asm-generic/int-ll64.h wrongly used on x86_64?

asm-generic/int-ll64.h wrongly used on x86_64?

[Cyril Hrubis]

Hi!
I was writing simple userspace code that prints the values from the
struct statx the line in question looks like:

	printf("%" PRIu64 "\n", st.stx_size);

This unexpectedly gives me warning on x86_64:

warning: format '%lu' expects argument of type 'long unsigned int', but argument 5 has type '__u64' {aka 'long long unsigned int'}

Digging into the issue I've found that include/asm-generic/types.h looks like:

#ifndef _ASM_GENERIC_TYPES_H
#define _ASM_GENERIC_TYPES_H
/*
 * int-ll64 is used everywhere now.
 */
#include <asm-generic/int-ll64.h>

#endif /* _ASM_GENERIC_TYPES_H */

Which is the cause why you cannot print __u64 with PRIu64 and would
force every userspace code to explicitly cast any __u64 in order to get
rid warnings. I would say that it would be better to fix the headers so
that __u64 has the same type as uint64_t so that PRIu64 could be then
used to print __u64 as well.

-- 
Cyril Hrubis
chrubis@suse.cz

Re: asm-generic/int-ll64.h wrongly used on x86_64?

[Florian Weimer]

* Cyril Hrubis:

> Hi!
> I was writing simple userspace code that prints the values from the
> struct statx the line in question looks like:
>
> 	printf("%" PRIu64 "\n", st.stx_size);
>
> This unexpectedly gives me warning on x86_64:
>
> warning: format '%lu' expects argument of type 'long unsigned int', but argument 5 has type '__u64' {aka 'long long unsigned int'}

The correct format depends on whether you use struct statx from the
glibc headers or the Linux UAPI headers.  glibc uses uint64_t, Linux
uses __u64.  uint64_t in glibc prefers unsigned long if the type is
64-bit, Linux uses unsigned long long unconditionally.

One solution is to use %ju and cast to (uintmax_t).  Other cast-based
approaches are possible as well.

I'm not happy with the situation because those casts reduce type safety
and may suppress relevant compiler warnings.

Thanks,
Florian

Re: asm-generic/int-ll64.h wrongly used on x86_64?

[Cyril Hrubis]

Hi!
> The correct format depends on whether you use struct statx from the
> glibc headers or the Linux UAPI headers.  glibc uses uint64_t, Linux
> uses __u64.  uint64_t in glibc prefers unsigned long if the type is
> 64-bit, Linux uses unsigned long long unconditionally.
> 
> One solution is to use %ju and cast to (uintmax_t).  Other cast-based
> approaches are possible as well.
> 
> I'm not happy with the situation because those casts reduce type safety
> and may suppress relevant compiler warnings.

I still do not get why can't the kernel __u64 match the uint64_t at
least in userspace. It should be as easy as:

diff --git a/include/uapi/asm-generic/types.h b/include/uapi/asm-generic/types.h
index dfaa50d99d8f..3c9a1fc5d5c3 100644
--- a/include/uapi/asm-generic/types.h
+++ b/include/uapi/asm-generic/types.h
@@ -2,8 +2,12 @@
 #ifndef _ASM_GENERIC_TYPES_H
 #define _ASM_GENERIC_TYPES_H
 /*
- * int-ll64 is used everywhere now.
+ * int-ll64 is used everywhere in kernel now.
  */
-#include <asm-generic/int-ll64.h>
+#if __BITS_PER_LONG == 64 && !__KERNEL__
+# include <asm-generic/int-l64.h>
+#else
+# include <asm-generic/int-ll64.h>
+#if

 #endif /* _ASM_GENERIC_TYPES_H */


-- 
Cyril Hrubis
chrubis@suse.cz