KCoreaddons build failiure on ARM

[Michael Pyne]

On Fri, June 19, 2015 20:40:39 Rohan Garg wrote:
> Hi
> I'm trying to compile kcoreaddons on ARM with clang and I'm hitting
> this build failiure :
> 
> 06:22:27 ../../../src/lib/io/kfilesystemtype.cpp:112:10: error: case
> value evaluates to 2240043254, which cannot be narrowed to type
> '__fsword_t' (aka 'int') [-Wc++11-narrowing]
> 06:22:27     case RAMFS_MAGIC:
> 06:22:27          ^
> 06:22:28 ../../../src/lib/io/kfilesystemtype.cpp:89:32: note: expanded
> from macro 'RAMFS_MAGIC'
> 06:22:28 #  define RAMFS_MAGIC          0x858458F6
> 06:22:28                                ^
> 06:22:28 1 error generated.
> 
> Could someone take a look at it?
> 
> The full build log is here [1]

Hi,

It seems that the `int' type for the ABI you're compiling against is not wide 
enough to support the 'magic' value used to determine the fs type of a file 
system.

But this portion of the code comes more or less from Linux directly (e.g. see 
the man page for statfs(2) to see where the magic values were obtained from). 
I'm not sure what exactly is to be done from here since the narrowing error 
occurs in Linux-specific code (being used here in a Linux-specific code path).

We could cast the value in the switch statement to a wider type here, but if 
glibc is using the not-wide-enough int to hold the magic value then the value 
returned for RAMFS will still not fit in struct statfs (and therefore could 
not compare equal to the actual RAMFS magic).

In short the real solution is for struct statfs to define their __fsword_t 
type to be wider in the first place, but we can't control that.

Regards,
 - Michael Pyne