[PATCH] usage: fix a sparse 'redeclared with different type' error

[PATCH] usage: fix a sparse 'redeclared with different type' error

[Ramsay Jones]

Signed-off-by: Ramsay Jones <ramsay@ramsayjones.plus.com>
---

Hi Jeff,

If you need to re-roll your 'jk/bug-to-abort' branch, could you please
squash this into the relevant patch (commit d8193743e0 "usage.c: add
BUG() function", 12-05-2017).

[Just FYI, sparse complains thus:
  usage.c:212:6: error: symbol 'BUG_fl' redeclared with different type
  (originally declared at git-compat-util.h:1076) - different modifiers
]

Thanks!

ATB,
Ramsay Jones

 usage.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/usage.c b/usage.c
index 545136734..918b539bc 100644
--- a/usage.c
+++ b/usage.c
@@ -209,6 +209,7 @@ static NORETURN void BUG_vfl(const char *file, int line, const char *fmt, va_lis
 }
 
 #ifdef HAVE_VARIADIC_MACROS
+__attribute__((format (printf, 3, 4))) NORETURN
 void BUG_fl(const char *file, int line, const char *fmt, ...)
 {
 	va_list ap;
@@ -217,6 +218,7 @@ void BUG_fl(const char *file, int line, const char *fmt, ...)
 	va_end(ap);
 }
 #else
+__attribute__((format (printf, 1, 2))) NORETURN
 void BUG(const char *fmt, ...)
 {
 	va_list ap;
-- 
2.13.0

Re: [PATCH] usage: fix a sparse 'redeclared with different type' error

[Jeff King]

On Tue, May 16, 2017 at 02:11:40AM +0100, Ramsay Jones wrote:

> 
> If you need to re-roll your 'jk/bug-to-abort' branch, could you please
> squash this into the relevant patch (commit d8193743e0 "usage.c: add
> BUG() function", 12-05-2017).
> 
> [Just FYI, sparse complains thus:
>   usage.c:212:6: error: symbol 'BUG_fl' redeclared with different type
>   (originally declared at git-compat-util.h:1076) - different modifiers
> ]

Hmm. Our model here is the die() function, which gets noreturn and
format attributes in the declaration, but only noreturn at the
definition.

Your patch here adds both attributes to the definition:

> +__attribute__((format (printf, 3, 4))) NORETURN
>  void BUG_fl(const char *file, int line, const char *fmt, ...)

Another possible model is trace_printf_key_fl(), which just has a format
attribute at the declaration, and nothing at all in the definition.

So it seems like this doesn't matter for the format attribute, but does
for NORETURN. Weird. I wonder if it's specific to the attribute, or
something about the way we hide it behind a macro.

There probably isn't a downside to repeating the format attribute, I
guess. Except that I'm not sure what happens if the two ever got out of
sync (gcc doesn't seem to complain, though in practice you'd probably
change the order or number of arguments at the same time, which is
likely to cause a mismatch).

-Peff

Re: [PATCH] usage: fix a sparse 'redeclared with different type' error

[Ramsay Jones]

On 16/05/17 04:02, Jeff King wrote:
> On Tue, May 16, 2017 at 02:11:40AM +0100, Ramsay Jones wrote:
> 
>>
>> If you need to re-roll your 'jk/bug-to-abort' branch, could you please
>> squash this into the relevant patch (commit d8193743e0 "usage.c: add
>> BUG() function", 12-05-2017).
>>
>> [Just FYI, sparse complains thus:
>>   usage.c:212:6: error: symbol 'BUG_fl' redeclared with different type
>>   (originally declared at git-compat-util.h:1076) - different modifiers
>> ]
> 
> Hmm. Our model here is the die() function, which gets noreturn and
> format attributes in the declaration, but only noreturn at the
> definition.

Yes, in this case, it's only noreturn that matters (sparse only
cares about a subset of attributes).

> Your patch here adds both attributes to the definition:
> 
>> +__attribute__((format (printf, 3, 4))) NORETURN
>>  void BUG_fl(const char *file, int line, const char *fmt, ...)

Yes, my initial patch only added the NORETURN, but I decided it
didn't hurt to make the header and c-file 'match' in this case. ;-)

> There probably isn't a downside to repeating the format attribute, I
> guess. Except that I'm not sure what happens if the two ever got out of
> sync (gcc doesn't seem to complain, though in practice you'd probably
> change the order or number of arguments at the same time, which is
> likely to cause a mismatch).

If you prefer, you can simply add the NORETURN, since that eliminates
the error message just as well.

ATB,
Ramsay Jones

Re: [PATCH] usage: fix a sparse 'redeclared with different type' error

[Luc Van Oostenryck]

On Tue, May 16, 2017 at 5:02 AM, Jeff King <peff@peff.net> wrote:
> On Tue, May 16, 2017 at 02:11:40AM +0100, Ramsay Jones wrote:
>
>>
>> If you need to re-roll your 'jk/bug-to-abort' branch, could you please
>> squash this into the relevant patch (commit d8193743e0 "usage.c: add
>> BUG() function", 12-05-2017).
>>
>> [Just FYI, sparse complains thus:
>>   usage.c:212:6: error: symbol 'BUG_fl' redeclared with different type
>>   (originally declared at git-compat-util.h:1076) - different modifiers
>> ]
>
> Hmm. Our model here is the die() function, which gets noreturn and
> format attributes in the declaration, but only noreturn at the
> definition.

It's because a deficiency of sparse: the format attribute is simply ignored
while the NORETURN is treated as a 'modifiers' not much different than
'const' or 'extern'.
But the real problem here with sparse is that while it indeed compare
the declaration with the definition, this is done not by checking compatibility
but by strict equality. In other words, the NORETURN, but also a 'static',
in the declaration should be somehow inherited in a subsequent definition
but sparse doesn't do that yet.

-- Luc Van Oostenryck