Beware of subtle bugs due to cpp(1) limitations!
Ruslan Ermilov
ru at FreeBSD.org
Sat Dec 3 14:45:49 PST 2005
Hi there,
cpp(1) only supports integer expressions, so the following
#define FOO foo
#if FOO == bar
will always evaluate to true, because "foo" and "bar" will
be treated as zeroes, as explained in cpp.info.
I've only scanned for _MACHINE_ARCH, because that's how I
discovered it, and there's a couple of places where the
code is broken:
sys/dev/isp/isp_freebsd.h:#if _MACHINE_ARCH == sparc64
sys/dev/ispfw/ispfw.c:#if _MACHINE_ARCH == sparc64
sys/dev/ispfw/ispfw.c:#if _MACHINE_ARCH == sparc64
sys/dev/ispfw/ispfw.c:#if _MACHINE_ARCH == sparc64
sys/gnu/fs/reiserfs/reiserfs_fs.h:#if (_MACHINE_ARCH == amd64)
sys/netgraph/ng_vjc.c:#if _MACHINE_ARCH == i386
sys/netgraph/ng_vjc.c:#elif _MACHINE_ARCH == alpha
sys/netgraph/ng_vjc.c:#error Unspported _MACHINE_ARCH
In these cases, the right tests would be #ifdef __sparc64__.
Other instances (of not _MACHINE_ARCH) may be harder to
fix. The ng_vjc.c is a nice example that clearly
demonstrates (without compiling the code) that it's
broken -- it's compiled on all architectures, but has
the following code:
#if _MACHINE_ARCH == i386
#define NG_VJC_TSTATE_PTR_TYPE &ng_parse_uint32_type
#elif _MACHINE_ARCH == alpha
#define NG_VJC_TSTATE_PTR_TYPE &ng_parse_uint64_type
#else
#error Unspported _MACHINE_ARCH
#endif
The season for more bugs of this type is declared open! :-)
Cheers,
--
Ruslan Ermilov
ru at FreeBSD.org
FreeBSD committer
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