Messages in this thread | | | Date | Thu, 28 Aug 2008 00:40:32 -0700 (PDT) | Subject | Re: linux-next: build failure | From | David Miller <> |
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From: Stephen Rothwell <sfr@canb.auug.org.au> Date: Mon, 25 Aug 2008 21:28:33 +1000
> Hi Ingo, > > Today's linux-next build (sparc64 defconfig) failed like this: > > ERROR: "__BUILD_BUG_ON_non_constant" [drivers/net/sunvnet.ko] undefined! > ERROR: "__BUILD_BUG_ON_non_constant" [drivers/block/sunvdc.ko] undefined! > > Probably intorduced by commit f5b5d41dd51a31fe70e3a04fb80a3b90b84c6a4e > ("debug: fix BUILD_BUG_ON() for non-constant expressions").
I think __builtin_constant_p() is not seeing something it should here.
It isn't accepting:
-------------------- static inline __attribute__((const)) bool is_power_of_2(unsigned long n) { return (n != 0 && ((n & (n - 1)) == 0)); } --------------------
and thus is_power_of_2(256) as being a constant.
If a 'const' inline function being passed a const argument isn't constant, what is! :-)
I bet the problem is the fact that is_power_of_2() is a function.
I did some tests and I can only trigger this problem with gcc-3.4 on sparc, gcc-4.1 and gcc-4.2 worked fine.
It triggers with both -O2 and -Os for the following simple test case:
static inline __attribute__((const)) int is_power_of_2(unsigned long n) { return (n != 0 && ((n & (n - 1)) == 0)); }
extern int bar;
int main(void) { if (!__builtin_constant_p(is_power_of_2(256))) bar++; return 0; }
davem@sunset:~/src/GIT/linux-2.6$ gcc-3.4 -Os -o x x.c /tmp/ccy8FzD8.o: In function `main': x.c:(.text+0x0): undefined reference to `bar' x.c:(.text+0x4): undefined reference to `bar' x.c:(.text+0xc): undefined reference to `bar' collect2: ld returned 1 exit status davem@sunset:~/src/GIT/linux-2.6$ gcc-3.4 -O2 -o x x.c /tmp/ccQNzZuj.o: In function `main': x.c:(.text+0x0): undefined reference to `bar' x.c:(.text+0x4): undefined reference to `bar' x.c:(.text+0xc): undefined reference to `bar' collect2: ld returned 1 exit status davem@sunset:~/src/GIT/linux-2.6$
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