_begin’:
../dist/./../txn/txn.c:318:3: error: format not a string literal and no format arguments [-Werror=format-security]
  318 |   __db_errx(env, TxnAlloc);
      |   ^~~~~~~~~
cc1: some warnings being treated as errors
make[1]: *** [Makefile:1980: txn.o] Error 1
make[1]: Leaving directory '/home/russ/work/bitcoin/depends/work/build/x86_64-pc-linux-gnu/bdb/4.8.30-1205703c56a/build_unix'
make: *** [funcs.mk:288: /home/russ/work/bitcoin/depends/work/build/x86_64-pc-linux-gnu/bdb/4.8.30-1205703c56a/build_unix/.stamp_built] Error 2
make: Leaving directory '/home/russ/work/bitcoin/depends'

I could work around it with

diff --git a/depends/packages/bdb.mk b/depends/packages/bdb.mk
index dc536fd3991..b69276cb154 100644
--- a/depends/packages/bdb.mk
+++ b/depends/packages/bdb.mk
@@ -14,7 +14,7 @@ $(package)_config_opts_freebsd=--with-pic
 $(package)_config_opts_netbsd=--with-pic
 $(package)_config_opts_openbsd=--with-pic
 $(package)_config_opts_android=--with-pic
-$(package)_cflags+=-Wno-error=implicit-function-declaration
+$(package)_cflags+=-Wno-error=implicit-function-declaration -Wno-error=format-security
 $(package)_cxxflags+=-std=c++17
 $(package)_cppflags_mingw32=-DUNICODE -D_UNICODE
 endef

But I don't know if this is the right fix or if there possibly is a real bug in the code causing the warning.

What is adding -Werror in the first place?

Edit: Oh, BerkeleyDB's build system does?

FWIW, for zeromq we explicitly disable Werror, maybe it makes sense here too:

depends/packages/zeromq.mk:  $(package)_config_opts += --disable-Werror --disable-drafts --enable-option-checking

I think in general it is good to disable Werror for any kind of external packaging. Internally, since we do care very much about dependencies though, it maybe be good to let some warnings trigger errors, particularly security warnings like this one.

In this case it's probably worth looking into the warning to see if it's real. I believe this warning is about printing a c string with printf(c_str) instead of printf("%s", c_str), which can be a bad thing to do.

I could work around it with

I think in this case your suggested patch is the best fix, assuming there's no other warnings causing Werror to blow up in your nix build. I think it's unlikey that we'd patch bdb at this point.