Re: [PATCH] Enable '-Werror' by default for all kernel builds

[Linus Torvalds]

[ Adding some subsystem maintainers ]

On Mon, Sep 6, 2021 at 10:06 AM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
>
> > But hopefully most cases are just "people haven't cared enough" and
> > easily fixed.
>
> We'll see. For my testbed I disabled the new configuration flag
> for the time being because its primary focus is boot tests, and
> there won't be any boot tests if images fail to build.

Sure, reasonable.

I've checked a few of the build errors by doing the appropriate cross
compiles, and it doesn't seem bad - but it does seem like we have a
number of really pointless long-standing warnings that should have
been fixed long ago.

For example, looking at sparc64, there are several build errors due to
those warnings now being fatal:

 - drivers/gpu/drm/ttm/ttm_pool.c:386

   This is a type mismatch error. It looks like __fls() on sparc64
returns 'int'. And the ttm_pool.c code assumes it returns 'unsigned
long'.

   Oddly enough, the very line after that line does "min_t(unsigned
int" to get the types in line.

   So  the immediate reason is "sparc64 is different". But the deeper
reason seems to be that ttm_pool.c has odd type assumptions. But that
warning should have been fixed long ago, either way.

   Christian/Huang? I get the feeling that both lines in that file
should use the min_t(). Hmm?

 - drivers/input/joystick/analog.c:160

   #warning Precise timer not defined for this architecture.

   Unfortunate. I suspect that warning just has to be removed. It has
never caused anything to be fixed, it's old to the point of predating
the git history. Dmitry?

 - at least a couple of stringop-overread errors. Attached is a
possible for for one of them.

The stringop overread is odd, because another one of them is

   fs/qnx4/dir.c: In function ‘qnx4_readdir’:
   fs/qnx4/dir.c:51:32: error: ‘strnlen’ specified bound 48 exceeds
source size 16 [-Werror=stringop-overread]
      51 |                         size = strnlen(de->di_fname, size);
         |                                ^~~~~~~~~~~~~~~~~~~~~~~~~~~

but I'm not seeing why that one happens on sparc64, but not on arm64
or x86-64. There doesn't seem to be anything architecture-specific
anywhere in that area.

Funky.

Davem - attached patch compiles cleanly for me, but I'm not sure it's
necessarily the right thing to do, and I didn't check the code
generation. Maybe it screws up. Can somebody test on sparc64 and
perhaps think about it more than I did?

               Linus
 arch/sparc/kernel/mdesc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/sparc/kernel/mdesc.c b/arch/sparc/kernel/mdesc.c
index 8e645ddac58e..30f171b7b00c 100644
--- a/arch/sparc/kernel/mdesc.c
+++ b/arch/sparc/kernel/mdesc.c
@@ -39,6 +39,7 @@ struct mdesc_hdr {
 	u32	node_sz; /* node block size */
 	u32	name_sz; /* name block size */
 	u32	data_sz; /* data block size */
+	char	data[];
 } __attribute__((aligned(16)));
 
 struct mdesc_elem {
@@ -612,7 +613,7 @@ EXPORT_SYMBOL(mdesc_get_node_info);
 
 static struct mdesc_elem *node_block(struct mdesc_hdr *mdesc)
 {
-	return (struct mdesc_elem *) (mdesc + 1);
+	return (struct mdesc_elem *) mdesc->data;
 }
 
 static void *name_block(struct mdesc_hdr *mdesc)