Re: [PATCH 5/5] s390x/tcg: fix format-truncation warning

[Thomas Huth]

On 28/03/2022 12.22, Marc-André Lureau wrote:
> Hi
>
> On Mon, Mar 28, 2022 at 12:59 PM Thomas Huth <thuth@redhat.com> wrote:
> > On 28/03/2022 10.47, marcandre.lureau@redhat.com wrote:
> > > From: Marc-André Lureau <marcandre.lureau@redhat.com>
> > >
> > > ../target/s390x/tcg/translate.c: In function ‘s390x_translate_init’:
> > > ../target/s390x/tcg/translate.c:224:64: error: ‘%d’ directive output may be 
> > > truncated writing between 1 and 11 bytes into a region of size 3 
> > > [-Werror=format-truncation=]
> > >     224 |         snprintf(cpu_reg_names[i], sizeof(cpu_reg_names[0]), "r%d", 
> > > i);
> > >         |                                                                ^~
> > >
> > > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > > ---
> > >    target/s390x/tcg/translate.c | 4 ++--
> > >    1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/target/s390x/tcg/translate.c b/target/s390x/tcg/translate.c
> > > index 5acfc0ff9b4e..a082342a0424 100644
> > > --- a/target/s390x/tcg/translate.c
> > > +++ b/target/s390x/tcg/translate.c
> > > @@ -199,7 +199,7 @@ static TCGv_i64 regs[16];
> > >
> > >    void s390x_translate_init(void)
> > >    {
> > > -    int i;
> > > +    size_t i;
> > >
> > >        psw_addr = tcg_global_mem_new_i64(cpu_env,
> > >                                          offsetof(CPUS390XState, psw.addr),
> > > @@ -221,7 +221,7 @@ void s390x_translate_init(void)
> > >                                       "cc_vr");
> > >
> > >        for (i = 0; i < 16; i++) {
> > > -        snprintf(cpu_reg_names[i], sizeof(cpu_reg_names[0]), "r%d", i);
> > > +        snprintf(cpu_reg_names[i], sizeof(cpu_reg_names[0]), "r%zu", i);
> >
> > The compiler is *really* too stupid to see that i is in the range between 0
> > and 16 here??? ... that rather sounds like a compiler bug to me than
> > something that we should work-around in the QEMU source code. Considering
> > that you're using a x.0 release of GCC, please file a bug against GCC
> > instead. If they refuse to fix it for GCC 12.1 or later, we can revisit this
> > patch, but currently, I really think this should be fixed in GCC instead.
>
> I opened: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105080
>
> Although I think the "workaround" is simple and would avoid users &
> distributions having to add --disable-werror, and possibly miss other
> issues.

But I really dislike adding such noise to the history (it spoils "git blame" 
for example) if it is not really necessary. In this case, it also rather 
helps to show distros that they are shipping a buggy compiler and they 
should fix their compiler instead before it hits their users. So I think it 
would be rather bad to fix this in QEMU now.

 Thomas