Kang-Che Sung wrote:
2017年10月8日 18:50，"James Clarke" <jrt...@jrtc27.com
<mailto:jrt...@jrtc27.com>>寫道：
On 8 Oct 2017, at 02:34, Kang-Che Sung <explore...@gmail.com
<mailto:explore...@gmail.com>> wrote:
> On Sun, Oct 8, 2017 at 1:53 AM, James Clarke <jrt...@jrtc27.com
<mailto:jrt...@jrtc27.com>> wrote:
>> diff --git a/libbb/xfuncs.c b/libbb/xfuncs.c
>> index 9cbfb2836..95dac656a 100644
>> --- a/libbb/xfuncs.c
>> +++ b/libbb/xfuncs.c
>> @@ -22,6 +22,16 @@
>> */
>> #include "libbb.h"
>>
>> +#ifndef IMAXBEL
>> +# define IMAXBEL 0
>> +#endif
>> +#ifndef IUCLC
>> +# define IUCLC 0
>> +#endif
>> +#ifndef IXANY
>> +# define IXANY 0
>> +#endif
>> +
>
> I wonder, how do these break, and why does defining them as 0
solve the problem?
FreeBSD (well, GNU/kFreeBSD at least) does not define IUCLC. They
are only used
in the line:
> newterm.c_iflag &=
~(BRKINT|INLCR|ICRNL|IXON|IXOFF|IUCLC|IXANY|IMAXBEL);
Thus, by defining them as 0 when not present, it is as if they
were omitted
from that list, without needing a bunch of confusing #ifdef's in
the expression
itself. While IMAXBEL and IXANY are defined everywhere Debian
cares about, they
are still non-standard, so I did the same for them in case there
is a platform
out there without them.
Why not just fix that usage line so that the bitwise OR's are all
enclosed in #ifdef lines? I think it's better than defining the macros
to a value that may cause further problems when reused.
Because the way the line is now is one line with 8 values. Changing that
to use ifdefs for each value would change that one line to 3*8+2=26
lines, that makes the code much harder to read and maintain. And there
may be other places where it is used. It's perfectly legitimate to
define the values as 0, like you would define O_BINARY as 0 on platforms
that don't need/supply it.
Analogy: You probably won't define an unsupported signal, say SIGUSR3,
to a zero value anyway. They are undefined for a reason. Hope you
understand.
There is nothing wrong with that. It is possible to use "#if SIGUSR3" to
test for SIGUSR being defined and nonzero. It has the additional benefit
that you can use the value in a C statement (as opposed to a C
preprocessor test) and let the compiler optimize it out. Busybox does
that a lot.
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