Clang buildworld failure due to multiple definitions of __isnanf
eric at shadowsun.net
Mon Jun 27 02:32:05 UTC 2011
I've both seen reports and experienced make buildworld with clang
failing in usr.bin/xlint/lint1 (really, make kernel-toolchain is what
fails), because lint1 is statically linked, and there is a definition of
__isnanf in both libc and libm. GCC, on the other hand, builds just fine.
The file tree.c in usr.bin/xlint/lint1 calls both isnan and finite from
math.h. After some investigation, I figured out what's going on.
math.h includes a macro version of isnan, which expands out to an
expression that calls isnan, __isnanl, and __isnanf. GCC seems to treat
all of these as builtin functions, and implements them with its code
generator, rather than generating calls. Clang, on the other hand, does
not, which leaves calls to __isnanf in the resulting object file, which
will result in multiple definitions at link time.
There are several possible solutions. The workaround I used is to add
-Wl,--allow-multiple-definition to LDADD in the makefile for xlint.
A better solution, I think, is to modify math.h with something like this:
#define isnan(n) __builtin_isnan(n)
(It might be a good idea to add these kinds of definitions for all of
clang's builtins, actually.)
Anyway, I hope this helps someone.
PS. Sorry I don't have build logs, assembler output, etc. My FreeBSD
machine's wireless card isn't supported (yet).
Computer Science Ph.D Student,
University of Massachusetts
Research Intern, IBM Research
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