Re: [PATCH] config.mak.dev: add -Wformat

[Junio C Hamano <gitster@pobox.com>]

Jonathan Nieder <jrnieder@gmail.com> writes:

> In October, Thomas Gummerer wrote:
>> On 10/12, Jonathan Nieder wrote:
>>> Jeff King wrote:
>>> ...
>>>> -Wformat is part of -Wall, which we already turn on by default (even for
>>>> non-developer builds).
> ...
> As discussed in [1], autoconf appears to not put -Wall in CFLAGS:
>
>  $ make configure
>      GEN configure
>  $ ./configure
> [...]
>  config.status: creating config.mak.autogen
>  config.status: executing config.mak.autogen commands
>  $ grep CFLAGS config.mak.autogen
>  CFLAGS = -g -O2
>  PTHREAD_CFLAGS=-pthread
>
> So this trap for the unwary is still around.
>
> Can we revive this patch?  Does it just need a clearer commit message,
> or were there other objections?

I think it is a good idea to give fallback/redundancy for this
case.  I do not have strong opinion between -Wall and -Wformat,
but I'd probably vote for the former if pressed.

-- >8 --
From: Thomas Gummerer <t.gummerer@gmail.com>
Date: Fri, 12 Oct 2018 19:40:37 +0100
Subject: [PATCH] config.mak.dev: add -Wformat

801fa63a90 ("config.mak.dev: add -Wformat-security", 2018-09-08)
added the "-Wformat-security" to the flags set in config.mak.dev.
In the gcc man page this is documented as:

         If -Wformat is specified, also warn about uses of format
         functions that represent possible security problems.  [...]

The commit did however not add the "-Wformat" flag, but instead
relied on the fact that "-Wall" is set in the Makefile by default
and that "-Wformat" is part of "-Wall".

Unfortunately, those who use config.mak.autogen generated with the
autoconf to configure toolchain do *not* get "-Wall" in their CFLAGS
and the added -Wformat-security had no effect.  Worse yet, newer
versions of gcc (gcc 8.2.1 in this particular case) warn about the
lack of "-Wformat" and thus compilation fails only with this option
set.

We could fix it by adding "-Wformat", but in general we do want all
checks included in "-Wall", so let's add it to config.mak.dev to
cover more cases.

Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Helped-by: Jeff King <peff@peff.net>
Helped-by: Jonathan Nieder <jrnieder@gmail.com>
[jc: s/-Wformat/-Wall/]
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 config.mak.dev | 1 +
 1 file changed, 1 insertion(+)

diff --git a/config.mak.dev b/config.mak.dev
index bfbd3df4e8..74337f1f92 100644
--- a/config.mak.dev
+++ b/config.mak.dev
@@ -1,6 +1,7 @@
 ifeq ($(filter no-error,$(DEVOPTS)),)
 CFLAGS += -Werror
 endif
+CFLAGS += -Wall
 CFLAGS += -Wdeclaration-after-statement
 CFLAGS += -Wformat-security
 CFLAGS += -Wno-format-zero-length
-- 
2.20.1-2-gb21ebb671b